The Feeling of Embodiment: A Case Study in Explaining Consciousness
Author: Carruthers, Glenn
Date: 2019-06-07T07:00:00+00:00
Keywords: Psychology; personality; Philosophy; Movements; Phenomenology; Applied Psychology; Mind & Body; Cognitive Psychology & Cognition; General; Psychedelic Library
Description: This book proposes a novel and rigorous explanation of consciousness. It argues that the study of an aspect of our self-consciousness known as the ‘feeling of embodiment’ teaches us that there are two distinct phenomena to be targeted by an explanation of consciousness. First is an explanation of the phenomenal qualities – 'what it is like' – of the experience; and second is the subject's awareness of those qualities. Glenn Carruthers explores the phenomenal qualities of the feeling of embodiment using the tools of quality spaces, as well as the subject's awareness of those qualities as a func
Publisher: Springer

Glenn Carruthers

The Feeling of EmbodimentA Case Study in Explaining Consciousness

Glenn Carruthers

School of Psychology, Charles Sturt University, Port Macquarie, NSW, Australia

ISBN 978-3-030-14166-0e-ISBN 978-3-030-14167-7
https://doi.org/10.1007/978-3-030-14167-7

Library of Congress Control Number: 2019932114

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For Zac and Lizzy.

For Laura and Sid.

Preface and Acknowledgements

The problem of consciousness has been with me just about as long as I can remember. At some point, my best guess is in 1990, mum asked me if I thought the mind was just the activity of the brain or if it was something more. My answer was wrong. Hopefully I am less wrong now. I shied away from the question for a long time, determined to study cosmology instead. But, I’m glad I returned to questions about the nature of the mind and consciousness as an adult. It is a very special kind of question after all. Perhaps this is because we tend to think of consciousness as a very special kind of thing. When Geordi LaForge asks the EnterpriseD computer to build a Holmes style problem capable of defeating Data, the computer doesn’t simply create a more complex problem, nor does it give Moriarty any spectacular superpowers. Instead it makes a conscious Moriarty. Even if I am not inclined to think of consciousness as a kind of magical necessity for creativity and learning, I do agree that being conscious is a pretty special thing. Not everything is conscious, but for those things that are conscious, especially those things that are able to reflect on or think about their own consciousness, that consciousness at least seems to be a defining feature. If we explain our consciousness, we explain something important about ourselves. We know more about what we are, that’s why the conscious Moriarty was such a significant tool in Data’s arc of discovery in his quest to understand humanity.

In the coming pages I offer an evidence-driven account of consciousness as part of our quest to understand ourselves (and not just because studying it is the foundation of my marriage). This project has been so long coming it will be almost impossible to acknowledge everyone who has contributed in a meaningful way. Work toward this book was undertaken whilst I held either student or ECR positions at the University of Adelaide, Humboldt Universität zu Berlin, and Macquarie University. It was, however, completed on taking a lectureship at Charles Sturt University. My thanks go to those institutions and to the people of Australia and Germany who fund them, for their continued dedication education and research in a time when those who would rather we knew less, not more, have disturbingly loud voices.

Many teachers deserve my thanks. Gerard O’Brien, Jon Opie and Garrett Cullity at the University of Adelaide stand out for their support/teaching and in offering me an academic home. I should also acknowledge Gerard and Jon’s forceful naturalism which protected me from many traps. Max Coltheart at Macquarie University stands out for many reasons, but I’d like particularly to point out his encouragement to ignore bad theory and focus on where progress can be made, and for pushing me to do new experiments. My Ph.D. which saw the early development of many ideas in this book was done at two intuitions, due to the necessities of life, my thanks to Gerard O’Brien, Philip Gerrans, John Sutton and Max Coltheart for supervising that project.

As well as my direct teachers I wish to thank all the researchers cited herein, as well as many others whom I have read, or seen present, or had challenge my ideas. Although I can’t list you all this project would not have been the same without you. To this I would add my current and former students, although I think it a little unfair to name names here, you contributed to the development of my ideas in a way that’s difficult to quantify.

Countless ancestors could also be acknowledged of course. But, I’d would especially point out my Grandparents John and Dorothy Edwards who took a family from the slate mines and quarries of Wales to a new life in Australia, creating in just two generations sufficient middle class privilege for my parents Linda and Robert Carruthers to provide me with the (positive) freedom to enter academia and do this work. I’m old enough to remember when nerds weren’t as cool as they are now (I had friends at school assaulted for carrying Star Wars books), so I would especially thank mum and dad for creating an environment where I could develop my passion for science and discovery, and my uncles John Hayden and John Hadley for helping develop that environment.

I should acknowledge to that I am not always easy to work with, and whilst not all of it is attributable to my mental illnesses, some is. I would not be here to finish this book without the work of medical staff in private practice and hospitals, such as Dr. Hany Samir, in Adelaide, Sydney and Berlin. I’m sorry I don’t know all your names to thank you personally.

Quite a few friends and colleagues have inspired and helped me along the way. I couldn’t possibly list everything everyone has done, but I owe much to old friends such as Michael Moran and Lucas Beer; collaborators like Kristina Musholt, Neha Khetrapal, Nick Badcock, Xiaoqing Gao, Rachel Robbins, Alicia Wilcox and Regine Zopf; and those who were happy to meet once a week to discuss these and other ideas, such as Lincoln Colling, Brendan Ritchie, Vince Polito, Stephen Pritchard, Tibor Molnar, Stephane Savanah and many others. I should emphasise my thanks to Regine Zopf, Xiaoqing Gao, Rachel Robbins and Alicia Wilcox who I worked with to test some of the ideas discussed here. My apologies to anyone who I have neglected to list explicitly here. Laura Ruggles and Sidney Carls Diamante stand out for special thanks, you probably remember your contributions better than I, but I can’t imagine doing this without you.

Some people also went above and beyond in reading drafts of this book, or previous papers. My thanks to Laura Ruggles, Elizabeth Schier, Melanie Rosen, Stephen Gadsby, Robert Carruthers, Carmel Sealy, Linda Carruthers, and Jakob Hohwy for your help and tolerating my spelling difficulties. The same of course goes for the editor and reviewers of this book.

My final and biggest thanks go to Elizabeth (Lizzy) Schier. Over the past 13 years Lizzy has been the most wonderful partner in both life and research. She has been an invaluable teacher, has kept me going in the hardest times, and generally made life worth living. Almost all the ideas in this book owe their seeds to discussions with Lizzy and I hope I have done some justice to all I have learnt from her.

Glenn Carruthers Port Macquarie, Australia December 2018

Contents

1 The Real Problem of Consciousness 1

2 The Feeling of Embodiment: Our Target of Explanation 21

3 Off-Line and On-Line Body Representations 51

4 Explaining the Feeling of Embodiment: The Feeling of Embodiment Occurs When an On-Line Body Representation Is Matched to an Off-Line Prototype 73

5 …And Then What Happens? 107

6 Implications of the Real Problem of Consciousness for the Sense of Embodiment: We Need a Hybrid Account of ‘Consciousness’ 119

7 Completing the Hybrid Account: Awareness Is a Functionally Emergent Kind 149

8 Conclusion 175

Author Index 179

Subject Index 183

List of Figures

Fig. 4.1 The causal chain (inside the cognitive system) leading to the sense of embodiment. Sensory information classed as related to some body or not is unified into an on-line body representation of the perceived body. If that body is represented as the same body represented by the off-line body representation then the sense of embodiment is elicited. Such a match involves the on-line body representation falling close to the off-line prototype (see below). Factors influencing whether or not the on-line representation matches the off-line representation are whether or not any proprioceptive or touch information comes from the body represented on-line, whether the body represented on-line is shaped and arranged as one’s body could be and whether or not the body represented on-line moves as predicted. The RHI occurs when the rubber hand is mistaken for the real hand as represented in the off-line model. This is due to an illusory experience of touch coming from a hand which is shaped and arranged in a way which is plausible for one’s own body as represented off-line, and in some conditions that the model hand moves as predicted. In this diagram particular types of mental representation are named in ellipses and are identified by their content. Arrows represent computations over those representations. Thus, the syntax of this diagram departs significantly from the standard form laid out by Coltheart (2002) (Reproduced with permission from Imprint Academic)78

Fig. 4.2 The separation of the causal chain leading to drift from that leading to the illusion. Drift and the illusion share common causes up to the formation of the on-line body representation, which explains why they commonly co-occur (Reproduced with permission from Imprint Academic)81

Fig. 5.1 The spatial layout of the stimuli. In the centre, we see a fixation cross, left and right are two rectangles. A cue appears at the x and disappears, followed by a target at one of the two circles. The subject’s task is to indicate the colour of the target. Subjects respond faster to cues appearing within the same shape as the cue, even though they are as far from the cue as the target in the other shape (Courtesy of Glenn Carruthers)111

Fig. 7.1 The functional organisation of a chocolate maker, after Coltheart (2002)161

© The Author(s) 2019

Glenn CarruthersThe Feeling of Embodimenthttps://doi.org/10.1007/978-3-030-14167-7_1

1. The Real Problem of Consciousness

Glenn Carruthers[1]

(1) School of Psychology, Charles Sturt University, Port Macquarie, NSW, Australia

Glenn Carruthers Email: gcarruthers@csu.edu.au

1.1 Introduction

This book is about consciousness. That is to say it is about experiences. I am not so much interested here in the difference between being awake and being asleep (although that matters an awful lot) as I am in the nature and explanation of experiences. That is to say, particular experiences, because that will help us with many of the problems we encounter here. I want to explain particular experiences. This book is not about what has been called “embodied cognition”, which is, instead the causal or constitutive role bodies (outside of the nervous system) play in cognition. My interest here is how we experience our bodies, and only how we experience our bodies.

This, I take it, is part of the broader project of understanding what we are and how we fit into the world. It matters at least as much as understanding the origins of the universe, the nature of life and how some people can still hold that we ought to be market anarchists. My approach here is to attempt to explain a particular type of experience, which I call the feeling of embodiment. This is the culmination of a decade or so of work in psychology and philosophy. Much of what you will read here you may also find in my previously published papers. One of things I am doing is taking the opportunity to correct some mistakes I made along the way, so I ask that this, rather than the papers be considered the canonical statement of my current views. You are, of course, free to agree with current me, past me or neither.

The approach I take is a rigorously naturalistic approach. I have been convinced that the best way to do philosophy (and treating theoretical psychology as a part of philosophy in the broadest sense) involves using all the resources available to us to understand ourselves and the rest of the world. I’m not going to try and convince you of that here, any more than I will try and convince you that the mind is a representational/computational device, although I work from that basis too.[1] I don’t think that either of these assumptions is deeply problematic, but you might, so it’s worth being honest about my prior commitments.

In saying I am taking a naturalistic approach I mean two things. First, that experiences are not supernatural[2] phenomena. They are a part of the natural world as much as gold, planets and societies are. Second, that theorising should proceed on the basis of fact. This includes, of course, plenty of room to question the interpretation of facts, the relevance of particular facts, the assumptions which lead to their discovery et cetera. My approach has been to gather as many facts as possible about the feeling of embodiment and, in the spirit of transcendental inference (Flanagan, 1984, pp. 182–183), hypothesise as to what the world is like in order to explain those facts. The hypothesis developed is examined to determine any predictions which follow regarding undiscovered facts and then those predictions are tested. Such is how this book proceeds. But first, what is the problem I am trying to solve: this problem of consciousness?

1.2 The Real Problem of Consciousness

The Real problem of consciousness is the problem of explaining experiences. There are, as we shall see as this book progresses, a great deal of worrisome sub-problems, particularly in regards to measurement and acquiring sufficient evidence that a particular experience is occurring or not. These worries are profound and have deep implications for the nature of consciousness, as we shall see in later discussions of confabulation. That said, I see no reason to assume, as the powerful in philosophy commonly do, that consciousness poses a special “Hard Problem” (Chalmers, 1995) or presents an insurmountable “explanatory gap” (Levine, 1983) making consciousness necessarily mysterious. My reason for this, in rough shot, is that arguments for such special kinds of problems assume that consciousness is somehow a supernatural phenomenon or at least assume that consciousness poses a special kind of problem (Carruthers & Schier, 2017). Seeing no reason to believe in the supernatural and finding unconvincing arguments which assume their conclusion, I see no reason to think that consciousness must be mysterious.

Concerns such as the Hard Problem and the explanatory gap are supposed to leave us worrying about the possibility of a science of consciousness. I take it that this book (along with many others) is an existence proof sufficient to overcome that worry. Nonethe-less I do not think that advocates of such problems are stupid, nor wilfully blind. If underlying these concerns about the possibility of a science of consciousness are worries about how sufficient evidence can be acquired, or the adequacy of particular hypotheses in explaining all the facts about experience, then there is much common ground. As I argue in later chapters such worries have profound implications about the nature of consciousness. But they do not lead to any sort of mysterianism, nor to the conclusion that consciousness is supernatural. Why do people think that they do? What are the traditional worries about consciousness and the possibility of studying it which I am avoiding?

Traditional problems of consciousness go beyond the problem of explaining experience and build in worries about the very possibility of consciousness being a part of the natural world. Advocates of these problems deny, or raise concerns about, or are unconvinced by, naturalism (often called materialism or physicalism) about consciousness. Instead they posit that consciousness is, or could be, or must be, supernatural. The reason for building in these worries is the difficulty of seeing any continuity between typical natural phenomena and consciousness. It seems like consciousness is a very different kind of thing which just cannot be explicable in terms of natural things.

1.2.1 Descartes Then the “Hard Problem”

Descartes is a common place to start when raising such concerns. Not the only place by any means, and certainly one that is problematic in that it reinforces traditional power structures in philosophy. Nonethe-less, as my aim here is to distinguish the Real Problem of consciousness from traditional worries, I have little room to move. It is the community and not I alone that determines what tradition is, and so I will work within the community’s constraints.

Traditional worries about consciousness as a supernatural phenomenon are expressed by Descartes in the Meditations on First Philosophy.[3] Although they are not the central concern of the text, which is a response to a kind of radical skepticism, they are well developed. Descartes’ concerns were expressed more as worries that the mind or self (the “I”), rather than just consciousness, must be different from the natural world. But, as he held that consciousness was not only a part of the mind, but, indeed, essential too it (at least in the meditations), the concerns obviously apply to experiences. As we will see the examples he gives of “thoughts”, which are essential to the mind or self, are all experiences.

As early as the synopsis of the Meditations following Descartes’ letter to the Sorbonne we see that central to Descartes’ arguments is the difference in the way the mind appears to him and how bodies (natural things) appear:

This conclusion [that mind and body are different substances – GC] is confirmed in the same Meditation by the fact that we cannot understand a body except as being divisible, while by contrast we cannot understand a mind except as being indivisible. (Descartes & Cottingham, 1996, p. 9 [13])

This purported difference between mind and body (natural thing) is based on the appearance of mind and body to Descartes. That is, on how such things seemed to him. Specifically, he compares how his mind appears to how a piece of bee’s wax appears. Bee’s wax appears to him to be divisible into smaller sections, whereas the mind appears to him as a unified whole. However, that natural things are divisible, and minds are not is not the only difference which Descartes proposes.

Descartes supposes, by way of radically skeptical thought experiments (the famous “evil demon” for example) that the existence of bodies (natural things) can be sensibly doubted (Descartes & Cottingham, 1996, pp. 15 [22–23], 18 [26–27]). In contrast, the existence of the self (the “I”) or mind cannot be doubted, for the very act of doubting proves that it must exist (Descartes & Cottingham, 1996, pp. 16–17 [24–25]).

Furthermore, bodies are defined by a set of properties. In discussing his “mental conception” of bodies (i.e. natural things), Descartes says:

… by a body I understand whatever has a determinable shape and definable location and can occupy a space in such a way as to exclude any other body; it can be perceived by touch, sight, hearing, taste or smell, and can be moved in various ways, not by itself but by whatever else it comes into contact with. (Descartes & Cottingham, 1996, p. 17 [26])

In contrast, the self (“I”) or mind is essentially a thinking thing (Descartes & Cottingham, 1996, p. 18 [27]). Where thoughts are understood as conscious thoughts, but also include what many today would consider as experiences distinct from thinking:

But what then am I? A thing that thinks. What is that? A thing that doubts, understands, affirms, denies, is willing, is unwilling, and also imagines and has sensory perceptions. (Descartes & Cottingham, 1996, p. 19 [28])

Playing with a piece of wax Descartes concludes that bodies (things) are different to minds. Bodies, like wax, are extended in space and are thus divisible (Descartes & Cottingham, 1996, p. 59 [85–86]) and changeable (Descartes & Cottingham, 1996, pp. 20–21 [30–31]). Later he extends this list of properties such that bodies are understood to have shape, location, motion, temporal extension, quantity, and substance (Descartes & Cottingham, 1996, p. 30 [43]). Based on how the mind appears to him, i.e. on introspection, Descartes concludes that some of these properties are shared by the conscious self, but it is not the case that the conscious self [or mind, or conscious thoughts which are essential to the self (the “I”)] is necessarily spatially extended. Thus, it is not essential that the mind has shape, position, or motion (Descartes & Cottingham, 1996, p. 30 [44]). However, as the mind is a substance, albeit of a very different kind (the famous “substance dualism” Descartes & Cottingham, 1996, p. 30 [44]), it is possible that the mind may have such properties contingently, at least whilst it is connected with a body (Descartes & Cottingham, 1996, p. 31 [45]). To Descartes then natural things (bodies) are essentially spatially extended (and thus divisible, located, shaped, and so on) and dubitable whereas minds are essentially thinking, not spatially extended, and indubitable (to the one having the thought).

It is in the 6th Meditation that Descartes nails down the idea that the ‘I’, who is essentially a consciously thinking thing, is a different sort of thing to corporeal bodies and that the justification for this is that the two types of thing (mind, body) appear to be essentially different:

… on the one hand I have a clear and distinct idea of myself, in so far as I am simply a thinking, non-extended thing; and on the other hand I have a distinct idea of body, in so far as this is simply an extended, non-thinking thing. And accordingly, it is certain that I <that is, my soul, by which I am what I am> really distinct from my body, and can exist without it. (Descartes & Cottingham, 1996, p. 54 [78])

Descartes has different clear and distinct ideas of mind and body and so, for him, they must be distinct. But, the only thing that justifies these ideas is how bodies and his own mind appear to Descartes.

The problem with Descartes’ arguments and distinctions is that they assume that the essential nature of the mind or consciousness appears to, and is accessible by, the subject. In other words, he assumes that we can know precisely what consciousness is by introspecting and determining its properties. Yet we now know that consciousness has properties that aren’t available to introspection. Flanagan raises this point abstractly in responding to Nagel (who’s arguments we will meet below):

Why think that how consciousness seems gets at its real nature? To be sure, the phenomenological aspects of experience are real and require an account. But unless one thinks that the conscious mind is diaphanous, one should not think its real nature is revealed fully by its first-person appearances. (Flanagan, 1992, p. 90)

This is not merely an abstract concern, when we look at the study of consciousness we see that there are many facts about consciousness and its nature which are not available to introspection. For example, humans can typically distinguish more purples than oranges, and the most saturated yellow is brighter than the most saturated blue (Clark, 1993). But this was discovered through experimentation, not introspection.

For reasons such as this introspection alone cannot motivate an argument that consciousness has an essentially different nature than other natural things. Identity theorists (of many stripes) would have it that, contra Descartes, consciousness is spatially extended in virtue of being identical to the activity of spatially extended neural networks. Whether or not it is so extended is an empirical question about the truth of such a hypothesis and is not determinable via introspection, because the relevant property of an experience (being identical to the activity of a neural network) doesn’t appear in introspection.

We can see this concern in Descartes contemporary critics. In their correspondence Princess Elisabeth identifies what has become a textbook objection (e.g. Churchland, 1984) to Descartes metaphysics of the mind. Specifically, she questions how a non-extended (and non-located) substance could affect the body (Descartes & Princess Elisabeth, 1643, p. 1). This is a concern which Descartes doesn’t answer. The conclusion which Princess Elisabeth draws from this worry is:

… I would find it easier to concede matter and extension to the soul than to concede an immaterial thing could move and be moved by a body. (Descartes & Princess Elisabeth, 1643, p. 4)

She is suggesting here that the soul (mind, “I”, self, or most importantly for us, consciousness) could have a nature which is not apparent via introspection. Notice that she is giving us a kind of transcendental inference. Roughly:

1. 1.

Fact to be explained: the mind can move the body (in a reason respecting way).

2. 2.

Hypothesis 1 (Descartes): in virtue of being a thinking, non-extended, thing the mind (who’s essential nature we know via introspection) can move the body in a reason respecting way.

3. 3.

Objection (Elisabeth): nothing non-extended can move something.

4. 4.

Hypothesis 2 (Elisabeth): contra its appearance in introspection the mind is spatially extended and so can move the body.

None of this is exactly correct of course, although it is tremendously impressive given that Descartes frames their discussion with reference to a vague notion of how weight works (recall this is pre-Newton). The point is twofold. First that Princess Elisabeth is employing a kind of transcendental inference. I will do this too, but with the good fortune of more than 370 years of extra scholarship to build from. Second that even Descartes’ contemporary critics were uncomfortable with the idea that that the essential nature of the soul (or mind, “I”, self, consciousness) is given in introspection.

Were it true that introspection gave us knowledge of the complete essential nature of consciousness, then the fact that consciousness appears different to paradigmatically natural things would be significant. But, were this true then we would already have a complete and satisfactory theory of consciousness, for we would all get one simply by introspecting. Clearly there is some hidden nature to consciousness, hidden even from the subject of experience. It is our job as theorists to discover this nature.

Whilst introspection could be a source of hypotheses regarding the essential nature of consciousness, it cannot be the last word on the matter. Further testing of the hypotheses will always be required. More often introspection will be a source of data to be explained. Nowhere else in our studies of the world would we consider it reasonable to conclude that we know the essential nature of something based on a single, fallible, source of evidence. And we should not do so with consciousness.

It seems then that Descartes’ worries aren’t sufficient to motivate concerns that consciousness must be supernatural. Although reasons have been added through the twentieth century for worrying that consciousness is supernatural they are all very closely related to the concerns raised by Descartes and all build from it just seeming like consciousness must be different to natural things, although the specific purported differences are not always those expressed by Descartes. For example, Nagel proposed that we can’t know that consciousness is a natural phenomenon because knowing all that we can know through natural science won’t tell us what it is like to be a bat (Nagel, 1974). Jackson proposed that a person who was prevented from seeing coloured things, but who was never the less able to learn the complete nature of humans who see colour and their interactions with the world, would learn something new on seeing a scarlet macaw for the first time. Namely what it’s like to see red, blue and gold (Jackson, 1982). Others, notably Chalmers, proposed that we can imagine zombies which are exactly like us in every natural feature, but who lack experiences (Chalmers, 2002).

All of these classic worries rest on it seeming like consciousness is just different from natural things and knowing about consciousness is just different to knowing about natural things. The purported differences between consciousness and natural things may be different than those supposed by Descartes. For example, Nagel’s concern is not that consciousness isn’t spatially extended, but rather that in taking an objective “scientific” perspective on a bat, we leave behind how things appear to the bat from its subjective point of view (Nagel, 1974). For Jackson it is that, intuitively, consciousness is not knowable in the same way as other things (Jackson, 1982). This kind of reasoning is used to suggest that consciousness poses us a uniquely “Hard Problem” or leaves an explanatory gap. Whatever we can come up with in science won’t tell us what it is like to undergo an experience and so there must be more to consciousness than is knowable by doing science.

In contemporary literature it is often assumed that the Problem of Consciousness is a “Hard Problem” which is best understood with reference to Chalmers’ worries about what makes consciousness Hard:

What makes the hard problem hard? Here, the task is not to explain behavioral and cognitive functions: even once one has an explanation of all the relevant functions in the vicinity of consciousness – discrimination, integration, access , report, control – there may still remain a further question: why is the performance of these functions accompanied by experience? Because of this, the hard problem seems to be a different sort of problem, requiring a different sort of solution. (Chalmers, 2002, p. 2)

Chalmers limits himself here a bit by talking of explaining only functions that seem related to consciousness, but the point can be made more generally: no matter what we know about the natural features of a conscious system (a person) we don’t know why those features are “accompanied” by consciousness.

Despite attempts by myself and Elizabeth (Carruthers & Schier, 2017) to find (non-question begging) arguments that consciousness must pose a problem like this, the basis for Chalmers’ assertion is just a raw intuition. Consciousness is, it is supposed, just a different sort of thing than what can be explained with reference to natural things like being able to discriminate stimuli, or brain structure or whatever else we might think is related to consciousness. In other words, the “Hard Problem” like Descartes’ concerns, builds into the problem of consciousness the supposition that consciousness is a supernatural phenomenon. The basis for the intuition underlying this supposition is that when we (or at least when Chalmers, or Descartes, or whoever) looks inward, that consciousness just seems to be a different sort of phenomenon to paradigmatically natural phenomenon. But, as discussed above, this only works if we think that we can know (all of) the essential nature of consciousness via introspection. This is something we have no reason to think is true.

Too much ink has been spilt on these issues and as I said above, I take it that the rest of this book (like many others) is an existence proof against such concerns that consciousness is necessarily a supernatural phenomenon and related concerns about the possibility of a science of consciousness. Nonetheless I wanted to remind us of these classic concerns in order to contrast them with the Real Problem of Consciousness, that is, the problem of explaining experiences, and why this problem is so difficult.

Some readers will no doubt find it frustrating that I am not providing detailed arguments against things like the Hard Problem, the explanatory gap and the like. In a way I’ve said little more than I’m not taking those problems as my starting point. What I have had to say on these issues is available elsewhere (specifically Carruthers & Schier, 2017). I don’t want to repeat the arguments here, or remind everyone of the sorts of objections already present in the literature, because I think the assumption that consciousness poses a special kind of problem or must be a supernatural phenomenon has been granted too much power in the literature. The power these problems have is too great because there is no argument that consciousness is like this, simply a bunch of intuitions (often involving unimaginable scenarios as intuition pumps) that it must be. The power these problems have is also too great because it gets in the way of actually progressing on the Real Problem of consciousness. We don’t need to grant these versions of the problem any special power in defining our projects, we don’t have any good reason to grant them any such power and we have good reason not to grant them such power (the essential nature of consciousness is hidden even from introspection), so let’s not. Where to next? Why is the Real Problem of consciousness a particularly difficult problem?

1.3 Difficulties with the Real Problem of Consciousness

In contrast to some traditional views mentioned above I do not think the Real Problem of Consciousness is that consciousness is somehow a supernatural phenomenon. Rather it is just the problem of explaining experience. There are, none-the-less, serious difficulties in obtaining the right kinds of evidence to develop and test such explanations. Some of these will turn out to have important implications later in the book, and the issue of how confident we ought to be in particular ways of measuring consciousness is an issue which we will repeatedly return to. So, what are the difficulties that plague progress on the Real Problem of Consciousness?

In general terms, the worry with attempting to solve the Real Problem of Consciousness is obtaining convincing evidence regarding the occurrence and manipulation of particular experiences. How do we know precisely what a subject is experiencing? This is reminiscent of the traditional “problem of other minds”, but it is not quite the same. The problem here doesn’t require any radical skepticism about whether or not we can know if others are conscious or not, but rather requires us to deal with evidence about consciousness which is, at least sometimes, badly unreliable or potentially invalid. This problem began to rear its head above. I rejected the traditional problems of consciousness because they rely on the unjustified assumption that introspection gives us knowledge of the complete essential nature of experience. But, one reason to doubt that introspection can reliably give such knowledge is that subjects are often wrong about the nature of their experiences. How are we to gain evidence about what experiences a subject is having if we can’t trust their introspective reports? If we can’t get this kind of evidence; how are we even supposed to start studying consciousness?

In the latter part of this book I’ll argue that this worry has deep implications. It doesn’t lead to skepticism or to the conclusion that consciousness is a supernatural phenomenon, but it does speak to the nature of consciousness. For now, let’s have a look at some examples so we can be suitably stressed.

1.3.1 Validity

The real problem of consciousness faces two deep empirical problems. First, how do we get a measure of experience that is valid, and that we know is valid? Second, how do we get a measure that is reliable, and that we know is reliable? “Validity” here is not the same as the notion of “validity” which applies to deductive arguments. Rather, a valid measure is one which measures what we want it to and a reliable one is a measure which works consistently. It is standard in psychology to worry about getting measures which meet these criteria for any mental process or disposition, but the problems are particularly difficult for consciousness.

Issues of validity raise their head as soon as we start to ask people what they can see. As it turns out it is extraordinarily difficult to know if someone is reporting what they see or if they are reporting what they think they should see. Typically, people report that they are conscious of a lot of visual detail and that their visual experiences are coloured to the edge of the visual field. But there is reason to doubt this. The study of phenomena such as change blindness (Simons & Levin, 1997) suggest that people don’t see as much as they think they do. In a typical change blindness task a subject watches a scene which undergoes a large change. For example, one might change the white line on a road in a city scene from dashed to solid and back. Simply distracting a subject’s attention very briefly (in a manner reminiscent of the magician’s sleight of hand) can blind subjects to seeing the change. It is not a big distraction that is needed, all the experimenter need is to briefly take the subjects’ attention to another part of the scene. You can experience this for yourself thanks to the generosity of teams lead by O’Regan and Wiseman at: http://nivea.psycho.univ-paris5.fr/Mudsplash/Nature_Supp_Inf/Movies/Movie_List.html and https://www.youtube.com/watch?annotation_id=annotation_262395&feature=iv&src_vid=voAntzB7EwE&v=v3iPrBrGSJM.

A favourite example purporting to show that we are not conscious of as much as we think we are comes from Dennett (1991). This example is so easy to replicate that given minimal resources you can do it yourself right now. All you need is a well shuffled deck of playing cards. Stare at a point on a wall in front of you. It is important that you continue to stare at this point throughout the entire demonstration. Without looking, randomly select a card and hold it out to one side at arm’s length. Gradually move it toward the centre of your vision. At what point can you see the colour and number on the card? The typical finding is that it is only about 2 or 3 degrees[4] from the point one is looking at that these features become visible (Dennett, 1991, p. 54). The reason for this is to do with the nature of photoreceptors outside of the fovea on the retina and need not concern us here. What I wish to draw attention to, however, is that on first experiencing this demonstration most people seem surprised (Dennett, 1991, p. 68). Pre-theoretically, we expect to be able to discriminate objects easily when they are presented in our peripheral vision. Dennett suggests, and I agree, that this expectation is based on a folk-theoretical belief that vision presents us with a relatively uniformly clear and coloured world in which objects are easily distinguished. But, as this simple demonstration shows, as do other more rigorous experiments, e.g. (Brooks, Yates, & Coleman, 1980), this is at best only true of the foveated world, and even then with some exceptions (Caplovitz, Fendrich, & Hughes, 2008).[5]

Why do we believe this is true of our peripheral vision? We can speculate on many possible reasons for this. One reason might be that things we use as public representations of what we see, e.g. photographs or videos, are somewhat like this. There may be a misbegotten analogy between visual depictions and visual experience. Another more universal proposal comes from Schwitzgebel (2008, p. 255) as well as Dennett (1991, p. 68) who suggests that objects in our peripheral vision appear distinct and coloured because they are when we look at them. Whenever one looks to see what object is in one’s periphery one finds it clear, distinct and coloured. As such we tend to assume that we always experience those objects as such.

But, is this conclusion mandated by the facts? It is not, for the interpretation of the facts given rests on an assumption that visual experience is constructed narrowly in time from visual input as it is now. An alternative approach is to suppose that visual experiences are not simply constructed from a narrow window of what enters the eyes now (or a couple of hundred milliseconds ago), but is instead built up over an extended period of time, constructing a more detailed representation of the visual scene by combining information from a sequence of fixations between saccades (rapid, unnoticed eye movements). In viewing a scene the focus of our eyes (what is foveated) is moved rapidly from one part of the scene to another. If the information from each fixation is not lost, but rather maintained and used to build a detailed representation of the scene which we experience, then there is a sense in which we are right that our visual experiences are detailed and coloured at the periphery.

Well this sort of view seems encouraging, and indeed detailed versions of such views exist in accounts of “visual memory” (Baddeley 1992). But, how then are we to explain the fact that the periphery still seems coloured even when we fixate on one point for a long time? Why don’t we notice big changes to scenes even when our eyes are allowed to move?

I’m not wanting to solve these issues. There are huge literatures on change blindness, foveation, visual memory and the like which I invite you to enjoy. What I want you to take from this is that it is very difficult to know whether or not we can trust subject’s reports about their own experiences. This is not to say that subjects are always, or even often, wrong about what they experience, but rather that knowing whether a report is an accurate reflection of what a subject is experiencing is one of the big challenges that faces the Real Problem of Consciousness. We need valid measures of consciousness in order to gain evidence about it. It seems that, at least sometimes, we can’t assume that a subject simply reporting their experience is a valid measure. In the following chapters I will return to worries like this for the kinds of body experiences being discussed. In later chapters one version of this worry, the problem of distinguishing accurate reports from confabulations will have important implications.

1.3.2 Reliability

Schwitzgebel has made much of the unreliability of introspective reports (his concerns are brought together in Schwitzgebel 2011). Many of his concerns revolve around instances in which subjects are apparently (or obviously) wrong about their experiences. These examples suggest that reports about experiences aren’t, or aren’t always, valid measures of experience. Some of his examples suggest that reports about experiences are also unreliable in the narrower sense introduced above. Sometimes our reports of experience vary wildly, both between individuals and in the same individual at different times, in a way that suggests that it is producing reports of experiences themselves which is unreliable.

One example which helps us get a sense of the unreliability of report as a measure of consciousness is the classic ‘inattentive driver’ (Schwitzgebel, 2011, pp. 91–92). This is a common experience, when driving a familiar route home your mind may wander to any number of topics… pizza, an unpleasant football player in your local competition, salt and pepper tofu. Whilst wandering through these topics you suddenly notice that you’re much closer to home than you anticipated. Were you conscious of the traffic, the lines on the road and red lights on the way? Have you now forgotten them? Perhaps you were only conscious of your train of thought and merely perceived the road unconsciously. Alternatively, perhaps you were peripherally conscious (a bit conscious) of the road and traffic, but you never attended to it. A variety of examples are commonly used to get to this issue of whether or not we seem to experience things we’re not attending to. What is it like to suddenly notice that the refrigerator has stopped humming when you were deeply engrossed in something on TV? Before I mention it… are you conscious of the pressure of the seat on your back? Your feet on the ground? Different people, including different consciousness researchers, are inclined to different answers (see Schwitzgebel, 2011, pp. 92, 95).

Schwitzgebel has tried to get a bit more of a handle on whether or not we experience things we’re not attending to using an approach of “immediate retrospection” or experience sampling. He gave subjects a beeper to wear, which sounded at long intervals. When it sounded the subject’s task was to record a report of what they were experiencing immediately before the beeper sounded. Subjects were asked to report on (i) everything they were experiencing, (ii) all of their touch sensations, (iii) all of their visual sensations, (iv) whether they were experiencing touch in their left foot or (v) whether they were experiencing anything in the far right of their visual field (Schwitzgebel, 2011, pp. 100–101).

Now there is much interesting material to discuss given this method of producing reports of experience. What matters for us here is the variation in the reports given. For example, those in groups i, iii and v (those who were invited to report visual experiences) typically reported that they were seeing something just before each beep, but some subjects sometimes reported not seeing anything. This was the case even when they were asked to distinguish between the seeing blackness that comes with closed eyes and seeing nothing (Schwitzgebel, 2011, p. 103). There was variation within participants as well as between them. For example, some of those asked to report on their experience of their left foot before the beeps reported tactile sensation in around half of their reports (Schwitzgebel, 2011, p. 103).

These are instances of a kind of unreliability of report as a measure of consciousness. When asked about the same kind of situation people are inclined to prefer different descriptions of that (purported) experience. The same measure, report, gives us different descriptions of what is experienced for what is purportedly the same type of experience at different times in different subjects. Which description is right? Are all of them? Perhaps there is variation in how subjects experience such cases? Perhaps only one of the descriptions is right and at other times people are wrong about what the experience is like—there is plenty of room for errors of ‘memory’ here.

Again I’m not going to solve these worries here. The point is that this kind of variation, variation which seems to make report an unreliable measure, is something which poses a challenge for the Real Problem of Consciousness. Unreliability of measures, like worries about validity introduced above, are what makes doing a science of consciousness so very difficult. These are not insurmountable problems and we will meet a variety of ways of managing them along the way, from simple hacks like grouping experiences into types based on common features in reports, to more scientifically robust approaches such as providing controls for the accuracy of reports and looking for converging measures. For now the point is to get our heads around the Real Problem of Consciousness. The Real Problem is not the Hard Problem or explanatory gap, nor even that consciousness seems like it must be, somehow, supernatural. The Real Problem is the problem of explaining experiences when there are deep and difficult questions to ask about how we can measure experiences for the purposes of developing theories. When are our purported measures valid? How are we to understand instance when they are unreliable? That is what makes the Real problem so difficult.

1.4 Conclusion

In this chapter, I’ve tried to pick out what the Real Problem of Consciousness is and how it is different from some traditional worries popular in the tradition of analytic philosophy. I want to try and explain consciousness and will not assume that it is supernatural. That said I must be honest about how difficult it is to get good evidence about what subjects’ experience. The next thing to do is just to get on with the job. Let’s pick a type of experience and see if it can be explained.

References

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Brooks, B., Yates, J., & Coleman, R. (1980). Perception of images moving at saccadic velocities during saccades and during fixation. Experimental Brain Research, 40(1), 71–78.Crossref

Caplovitz, G. P., Fendrich, R., & Hughes, H. C. (2008). Failures to see: Attentive blank stares revealed by change blindness. Consciousness and Cognition, 17(3), 877–886. https://doi.org/10.1016/j.concog.2007.08.006.CrossrefPubMed

Carruthers, G., & Schier, E. (2017). Why are we still being hornswoggled? Dissolving the hard problem of consciousness. Topoi, 36(1), 67–79. https://doi.org/10.1007/s11245-014-9266-3.Crossref

Chalmers, D. J. (1995). Facing up to the problem of consciousness. Journal of Consciousness Studies, 2(3), 200–219.

Chalmers, D. J. (2002). Consciousness and its place in nature. In D. J Chalmers (Ed.), Philosophy of mind: Classic and contemporary readings. Oxford: Oxford University Press.Crossref

Churchland, P. M. (1984). Matter and consciousness. Cambridge: MIT Press.

Clark, A. (1993). Sensory qualities. Oxford: Clarendon Library of Logic and Philosophy.

Dennett, D. C. (1987). Cognitive wheels: The frame problem of A.I. In Z. Pylyshyn (Ed.), The robot’s dilemma. Albex.

Dennett, D. C. (1991). Consciousness explained. New York: Penguin Books.

Descartes, R., & Cottingham, J. (1996). René descartes: Meditations on first philosophy: With selections from the objections and replies. Cambridge: Cambridge University Press.Crossref

Descartes, R., & Princess Elisabeth. (1643, 1644/2009). Correspondence between Descartes and Princess Elisabeth (J. Bennett, Trans.). EarlyModernTexts.com. Retrieved from http://www.earlymoderntexts.com/pdfs/descartes1643.pdf.

Flanagan, O. J. (1984). The science of the mind. Cambridge: MIT Press and Bradford Books.

Flanagan, O. J. (1992). Consciousness reconsidered. Cambridge: MIT Press.

Jackson, F. (1982). Epiphenomenal qualia. Philosophical Quarterly, 32I, 127–136.Crossref

Levine, J. (1983). Materialism and qualia: The explanatory gap. Pacific Philosophical Quarterly, 64(4), 354–361.Crossref

Nagel, T. (1974). What is it like to be a bat? Philosophical Review, 83, 435–450.Crossref

Schwitzgebel, E. (2008). The unreliability of naive introspection. Philosophical Review, 117(2), 245–273.Crossref

Schwitzgebel, E. (2011). Perplexities of consciousness. Cambridge: MIT Press.

Simons, D. J., & Levin, D. T. (1997). Change blindness. Trends in Cognitive Sciences, 1(7), 261–267.Crossref

Footnotes

1

On reading this claim that the mind is a representational/computational device some readers may expect extensive discussion of a currently fashionable position known as “Bayesianism.” Bayesianism offers one possible formalism to Helmholtz’s early description of perception as being the output of unconscious inference. Roughly the formalism states that the posterior probability of a percept is proportional to the prior probability of the percept (the probability that the world is in the perceived state before being perceived) times the likelihood of the percept (the probability that the state of the world would cause the current sensory input). Advocates of this position hold that what we perceive is the state with the highest posterior probability. However, this approach fails to offer a testable alternative to the account considered here.

If Bayesianism is taken as more than a mere description of input/output relations, i.e., as a claim about what computations are actually performed by the mind, we see it immediately runs afoul of the frame problem—i.e. the problem of determining what needs to be represented to perform a particular cognitive task and keeping those representations to a manageable load for a finite computational device (e.g. Dennett, 1987). Taken literally, any possible state of the world with a non-zero probability of causing a particular sensory input would have to be computed and almost all rejected before anything could be perceived.

Worse, however, is the reliance on the “priors”, i.e. the probability that the world is in a particular state prior to being perceived. Such priors are purportedly “learned” through experiencing the world. Again, the frame problem is a problem here, there is an infinite number of states the world could be in with non-zero probabilities. Still, even if advocates could arbitrarily modify the formalism such that only states with a probability above some cut of score are actually represented, the value of the priors is too under-constrained to do any explanatory work. Whatever a subject perceives we can adjust the value of the prior in the formalism such that what they actually perceive turns out to be the state with the highest posterior probability. Without the ability to determine what priors are independently of the percept we are trying to explain, Bayesianism remains untestable.

2

Many thanks go to Gerard O’Brien for this very helpful phrasing.

3

I am using here the 1996 version of Cottingham’s translation from Latin, which also includes Cottingham’s own scholarship. I will occasionally add in parentheses some of Cottingham’s translation from the French version as this will aid our understanding.

4

As a rough guide 1 degree is approximately the angle subtended by a point either side of your thumb nail held at arm’s length.

5

Now of course in the normal case our eyes saccade constantly allowing us to build a much more detailed visual representation than is possible from staring at a fixation point. This makes the area of clear vision significantly larger than the 2–3 degrees observable in a fixation task. This doesn’t affect the central Dennettian claim that periphery is not clear and coloured in the way that we would typically assume. Nor do we typically reflect on how much moving our eyes is necessary for seeing the way we do.

© The Author(s) 2019

Glenn CarruthersThe Feeling of Embodimenthttps://doi.org/10.1007/978-3-030-14167-7_2

2. The Feeling of Embodiment: Our Target of Explanation

Glenn Carruthers[1]

(1) School of Psychology, Charles Sturt University, Port Macquarie, NSW, Australia

Glenn Carruthers Email: gcarruthers@csu.edu.au

This chapter makes use of substantially altered text previously published as: Carruthers, G. (2008, 2009, 2013).

2.1 Introduction

In this chapter, I introduce the feeling of embodiment. The feeling of embodiment, or the experience of oneself as one’s body, as me

, is what I am trying to explain in this book. I begin by pumping some intuitions about the feeling to give us a sense of what this feeling is and how it is important for being able to distinguish ourselves from the rest of the world. I will also introduce some experimental and pathological alterations to the feeling of embodiment as seen in the rubber hand illusion, the delusion of somatoparaphrenia, and body integrity identity disorder. This will help to distinguish the feeling of embodiment from the sense of ownership of the body. Throughout this chapter I will return to the Real Problem of Consciousness. We will begin to get a sense of how difficult it is to be confident that a report or set of reports provides a valid and reliable measure of the feeling of embodiment. However, we will see that through the use of well-designed questionnaires, corroborative measures and by grouping reports into types that we can make progress on the Real Problem.

2.2 The Feeling of Embodiment: A First Pass

Before moving on to the more recently discovered facts, I’d like to give you a sense of what I mean by “the feeling of embodiment” by pumping some intuitions about the experience using easily imaginable scenarios. Look around. If you are in an office you will see desks, chairs, whiteboards and the like. If you are outside you will see buildings, trees, grass and (if you’re lucky) swans and ducks. You can also be aware of these via your other senses. One problem will never arise for you. You won’t confuse yourself with these objects. Someone bursting through your office door may lead to a variety of problems. But, baring pathology, one problem would never arise. You would never confuse yourself with that person. Similarly, we don’t confuse our body parts with those of others. This may be the most fundamental aspect of your sense of self: the feeling of being a distinct entity from other objects and persons (Eilan, Marcel, & Bermudez, 1995, p. 9).

Now it might sound funny to think of this problem, the problem of distinguishing yourself from other people and things, as a problem at all. It’s just obvious what you are and what is something else, right? Typically this isn’t a problem for us, at least not a conscious problem. You don’t need to stop and think and work out what you are whenever it might be relevant. But this is something that needs to be computed by your mind. It is not simply given to you what you are, although it sure seems that way. The reason it seems like the knowledge of where you end, and the world begins is just given to you, as if by magic, is that you have, ready at hand, an experience of embodiment whenever you need it. But this experience does not come from nowhere, it is produced by you unconsciously. You don’t experience how this is done, all you experience is the end result, the feeling of embodiment.

Along with this feeling of being a distinct entity, comes the recognition that you have your own perspective on the world (Damasio, 1994, p. 238). You experience your body “from the inside” (Martin, 1995, p. 267). That is, you seem to be contained or bounded within your body. Hence anything outside of your body seems distinct from you and your point of view is from within your body. If you’re like me it may be that very often you seem to be looking out on the world from just behind your eyes, although the occurrence of such an experience will be task and culturally dependent. There are other ways in which we seem to have a spatial perspective from within our bodies. If you were to get kicked in your right shin there would not be a diffuse experience of pain, nor would it hurt your left elbow, it would hurt your right shin (Martin, 1995, pp. 268–269). Typically, when something impacts on your boundaries you know (about) where on your boundary that impact occurred (Damasio, 1994, pp. 232–233). In generating a sense of what and where your boundaries are you are able to generate your own perspective. This is another component of the sense of embodiment.

2.3 Sense of Ownership Versus Feeling of Embodiment I: Asomatognosia and Somatoparaphrenia

So much for trying to get an intuitive feel for this feeling. There’s already a bit to argue about from these first gestures at our explanatory target. How are we to characterise this feeling and its relationship to other kinds of self-consciousness ? Well, I’m going to have to beg your indulgence, for the next few pages, to suffer what looks like a fairly bland terminological dispute. It is a dispute, however, which I find helpful as it will ultimately give us some grounding in existent empirical data for describing the feeling of embodiment. It will also allow us to begin to make contact with others who have attempted to explain this feeling, or, as they call it, the sense of ownership.

de Vignemont (2007) attempts to provide an explanation of the feeling that one’s body is one’s own; the feeling that this body, which I experience sensations in and experience proprioceptively, is my body. She calls this the “sense of ownership” of one’s own body (de Vignemont, 2007, p. 427). One problem de Vignemont faces is the specification of the sense of ownership. This may simply be because the sense of ownership is hard to discuss. This would be the case if the sense is, as she suggests, “dim and elusive” (de Vignemont, 2007, p. 430). However, we will see that there is a problem with de Vignemont’s description of the phenomenology which makes it difficult to know just what is being explained by her model. I suggest that de Vignemont’s account is best taken as an explanation of the sense of embodiment.

de Vignemont begins her account:

The body has an ambiguous status, as it seems to be both what we are and what belongs to us. The study of the relationship between the body and the self raises several distinct issues… there is the question of the sense of ownership: on which basis do I feel this body as my own? In this paper, I shall focus on [this] question by investigating the conditions of possibility of the sense of ownership of one’s body. (de Vignemont, 2007, p. 427)

Here de Vignemont is distinguishing two different ways we can experience our bodies. The first is that I can experience the body as what I am. I experience my body as me

. This is the sense of being an embodied self. The second is the experience of the body as a thing that belongs to me. I experience my body as mine

. In this second case, rather than experience my body as what I am, I experience it as a thing which I attribute to myself. What we see here is two different uses of the term ‘self-consciousness ’. We can use the term to refer to experiences that represent a self qua a self, e.g. as a subject or agent, or we can use the term to refer to experiences which represent properties which are attributed to that self. In this context de Vignemont seems to take this second type of experience as her target when she says her question is “on which basis do I feel this body as my own?” (de Vignemont, 2007, p. 427).

This description is problematic for a variety of reasons which I’ll consider over the next two sections. First, let’s get a superficial worry out of the way. In self-consciousness research there is another class of experiences named ‘the sense of ownership’. These experiences are experiences of ownership over actions, that is, the experience that I am the thing who is moving (which stands in contrast to the sense of agency, which is the sense that I am causally responsible for or in control of the action) (Gallagher, 2000). If for no other reason than to make our lives easier we should favor the alternative terminology, such that there are not two technical meanings of the phrase ‘sense of ownership’ within a single literature.

Now for some more substantive worries. To generate and support her model de Vignemont begins with a consideration of what she calls ‘asomatognosia’ and the delusion of somatoparaphrenia. When we look at the reports of those suffering these disorders it seems they are better understood as involving a deficit in the feeling of embodiment than a deficit in the sense of ownership. So, it seems to me that de Vignemont is de facto providing an account of the sense of embodiment and its deficits, rather than the sense of ownership.

de Vignemont characterizes ‘asomatognosia’ as the denial of ownership of a limb. That is, patient’s claim that their arm is not their own (de Vignemont, 2007, p. 428; Feinberg & Keenan, 2005; Feinberg, Roane, & Ali, 2000; Wise, Malik, & Husain, 2010). Commonly this “denial of ownership” of a limb is accompanied by the delusional belief that the limb is someone else’s limb. This elaboration of asomatognosia is often referred to as ‘somatoparaphrenia’ and takes the form of a delusion (Baier & Karnath, 2008; Bottini, Bisiach, Sterzi, & Vallar, 2002; de Vignemont, 2007, p. 428; Miura et al., 1996; Suzuki et al., 2000). There is, however, at least one case in which the patient experiences the target arm as not their own (suggesting a deficit in the sense of embodiment), but does not delusionally attribute the arm to another (Wise et al., 2010). This case is also unusual in that it is the right arm which is targeted following left hemisphere damage, the reverse pattern is more common. In some cases, the denied limb is taken to be dead or is considered some other inanimate object (as in Feinberg & Keenan, 2005, pp. 667–668; Sacks, 1986, pp. 53–56). In these cases, patients may or may not have an opinion as to where their real limb is. Although this disorder is often associated with personal hemispatial neglect (Aglioti, Smania, Manfedi, & Berlucchi, 1996), neglect does not explain the disorder (Moro, Zampini, & Aglioti, 2004).

Note this isn’t always how the term ‘asomatognosia’ is used. Some (e.g. Arzy, Overney, Landis, & Blanke, 2006; Gold, Adair, Jacobs, & Heilman, 1994; Paysant, Beis, Le Chapelain, & Andre, 2004; Pearce, 2007; van Stralen, van Zandvoort, & Dijkerman, 2011) use the term to refer to the absence of the limb from awareness, thus tying the denial of ownership of a limb to hemispatial neglect (as noted by Peru & Pinna, 1997). However, it is clear that the denial of ownership of a limb is not due to neglect per se. Whilst the denial of ownership is commonly associated with hemispatial neglect (Vallar & Ronchi, 2009, p. 545), this is unlikely to explain the disorder as moving the affected limb into non-neglected space does not affect patients’ attributions of ownership (Moro et al., 2004). It is therefore helpful to have a term to pick out the denial of ownership of a limb without building neglect into its definition. This seems to be the sense in which de Vignemont is using ‘asomatognosia’.

The definitional matter is confused further by the delusional belief that the denied limb is someone else’s limb. This seems to involve more than the denial of ownership of the limb, namely the attribution of that limb to someone else. As I said above, this condition is often referred to as ‘somatoparaphrenia’ (Bottini et al., 2002; Coltheart, 2005; Coltheart, Langdon, & McKay, 2007; Miura et al., 1996; Suzuki et al., 2000). However, it is also sometimes called ‘asomatognosia’ (Meador, Loring, Feinberg, Lee, & Nichols, 2000). Daprati and colleagues use ‘somatoparaphrenia’ to refer to any delusion “in which the affected limb is involved in bizarre illusory or confabulatory ideas” (Daprati, Sirigu, Pradat-Diehl, Franck, & Jeannerod, 2000, p. 447), with the absence of the limb from awareness and the attribution of the limb to others being the most “severe” case (Daprati et al., 2000, p. 478).

For the purposes of this book I will follow de Vignemont’s and others (e.g. Baier & Karnath, 2008) use and take ‘asomatognosia’ to refer to the denial of ownership of a limb simpliciter and ‘somatoparaphrenia’ to refer to the attribution of the limb to someone else.

With the terminology defined, the question arises: do these disorders involve a deficit in a feeling of ownership? Patients suffering from asomatognosia or somatoparaphrenia don’t just feel like the limb doesn’t belong, it seems that they feel it is not a part of them, their self, anymore. They can be so horrified by the limb that they try to get rid of it (as in Sacks, 1986). They can feel this and still attribute the limb to themselves in some sense:

Shirley:

It took a vacation without telling me it was going. It didn’t ask it just went.

Feinberg:

What did?

Shirley:

My pet rock. [She lifted her lifeless left arm with her right arm to indicate what she was talking about.]

Feinberg:

You call that your pet rock?

Shirley:

Yeah.

Feinberg:

Why do you call it your pet rock?

Shirley:

Because it doesn’t do anything. It just sits there.

Feinberg:

When did you come up with that name?

Shirley:

Right after it went plop. I thought I’d give it a nice name even though it was something terrible.

Feinberg:

Do you have any other names for it?

Shirley:

Her. She belongs to me so she’s a her. She’s mine but I don’t like her very well. She let me down.

Feinberg:

In what way?

Shirley:

Plop plop rock nothing. I was on my way home out the door and then she went and did this [pointing to her left arm]. She didn’t ask if she could [shaking her head back and forth]. I have to be the boss not her, [she said pointing to her left arm]. (Feinberg & Keenan, 2005, p. 667, emphasis added)

This seems to be more than a failure of self-attribution, indeed there is a sense in which Shirley is attributing her denied limb to herself (“she’s mine”). The denied limb is something she owns, but it is not her. This patient seems to experience herself as not properly embodied in the affected limb anymore. She feels that the limb is not a part of her anymore; she feels that she has lost a part of herself, not an object she owns. As such it seems that much the data de Vignemont uses bears on the issue of the sense of being embodied but not the attribution of the body to oneself.

This content seems to reflect more closely an experience of the self as embodied and as the agent of bodily actions than of the body as a thing that is mine. In other words, it seems to be an experience of the body as me rather than mine. Let us note that asomatognosia (as de Vignemont uses the term) and the delusion of somatoparaphrenia both seem to involve a deficit in the sense of embodiment, to wit, the sense of the body as me .

Here one must acknowledge the Real Problem of Consciousness. Just how trustworthy are the reports of these patients? They seem to be reliable, in that patients describe similar experiences over time, but are they valid measures of what is being experienced?

Some have worried that patient reports may not accurately represent their experiences in cases of somatoparaphrenia. Instead positing that somatoparaphrenia is a kind of confabulation used by patients suffering anosognosia for hemiplegia to explain away their paralysis. I will have more to say on anosognosia for hemiplegia in the next chapter, for now it is enough to know that this is a delusion held by some patients who have been paralysed or severely weakened by a brain injury. The delusion leads patients to assert that they are not paralysed or weakened, when, in fact, they are. Patients suffering from somatoparaphrenia are typically also suffering anosognosia for paralysis of the same limb, that is the targeted limb is paralysed and the patient does not believe they are paralysed (Bisiach, Rusconi, & Valler, 1991, p. 1029). Many patients with anosognosia for hemiplegia also attribute ownership of the limb to someone else when asked. For example, 11 of 12 patients in Baier and Karnath’s study (2008) did so. This is also common when anosognosia is induced by deactivation of the right hemisphere. This is called the ‘Wada’ test. This test is used to assess the brain lateralisation of language in patients prior to surgery for severe epilepsy and involves the use of chemicals to deactivate one hemisphere of the brain. This also causes temporary paralysis of the side of the body contra-lateral to the deactivated hemisphere; that is deactivation of the right hemisphere causes left sided paralysis. Meador and colleagues found that when asked about the paralysed arm, 88% of patients denied paralysis with a majority, but not all, also attributing the paralysed arm to an experimenter (Meador et al., 2000). There are also cases in the clinical literature of anosognosia without somatoparaphrenia (Marcel, Tegner, & Nimmo-Smith, 2004, p. 22). Could somatoparaphrenia be a confabulation produced by some patients to explain why they can’t move a limb (Coltheart, Langdon, & McKay, 2011, p. 287)?

Joseph (1986) considered somatoparaphrenia to be a kind of confabulation on par with the kinds of confabulation used by those suffering anosognosia for hemiplegia to explain away their inability to move. This seems plausible when we consider reports from such patients. Joseph (1986) opens with this discussion:

Ex:

“Give me your right hand!” (Correct.) “Now give me your left!” (The patient presented the right hand again. The right hand was held.) “Give me your left!”

(The patient looked puzzled and did not move.) “Is there anything wrong with your left hand?”

Pt:

“No, doctor.”

Ex:

“Why don’t you move it, then?” (The left hand was held before her eyes.)

Pt:

“I don’t know.”

Ex:

“Is this your hand?”

Pt:

“Not mine, doctor.”

Ex:

“Whose hand is it, then?”

Pt:

“I suppose it’s yours, doctor.”

Ex:

“No, it’s not; look at it carefully.”

Pt:

“It is not mine, doctor.”

Ex:

“Yes it is, look at that ring; whose is it?”

Pt

“That’s my ring; you’ve got my ring, doctor.”

Ex:

“Look at it-it is your hand.”

Pt:

“Oh, no doctor.”

Ex:

“Where is your left hand then?”

Pt:

“Somewhere here, I think.” (Making groping movements near her left shoulder.) (Joseph, 1986, pp. 507–208)

Here the denial of ownership could plausibly be an attempt to explain why the patient fails to move the arm. One cannot simply will another’s arm to move. Indeed, in this case the denial of ownership seems to be suggested by the doctor (“Is this your hand?”) as a potential explanation.

The hypothesis that somatoparaphrenia is merely a confabulation produced by the patient to make sense of why they cannot move a paralysed limb is spoken against by cases of spontaneous reports and actions by patients against the limb at onset. Brock and Merwarth (1957) suggest that their patient exhibited odd behaviours towards his left arm, seemingly attempting to avoid it, before questioning elicited the claim that the arm belonged to his daughter. Other patients will throw their limb out of bed in an attempt to be rid of it (Joseph, 1986, p. 515). Aglioti and colleagues’ patient CB first showed signs of somatoparaphrenia when she asked her son to ask doctors to remove “the hand they left in her bed” (Aglioti et al., 1996, p. 293). Several patients first showed somatoparaphrenia by complaining that they are being touched by someone, when in fact their own hand was touching them (Cereda, Ghika, Maeder, & Bogousslavsky, 2002; Prigatano, Matthes, Hill, Wolf, & Heiserman, 2011; Wise et al., 2010). Such patients seem to be acting as though they experience the limb as belonging to another prior to confabulations being provoked by direct questioning.

A similar conclusion is suggested by other evidence. Prigatano et al., (2011, p. 1224) report of a patient who misattributed ownership of her paralysed hand only after she correctly recognised that she was paralysed. That is, this patient experienced somatoparaphrenia only after anosognosia had remitted. Similarly, in Meador and colleagues’ Wada test study, 6 patients (10% of the sample) attributed ownership of their paralysed limb to an experimenter, but nevertheless correctly recognised that they were paralysed (Meador et al., 2000, p. 817). Furthermore, Invernizzi et al. (2013) report the cases of CP and MA who suffered somatoparaphrenia, but who readily acknowledged their paralysis. Indeed, there are other cases of somatoparaphrenia for limbs without paralysis (Beato et al., 2010; Wise et al., 2010), or marked weakness but not complete paralysis (Brock & Merwarth, 1957). Beato and colleagues observed a patient who felt that her right arm did not belong to her yet “no impairment of spontaneous movements of her right arm was observed and she was able to reach and use objects in her right space with her right hand” (Beato et al., 2010, p. 1208).

Somatoparaphrenia does not seem then to be merely a confabulation used to explain away an inability to move. Instead it seems to involve a distinct (but related) disturbance of body awareness (Vallar & Ronchi, 2009). It is likely that misattributions of ownership do reflect a deficit in the sense of embodiment in the denied limb. Somatoparaphrenia thus could be a potentially fertile source of evidence in the attempt to develop and test explanations of the sense of embodiment.

2.4 Sense of Ownership Versus the Feeling of Embodiment II: The Rubber Hand Illusion

We can get a deeper understanding of this distinction with a consideration of the rubber hand illusion. The rubber hand illusion (RHI) is the experience of an artificial body part as being the real body part, most commonly a hand. This illusion was made famous by Botvinick and Cohen (1998), whose single-page report has spawned an industry of research. Their method for inducing and measuring the illusion is still used with only minor alterations. In their study subjects sat with their left arm positioned on a table, behind a screen so that they could not see it. In front of the subject the experimenters placed a realistic life-sized prosthetic hand (made of rubber—hence the name). Subjects were asked to look at the rubber hand whilst an experimenter stroked the rubber hand and the subject’s real left hand simultaneously with matching paint brushes. This is called the synchronous condition. After 10 minutes of such stimulation subjects were asked to complete a questionnaire and their responses were compared to those who, in a similar set up, saw touches on the rubber hand out of time with what they felt (the asynchronous condition).

Subjects gave descriptions of the experience of the rubber hand being their own hand. For example, one subject said: “I found myself looking at the dummy hand thinking it was actually my own” (Botvinick & Cohen, 1998, p. 756). And, bam! Just like that the Real Problem of Consciousness is back to stop us in our tracks. This is a weird set up, why trust the subjects’ reports? Mightn’t the subjects just say something they think is helpful for the experimenters, or report something they think they should experience, rather than what they actually experience? Botvinick and Cohen were concerned about this too, and so attempted to corroborate subjects’ reports with an “objective” measure. Unfortunately, there are problems with the objective measure they chose (called “proprioceptive drift”) which I will discuss in Chapter 4. But, the use of a well-designed questionnaire, the relatively easy reproducibility of the illusion and the corroboration of reports with other objective measures (some we will meet below, some will be discussed in Chapter 4) suggests that such reports are reliable and valid measures of experience.

Consider the questionnaire. The questionnaire asked subjects to affirm or deny 9 statements and asked for any further descriptions of the experience the subjects wished to give (Botvinick & Cohen, 1998, p. 756). Three statements on the questionnaire received consistent positive responses from subjects who underwent synchronous stroking. These were (i) ‘It seemed as if I were feeling the touch of the paintbrush in the location where I saw the rubber hand’; (ii) ‘It seemed as though the touch I felt was caused by the paintbrush touching the rubber hand’; and (iii) ‘I felt as if the rubber hand were my hand’.

Other items referred to experience which a naive subject could plausibly think are altered by the procedure, but which are not, in fact, part of the illusion. These remaining items received consistently negative or widely variable responses. Importantly subjects’ responses to these items did not differ between the synchronous (illusion) and the asynchronous (control) conditions. This variability in responses by question suggests that the positive responses given by all subjects to the above three questions were not the result of mere suggestibility (Ehrsson et al., 2008, p. 3446) or some other bias. Rather they accurately reflected the subjects’ experience during the experiment. However, it is unclear whether or not some subjects’ affirmations of the remaining questions arose due to individual differences in the experience of the illusion or individual differences in suggestibility and other response biases.

It seems then, that we have some reason to trust subjects’ reports, especially their questionnaire responses, in the case of the RHI. So, the question at hand is: what is it like to experience this illusion? In the standard version of the illusion two extraordinary experiences stand out. The first is the feeling of touch coming from the rubber hand, an object with no sensory system whatsoever. The second is the peculiar sense of identification with the rubber hand. This is the sense of embodiment in the rubber hand. I take it that this experience is an experience of the rubber hand as though it is a part of me, that is, as if it is my real hand (Ijsselsteijn, de Kort, & Haans, 2006, p. 455). At the onset of the illusion the rubber hand shifts from being experienced as an object external to oneself to being experienced as a part of oneself. That is the feeling of being embodied in the rubber hand.

This is, of course, not the only way that this experience is described. Often the experience of identification with the rubber hand is described as an experience of ownership over the hand, just as above. This terminology, however, mis-describes the phenomenology of the rubber hand illusion and may lead to confusion with other experiences also named ‘the sense of ownership’. The term ‘sense of ownership’ seems to suggest not that I come to feel that the rubber hand becomes a part of me, but rather that it becomes something that I own; an object external to the self which is then self-attributed. That it is ‘mine’ rather than ‘me’. Describing the rubber hand illusion as an illusion of the sense of ownership is problematic.

The term ‘sense of ownership’ seems to mis-describe the everyday experience of the body as well as the experience of the rubber hand in this illusion. As above and following de Vignemont, this term seems to imply that the hand is experienced as an object external to the self over which a relationship of ownership is claimed. This, I contend, is not the normal experience of one’s body parts. The normal experience of a body part like a hand involves feeling that it is a part of oneself, that is as a part of the self to which properties can be attributed, rather than as a property attributed to the self. As Tsakiris (2010) suggests the rubber hand in the illusion seems to ‘replace’ the real hand. Now, this is a particular class of experience and surely it is not the only way we experience or represent our body parts; however, it does seem to be the experience at stake in the rubber hand illusion. This is suggested by the following sample reports:

Soon you have the feeling the rubber hand is really your hand, you can really feel it being touched.

It soon appeared as if the projection was my own hand, and my own hand was being touched. (Ijsselsteijn et al., 2006, p. 462)

These experiences are better described as a feeling of embodiment in the hand than a feeling of ownership over it. If correct we would expect subjects to treat the rubber hand as a part of the self following induction of the illusion, but not when the illusion is not present. So, what is the extent to which the rubber hand is represented as one’s real hand during this illusion? Is this something subjects say in order to be cooperative in a strange situation, or is the hand treated phenomenologically and functionally as a part of their body? Again, this is a worry about the validity of the questionnaire and spontaneous reports as measures of the sense of embodiment. Some control against suggestibility was provided by the inclusion of extra items in the questionnaire, but whilst these controls suggest that the subjects experience of the rubber hand really is altered in the illusion set up, is this enough for us to know that they are responding based on their sense of embodiment, rather than a sense of ownership? It would be nice if there was additional evidence that suggested these reports are valid operationalisations.

The extent to which subjects treat the rubber hand as a part of their own body is suggested by their reactions to the rubber hand being attacked. Ehrsson et al. (2007) operationalised an anxiety response and anticipation of pain via a differential increase in activity in the insula and anterior cingulate cortex (ACC) as measured by functional magnetic resonance imaging (fMRI). fMRI is a brain imagining technique which records changes in blood flow. When an increase in blood flow to a region of the brain is observed it is inferred that region has recently been more active . Following Botvinick and Cohen’s design (modified for the subjects lying in a MRI scanner, of course), Ehrsson and colleagues attempted to elicit the RHI using synchronous stroking, and used asynchronous stroking as a control (Ehrsson et al., 2007, p. 9828). At times in both conditions an experimenter held a needle in a threatening position near the rubber hand. Subjects were asked to report, non-verbally with a button press, the extent to which they felt the rubber hand was their hand, and how anxious they felt when they saw the needle. It was found that subjects rated anxiety at the presence of the needle near the rubber hand significantly higher during synchronous stroking than asynchronous stroking (Ehrsson et al., 2007, p. 9829). Similarly, there was a greater increase in activity in the ACC and insula at the sight of a needle in the synchronous than asynchronous condition (Ehrsson et al., 2007, p. 9830). This, coupled with the correlation between ratings of vividness of the RHI and anxiety of the subjective rating scale (Ehrsson et al., 2007, p. 9830), suggests that subjects react with anxiety to a rubber hand being threatened during the RHI, but not to a rubber hand in the same location relative to the body when not experiencing the RHI.

This suggests that during the illusion the rubber hand is treated as one’s real hand in a very robust fashion. Not only does it feel like it is a part of one’s body, one is anxious about its well-being as though it is such a part.

Slater, Perez-Marcos, Ehrsson, and Sanchez-Vives (2008) provide further evidence for the extent to which an illusory hand is treated as a part of one’s self by showing that subjects try to counteract unexpected movements of the artificial hand. Slater and colleagues used virtual reality rather than a rubber hand. They produced a virtual image of an arm which appeared to be held out from the subject’s shoulder, parallel to the real arm which sat on a table. An experimenter then touched the subject’s real hand with a wand which controlled an image of a ball, which would touch the virtual hand either synchronously or asynchronously with the touches experienced by the subject. This method reproduced the RHI, with subjects reporting experiences of embodiment in the virtual arm and touch located on the virtual arm following synchronous but not asynchronous stroking (Slater et al., 2008, p. 4). After 5 minutes of such stimulation the virtual arm rotated from flat to perpendicular to the floor and back. During the period of stimulation subjects had muscle activity in their right arm recorded such that there was a record of movement onsets. Importantly Slater and colleagues found that muscle activity indicating the onset of movement during rotation of the virtual arm was more common following induction of the illusion than following asynchronous stroking (Slater et al., 2008, p. 5). This activity was interpreted by the authors as an automatic response to attempt to stabilise the arm against unexpected movement (Slater et al., 2008, p. 5; see also Slater, Perez-Marcos, Ehrsson, & Sanchez-Vives, 2009). Collectively these studies suggest that the rubber hand is treated robustly as a part of the self.

An attempt to further elucidate the experience of the body during the rubber hand illusion has been provided by Longo, Schuur, Kammers, Tsakiris, and Haggard (2008). In seeking a comprehensive description of the phenomenology of the illusion, Longo and colleagues had subjects respond to a 27-item questionnaire following an attempt to induce the illusion with synchronous stroking or an asynchronous stroking control (Longo et al., 2008, p. 982). Using principal components analysis Longo and colleagues discovered four significant groupings of responses following the induction of the illusion using synchronous stroking. These were termed (1) ‘embodiment of rubber hand’ which included items referring to experiences such as the rubber hand appearing to be one’s own, the location of the touch and hand as well as potential agency over the rubber hand (Longo et al., 2008, pp. 982–984); (2) ‘loss of own hand’ which included items referring to the disappearance of one’s real hand as well as being unable to move it (Longo et al., 2008, p. 982); (3) ‘movement’ which included items referring to apparent motion of the real or rubber hand (Longo et al., 2008, p. 986); and (4) ‘affect’ which contained items referring to the interestingness or enjoyableness of the experience (Longo et al., 2008, p. 986). Following asynchronous stroking a further grouping was found termed (5) ‘deafference’ which contained items referring to numbness, pins and needles and an unusually weak experience of the hand (Longo et al., 2008, p. 986). Further analysis of the first component, embodiment of rubber hand, revealed three sub-groupings of responses. These were named (1a) ‘ownership’ which contained items referring to the feeling of the rubber hand being a part of oneself or one’s body, feelings of looking at one’s real hand, and the rubber hand coming to look like one’s own (Longo et al., 2008, p. 986); (1b) ‘location’ which contained items referring to the apparent location of the hand and the touch; and (1c) ‘agency’ which contained items referring to the experience of being able to move or control the rubber hand (Longo et al., 2008, p. 986).

This analysis provides greater insight into and more data driven analysis of experience during the rubber hand illusion than provided by the shorter questionnaire analyses. The first two primary groupings, embodiment of the rubber hand and loss of own hand, are of the greatest interest here. The reason for this is that these factors were affirmed following synchronous stroking but denied following asynchronous stroking, thereby giving us reason to suppose these operationalise the experiences which are altered in the illusion and not merely related to touch (Longo et al., 2008, p. 988). Movement was denied in both conditions, but more strongly in the synchronous stroking condition, affect was affirmed in both but more strongly in the synchronous condition, and deafference was only present as a factor in the asynchronous condition (Longo et al., 2008, p. 988). What this suggests is that during the illusion the rubber hand seems to be one’s own hand, one feels embodied in it, one feels one could move it if one wanted to and one feels touch coming from it. The real hand seems to have disappeared and been replaced by the rubber hand and there is no experience of either the real or the rubber hand moving.

On the whole it seems the rubber hand illusion is best understood as involving a change in the sense of embodiment. Namely during the illusion subjects come to feel as if they are embodied in the rubber hand which they see, rather than their own real hand. Although this illusion will be tremendously important in developing the account of consciousness offered in this book, I don’t want to give the impression that the sense of embodiment only applies to body parts treated individually, rather than the whole body. Let’s have a closer look at the sense of embodiment for the body as an integrated whole.

2.5 Feeling of Embodiment for an Integrated Whole

So far, the clinical and experimental alterations to the feeling of embodiment considered have focused on the feeling for particular body parts. As well as having such experiences for individual body parts, such as hands, it seems we also experience the body as an integrated whole and that when a body part isn’t included as a part of this integrated whole it is experienced as unwanted. Indeed, there are versions of the rubber hand illusion which purport to alter the sense of embodiment for the whole body (Ehrsson, 2007; Lenggenhager, Tadi, Metzinger, & Blanke, 2007). There are also cases where subjects seem to fail to include particular body parts in their feeling of the body as an integrated whole.

Body integrity identity disorder is a relatively recently identified identity disorder that seems to involve a deficit in this sense of the body as an integrated whole (see Brugger, Lenggenhager, & Giummarra, 2013; Giummarra, Bradshaw, Nicholls, Hilti, & Brugger, 2011 for reviews). Body integrity identity disorder, also called xenomelia (Hilti et al., 2013) or simply “amputation-desire” (Romano, Sedda, Brugger, & Bottini, 2015, p. 141), is characterised by a long standing stable desire to amputate one or more limbs (First, 2005) or to become paralysed (Giummarra et al., 2011). The desire is typically specific to a particular limb, but occasionally two limbs are targeted simultaneously (First, 2005, p. 923). Patients are typically able to identify a clear line demarcating the body part they wish removed from the rest of the body (Hilti et al., 2013; McGeoch et al., 2011; Romano et al., 2015, p. 142) and the vast majority of patients report no interest in other kinds of disability (First, 2005, p. 925). It is more common that patients desire the removal of the left limb than the right, and legs are targeted more often than arms (Giummarra et al., 2011; Hilti et al., 2013). There are sex differences in how the desire presents (see e.g. Giummarra, Bradshaw, Hilti, Nicholls, & Brugger, 2012), but these are of little importance here. There is also considerable variation in how much subjects are sexually attracted to those with amputations or paralysis and whether or not they become aroused at the idea of their own disability (Giummarra et al., 2012). The following is a description of a case of a patient who was able to receive their desired amputation:

Tom has always felt that having two arms and two legs made him ‘incomplete’ and that the amputation has, paradoxically, finally made him ‘feel complete’. Although he reports that the main reason for the amputation was to make him ‘whole’, he reports that there is a sexual component to his desire in that he felt more ‘sexual’ while imagining himself as an amputee, and that as an adolescent, he would become sexually aroused when he pretended to be an amputee. He reports that prior to his amputation his left leg did not feel any different from his other limbs nor did he perceive it to be ugly or deformed. He denies that a desire for attention was a motivation for the amputation, noting that he always wears a prosthesis when he is out in public. (First, 2005, p. 920)

In severe cases, this condition leads some patients, like Tom, to seek an amputation. Often by attempting the amputation themselves (e.g. Sorene, Heras-Palou, & Burke, 2006), although in some cases patients have been able to find surgeons willing to perform the surgery (First, 2005, p. 922). Many others explore the possibility of obtaining an amputation.

Most patients reported that their reason for wanting an amputation was to make their body fit their “true” (First, 2005, p. 922) or “ideal” self (Giummarra et al., 2012, p. 39). First reports patients who said things such as: “At some moment, I saw an amputee and I understood that’s the way I should be”; “I feel myself complete without my leg…I’m ‘overcomplete’ with it” (First, 2005). Other patients use emotive terms like “normal” “should be” or “right and comfortable” to describe the state of being paralysed (e.g. cases #2, #3 and #11 in Giummarra et al., 2012). However, it should be noted that only a minority (13%) reported that the limb they desired to amputate “felt like it was not their own” (First, 2005, p. 924). But, this likely reflects the conflict experienced by such subjects who feel like the limb does not belong, but who, neverthe-less know that the limb is a part of their body.

In First’s study, all of those patients who were able to receive an amputation report that the surgery had a positive effect. They report that the surgery removes the desire (typically it does not shift to another limb) and that they feel better about their bodies and identity (First, 2005, p. 926). One subject wrote to experimenters saying: “I’m wondering if I am eligible to participate in this study, because since my amputation I do not have BIID feelings any more” (Blom, Hennekam, & Denys, 2012, p. 3). Epidural anaesthesia administered for child birth has been reported to have a positive effect for one patient desiring paralysis (Giummarra et al., 2012, p. 39). In thinking about their lives those who have managed to achieve an amputation rate themselves as less disabled than those who have not (Blom et al., 2012, p. 3).

What might explain the development of this desire? A clue comes from one patient who noted that conscious effort altered her desire for an amputation:

One female patient who wanted both legs amputated, feeling that her legs did not feel a part of her, reported some decrease in intensity of desires which she attributed to ‘doing body work…focusing on remaining connected when my legs are being touched’. (First, 2005, p. 926)

Consider this in the light of the fact that there is no indication that any of these patients fail to perceive their limb properly nor do they perceive the limb to be deformed or have any delusional beliefs about it (Aoyama, Krummenacher, Palla, Hilti, & Brugger, 2012, p. 104; First, 2005, p. 926). Taken together this data suggests that body integrity identity disorder is a dysfunction of one’s sense of “who one (physically) is” (First, 2005, p. 926). In particular it seems that it is a failure to include the rejected limb in the experience of the body as an integrated whole. Patients with body integrity identity disorder get their boundary wrong, erroneously representing a limb as a needless addition. This patient seems to be able to bring her limbs into the representation of her body with some effort.

It is too early to say for sure why this failure occurs; however, it is possible that the lack of feeling of the body as an integrated whole is a cause. The limb must be represented in part as belonging to oneself as patients don’t show symptoms of somatoparaphrenia, which we met above. They know that the limb is their limb, it is attached to them after all, and they can feel sensations in it, yet they don’t seem to feel embodied in it as they do in the rest of their body.

It seems most likely that body integrity identity disorder involves a failure to include the rejected limb in the experience of the body as an integrated whole. But, this is not certain. It is important to keep in mind that this interpretation is based on the verbal reports of patients. There are several reasons why someone might report that a limb is not ‘really’ a part of them and we will return to this and analogous problems of differentiating accurate reports of experience from confabulations later in the book. It is possible that these reports are based on beliefs that are not grounded in the patient’s experience of their body at all.

The patient may form a belief, based on some yet to be identified pathology that their body should have one less limb or be paralysed. This belief could then be reported and elaborated into a desire to remove the limb. The proponents of such positions owe us an account of how such a belief is formed, of course. But, they could easily reply that the advocate of the above interpretation owes an account of how patients fail to experience a limb fails as part of their body qua integrated whole. Either account still has considerable work to explain body integrity identity disorder. The issue at hand is whether or not body integrity identity disorder arises out of an unusual experience of the body or out of some other (pathological) belief system. This again turns on whether the reports of these patients are valid measures of how they experience their bodies.

This is not a straight forward problem to solve. One option is to examine the reports of patients suffering body integrity identity disorder. When taken on face value these reports do seem to reflect the experiences the patients have of their bodies. Claims such as “I would have the identity I’ve always seen myself as”; “I feel like an amputee with natural prosthesis”; “I feel myself complete without my leg”; “I felt like I was in the wrong body” (First, 2005, p. 922, emphasis added) clearly appear to be claims that reflect some experience of the body.

Similarly, patients describe odd, but vague, sensations at the demarcation point. One patient who desires paralysis said: “There’s an itch/spot or a mole and it feels that there is something a little different at that point” (case #5 Giummarra et al., 2012). Another subject attempted to explain the feeling saying they know where the demarcation point is via “perception” and not “academically” (case #6 Giummarra et al., 2012).

Should we suppose that these reports are unlikely to reflect the actual experiences of these patients? It might be argued that the very strangeness of these claims is grounds for doubting that they arise from an experience. However, it is common to suppose that even very unusual claims arise from unusual experiences. Take the case of monothematic delusions. The Capgras patient will typically report that a loved one has been replaced by a replica. This is taken to arise from (at least in part) the experience of that loved one as unfamiliar (Young & Leafhead, 1996). Similarly, the patient suffering the delusion of alien control might report that the prime minister is moving his arm. This is taken to arise (at least in part) from an experience of their arm being moved by some other agent (Frith, Blakemore, & Wolpert, 2000; Spence, 2002).

Essentially what we can do is hack our interpretation of reports by attempting a science of experience types

. I will return to this idea in the discussion of confabulation in later chapters. For now, what we can do is record experiences with enough common features for them to be considered a type . This is what we have been doing with BIID and somatoparaphrenia. Once classified, we can ask about what features instances of the type seem to have in common. These common experiences then constitute our first formulation of the phenomena to be explained, i.e. the alteration of the sense of embodiment in those conditions.

Beyond this hack there are observable differences in brain imaging which suggest that stimuli from the rejected body part are processed differently than stimuli from other parts of the body in patients suffering BIID. Magnetoencephalography or MEG records small changes in the magnetic field above the skull due to changes in neuronal firing rates. It is relatively course grained spatially and is only affected by the upper layers of neural tissue (nearest the skull), but it is very fined grained temporally. Normally when the left leg is touched MEG can be used to detect increased activity in a variety of brain areas, including the right superior parietal lobe (SPL). In one study, however, those suffering BIID showed a significantly reduced response in the right SPL for touch to the rejected portion of their left leg compared to an accepted part of the same leg or the equivalent body part in control subjects (McGeoch et al., 2011, p. 1317). This effect was observed only for the right SPL, with patients suffering BIID showing normal activations in other parts of the brain which typically respond to touch to the left leg (McGeoch et al., 2011, p. 1317). This area has also been shown to be reduced in thickness in sufferers of BIID (Hilti et al., 2013).

Hilti and colleagues also found other changes to brain structure, including areas of reduced surface area and increased thickness, yet none of these areas show unusual responses as measured by MEG in McGeoch and colleague’s study. The findings of this study are complicated further by another imaging study, using fMRI. This study showed that activity in the right SPL did not differ between patients and controls (van Dijk et al., 2013, p. 5). However, this discrepancy is explained by van Dijk and colleagues as an artefact of two factors. First, that fMRI does not have the temporal resolution of MEG, and, second, that they used 16 seconds of continuous stimulation, rather than the single touch used by McGeoch and colleagues. Taken together van Dijk and colleagues suggest that the right SPL is merely slow in responding to touch to rejected body parts, but that it does respond (van Dijk et al., 2013, p. 5). This is not the only explanation of the discrepancy available. Notably van Dijk and colleagues included patients experiencing BIID for body parts other than the lower left leg, which could have masked any findings of deactivation in the right SPL. Aside from these specific issues with the imagining findings, there are a variety of well understood limitations on what can reasonably be inferred from contemporary functional and structural brain imaging studies regarding experience and cognitive processing (see, e.g. Coltheart, 2006; Klein, 2009, 2010) and you will see I rely much more heavily on other sources of evidence in this book. None-the-less, McGeoch and colleagues study does seem to suggest that there is some important difference in how stimuli to the rejected body part are processed by those suffering BIID. This in turn, suggests (but does not guarantee) that we’re on the right track in believing that these patients do experience their rejected body part differently than their accepted body parts.

There is other evidence consistent with the hypothesis that such patients fail to experience the body part as a part of the integrated whole that is their body. As discussed above with the rubber hand illusion the anticipation of pain to a body part causes a variety of observable effects on physiology. One of these is an increase in the electrical conductivity of the skin, or “skin conductance response” (SCR) due to sweating. When one anticipates pain one sweats and this can be measured by the SCR. If a patient suffering BIID lacks a sense of embodiment for the limb they desire to be amputated then we can expect a lower SCR for painful stimuli placed near that limb, than when it is placed near another body part. Romano et al. (2015) tested this by holding a needle near the body part which patients desired to be removed. As expected patients showed a lower SCR when the needle was held near the body part they wished removed than near a body part they accepted as their own (Romano et al., 2015, p. 145). This matter is complicated by the fact that patients also showed an increased SCR (relative to control body part) when the needle actually touched the skin of limb the patient desired to have amputated (Romano et al., 2015, p. 145). There are a variety of reasons why this may occur and although the mechanisms are not at all clear, it is possibly due to the fact that stimuli presented to rejected body parts capture attention more strongly than stimuli presented to other body parts. An idea which has some empirical backing from the finding that touch to a rejected body part is processed faster than touch to an accepted body part (Aoyama et al., 2012). It is clear, however, that these patients show an abnormal reaction to pain and the anticipation of pain for limbs which they desire to have removed. This is consistent, but only consistent, with the hypothesis that they lack a sense of embodiment in that limb and fail to integrate it into an experience of their body as a whole.

Ultimately it is an empirical question as to whether any of these reports reflect experiences of the patients. However, it seems that we must be given positive reasons in order to claim that patients’ reports do not arise from their experiences. As no such reasons have been given in the case of body integrity identity disorder, it seems sensible to suppose that such patients really do feel that their limb is not a part of the body.

2.6 Conclusion

Here I’ve attempted to give a description of the feeling of embodiment, which is the target of explanation for the remainder of this book. In its briefest description the feeling of embodiment is the feeling that one is one’s body, or that a body part is a part of one’s self. I’ve suggested that we see clinical alterations of this feeling is asomatognosia and the delusion somatoparaphrenia and that the feeling can be manipulated experimentally using the rubber hand illusion. As these cases involve changes to the feeling of embodiment in particular body parts I also used body integrity identity disorder to argue that there is a feeling of embodiment for the body as an integrated whole. Now to the next task, how to explain the phenomenology of the feeling of embodiment and its clinical and experimental changes?

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© The Author(s) 2019

Glenn CarruthersThe Feeling of Embodimenthttps://doi.org/10.1007/978-3-030-14167-7_3

3. OffLine and On-Line Body Representations

Glenn Carruthers[1]

(1) School of Psychology, Charles Sturt University, Port Macquarie, NSW, Australia

Glenn Carruthers Email: gcarruthers@csu.edu.au

3.1 Introduction

It would come as no surprise to anyone who understands the mind as a computational system (of some form) that what we are looking for to explain the feeling of embodiment and fulfil the function described in Chapter 2 is some sort of representation of the body. But, there is much we need to know about such representations if they are to help us explain the feeling, its breakdowns and experimental alterations. This work begins in this chapter. Here I draw a distinction between two types of body representation, delineated by the representational content of those representations. Both represent the body, but do so in different ways. On-line representations are about the body as it is currently, in contrast offline representations are about the body as it is in general. In the next chapter, we will see that this can be understood as a prototype of the body. Both are needed for the sense of embodiment. By hypothesis we can form on-line representations of any body, yet we typically only experience a sense of embodiment in our own body. How is it that we distinguish our own body as represented on-line

, from other bodies so represented? There are many important sources of information by which this distinction is made, but ultimately, I will argue that it is when an on-line representation of the body matches an offline representation of what that body is usually like that is the sense of embodiment is experienced. It will take the next two chapters to tease out and argue for this hypothesis.

In this chapter, I will make the case that there is a real distinction to be drawn between on-line and offline body representations. This distinction is motivated by a consideration of a tragic disorder called anosognosia for hemiplegia . Sufferers of this disorder are paralysed or severely weakened by a stroke or other brain damage, yet they are unaware of their problem and continue to believe, and sometimes behave as if, their bodies function as they were before the injury. Yet in some contrived circumstances these patients can be made aware of their paralysis or weakness and there is evidence that the new state of their body is represented, but that it does not affect their explicit conscious knowledge of themselves. The distinction between on-line and offline representations, when combined with a hypothesis that various problems caused by stroke can limit access to on-line body representations and the capacity to update offline body representations, is well placed to account for anosognosia for hemiplegia . Such is how I hope to convince you that this is a real and meaningful distinction. I will close with a brief comment on why it seems that offline representations seem to play an important role in the sense of embodiment.

3.2 Body Representation

Let’s begin with Damasio’s suggestion that a representation (or rather a set of representations) of the body provides a natural reference for what happens to oneself as well as a way of understanding objects external to oneself (Damasio, 1994, p. 235). For example, if I asked you where you were on Saturday, you would naturally respond with location of your body. How else could you respond? If I were to drop a brick on you, you could tell the police exactly which part of your body it struck. You also use your body to understand objects external to yourself. For example, when representing the category of cats, you could represent that they tend to move toward (or away from) your body, that they can be patted, et cetera.

For my purposes here, the important claim is that we use the sense of what one’s body is in order to understand ourselves and the world. Damasio suggests that a set of representations of one’s body gives perspective on experience (Damasio, 1994, p. 238). Again, suppose I drop a brick on your foot. You will not undergo a diffuse experience of pain, nor will you experience pain in your head. You will experience pain in your foot. To do this you first need some reference frame for identifying the location of the impact on your body. A representation of your body surface will perform this function. That is, a map of the body surface could serve as a reference frame for impacts on the body.

To do this, Damasio takes it that one can represent one’s body as it has been lately (Damasio, 1994, p. 239). That is, he takes it that the representation of the body is newly constructed moment by moment. This new representation is based partly, though not exclusively (Carruthers, 2008; Tsakiris & Fotopoulou, 2008), on sensory information from the body, such as proprioceptive, kinaesthetic and vestibular information, as well as the senses of touch, heat, cold and pain. As this representation is a newly constructed representation based on current perceptual information it is natural to refer to it as an on-line representation.

I shall argue in coming chapters that a relatively stable off-line representation is also needed to explain the sense of embodiment and its functions. Offline representations of the body are distinguished from on-line representations of the body by their representational content . On-line representations have as their content what the body is like now. That is what movement the body is currently making and the like. In contrast, offline representations have as their content what the body is usually like. For example, instead of representing what movement the body is currently making offline representations represent what kind of movements the body is capable of making. I will have much more to say about how these types of body representation are to be understood later. For now, I wish to convince you that this is a real distinction and put it to work explaining anosognosia for hemiplegia . I will also motivate the hypothesis that an offline body representation (one which represents the body as it is usually) is needed to explain the feeling of embodiment . In the next chapter I will discuss a direct test of the hypothesis that an offline representation is responsible for the sense of embodiment performed by myself and collaborators using the rubber hand illusion . But first, why should you believe in this purported distinction between on-line and offline body representations?

Take the on-line versus offline distinction as a working hypothesis as to two different types of representation of the body either of which could (potentially) feature in an explanation of the feeling of embodiment . I suggest below that anosognosia for hemiplegia can be interpreted in terms of these two kinds of body representation.

3.3 Anosognosia for Hemiplegia

E:

(The examiner put CC’s left hand into the patient’s right, intact, visual field) Can you see it?

P:

(Looking at it) Yes.

E:

(The examiner puts her right index finger in CC’s right visual field) Touch my finger with your right hand (CC does it without hesitation)

E:

Very well. Now, do the same with your left hand . Touch my finger with your left hand .

P:

You are beginning to ask me to [sic] many things!

E:

Please try!

P:

I am trying but I am not able!

E:

Why? Are you weak in that hand ?

P:

No! I am not so silly!

E:

So please try. Are you doing it?

P:

Yes.

E:

Have you already touched my finger?

P:

Not yet… NOW!

E:

Now, please look towards the left (The examiner goes on the left side of the bed and puts her right index finger in front of CC’s into what should be her right visual field but to the left of trunk midline. CC slowly turns her head towards the left). Now, please, look at your left hand (CC looks at her left hand ) and touch my finger with your left hand (CC does not move). Are you doing it? Have you already touched it?

P:

No, but I must succeed.

E:

If, for any reason, you are not able to do it, please tell me why.

P:

I am able… Voila ! (Berti, Ladavas, Stracciari, Giannarelli, & Ossola, 1998, p. 21)

Following stroke (or more occasionally other kinds of brain damage, e.g. due to tumour or seizure Thomas, Giraud, Alchaar, & Chatel, 1998) that has caused paralysis or severe weakness (paresis ) of one or more limbs, many patients fail to report the problem or even explicitly deny that they are paralysed or weak when asked. This lack of insight is known as anosognosia for hemiplegia (or hemiparesis ) (Brock & Merwarth, 1957; Critchley, 1955; Cutting, 1978). Some patients verbally claim that they are not paralysed yet nevertheless act as though they are, in that they never attempt actions with the affected body parts (Vocat, Staub, Stroppini, & Vuilleumier, 2010, p. 3579). However, the disorder is not necessarily limited to difficulties in stating that one is paralysed. Some patients act as if they expect their body to move as they desire (Garbarini et al., 2012). For example , Starkstein, Berthier, Fedoroff, Price, and Robinson (1990) report a patient who repeatedly attempted to walk despite a paralysed left leg. When asked to open a book, Venneri and Shanks ’ patient EN picked the book up with her good right hand by the spine as if to open it with her left (Venneri & Shanks, 2004, p. 233). Marcel, Tegner, and Nimmo-Smith (2004) observation of 64 patients suffering paralysis following stroke confirms that such behaviour is common amongst those suffering anosognosia. This lack of awareness of problems is far more common for left sided paralysis (or weakness ) than right sided paralysis. Although there are cases of anosognosia for right sided paralysis (Welman, 1969), classic studies estimate that around 58% of patients experiencing left sided paralysis (caused by right hemisphere stroke), but only around 6% of those experiencing right sided paralysis (caused by left hemisphere stroke) also suffer from anosognosia or a lack of awareness of their paralysis (Cutting, 1978, p. 551). More recent studies provide lower estimates of prevalence (Vocat et al., 2010), but maintain the strong discrepancy between left and right sided paralysis (Orfei et al., 2007). Most patients come to recognise their paralysis after some days (Vocat et al., 2010), although there are reports of anosognosia persisting for several years (Venneri & Shanks, 2004).

It is common, although not universal, for patients suffering anosognosia for hemiplegia to show other disturbed attitudes toward the target limb and commonly show a deficit in their sense of embodiment in the limb. In their sample Baier and Karnath found that as many as 92% of patients suffering anosognosia for hemiplegia also showed asomatognosia or somatoparaphrenia for the limb (Baier & Karnath, 2008, p. 487). In other words, a majority of those who denied that they were paralysed where unable to attribute their paralysed limb to themselves, instead typically attributing it to others or to no one. Yet this is clearly not a necessary link (as somatoparaphrenia can also occur without anosognosia , Invernizzi et al., 2013), and most of the evidence used below comes from cases of anosognosia for hemiplegia without a loss in the sense of embodiment.

Why might these patients deny their paralysis ? Is it because they still feel that their body can move or is there another reason? Some have proposed that patients suffering from anosognosia deny paralysis in an attempt to protect themselves from the trauma of admitting the problem (see e.g. Orfei et al., 2007 for review). However, such accounts are widely considered to fail to explain anosognosia as they have not explained why the disorder is more common for left than right sided paralysis (Heilman, Barrett, & Adair, 1998, p. 1904), nor why some patients deny paralysis but recognise other severe problems also caused by stroke, such a blindness (Marcel et al., 2004, p. 29; Prigatano, Matthes, Hill, Wolf, & Heiserman, 2011) or even paralysis of another body part (Bisiach, Vallar, Perani, Papagno, & Berti, 1986, p. 473). Additionally, if such accounts are on the right track then patients should acknowledge their paralysis if given a good reason for it, e.g. that it’s an effect of a drug. Yet such prompts do not elicit acknowledgement of paralysis. One patient attempted to explain the ‘fact’ he was not paralysed after such a sham administration by suggesting he was given too low a dose (Cocchini, Beschin, & Della Sala, 2002, p. 3032).

This inability to recognise that one has been paralysed is not simply due to an inability to direct attention to one side of space or of one’s own body. These conditions, known as extra-personal hemispatial neglect and personal hemispatial neglect respectively, do commonly co-occur with anosognosia (Bisiach et al., 1986, p. 474; Marcel et al., 2004, p. 12; Orfei et al., 2007; Vocat et al., 2010, p. 3586) and some cases may be explained by this problem, i.e. some patients may deny that they are paralysed simply because they no longer perceive their paralysed body part (case 2 in Welman, 1969, p. 573 is one possible case). However, both forms of neglect double dissociate from anosognosia, meaning there are cases of neglect without anosognosia (Berti et al., 2005; Bisiach et al., 1986, p. 474; Cutting, 1978, p. 552) and cases of anosognosia without neglect (Adair et al., 1995; Berti et al., 1998, 2005; Bisiach et al., 1986, p. 474; Cutting, 1978, p. 552).

Similarly, the patient’s lack of awareness of being paralysed is not simply due to a lack of sensory input from the paralysed limb. Although there are reported correlations between sensory loss and severity of anosognosia (Vocat et al., 2010, p. 3586), patients suffering from anosognosia have been reported despite no, or only minor, sensory deficits (Bisiach et al., 1986, p. 473; Marcel et al., 2004, p. 30; Starkstein et al., 1990, p. 1380; Vocat et al., 2010, p. 3588). Preston and colleagues report a patient suffering anosognosia for hemiplegia who, despite experiencing visual neglect for his left hemi-field, could detect small changes to limb position and indicate the location of touch on his paralysed arm (Preston, Jenkinson, & Newport, 2010, p. 3444). Furthermore, problems with sensory input from paralysed limbs are no more common for paralysed patients suffering from anosognosia than those who are fully aware of their problem (Feinberg, Roane, Kwan, Schindler, & Haber, 1994, p. 926). Finally, the hypothesis that anosognosia is due to sensory loss fails to explain the asymmetry between left and right sided paralysis (Gilmore, Heilman, Schmidt, Fennell, & Quisling, 1992, p. 926).

Perhaps then the patient suffering from anosognosia lacks insight into their paralysis because they feel that their limb is moving, as in an experience of a supernumerary phantom limb or kinaesthetic hallucination . This proposal too fails to account for anosognosia as not all patients with anosognosia experience such hallucinations , if indeed they are hallucinations —see below (Baier & Karnath, 2008; Cocchini et al., 2002; Feinberg et al., 1994; Feinberg, Roane, & Ali, 2000), and Cutting (1978) reports two patients who experienced supernumerary limbs performing actions but who readily acknowledge that they were paralysed.

Building on their previous work (e.g. Gold, Adair, Jacobs, & Heilman, 1994), Heilman and colleagues (1998) offer an account of anosognosia for hemiplegia on which the underlying deficit in anosognosia is one of the motor control system and not of body representations. Heilman and colleagues assume that one can only recognise a failure to move if one expects to move. When one is suddenly weakened or paralysed by a stroke this change needs to be discovered. They suggest that the patient doesn’t detect their paralysis as they can never form an intention to move the paralysed arm and thus they can never expect to move. This is claimed to be the case even when the subject is explicitly asked to move (Heilman et al., 1998, pp. 1907–1908).

Although this account showed much promise, it is inconsistent with cases in which patients behave as if they expect to move. Below we will see more from patients who would consistently choose to perform bimanual tasks in preference to unimanual tasks. Such behaviour suggests that these patients do expect their paralysed arm to move. As such, it seems they do form intentions to move their paralysed arm (see below and Marcel et al., 2004, p. 33).

Patients themselves describe cases where they attempt to move their paralysed or paretic body parts:

E:

What happened with the stroke? Did you know you had a stroke?

HS:

No, I think I had had it a week before I knew I had had it. When I started my rehab, that’s when I realised what they were saying.

E:

What about your weakness ? Were you weak?

HS:

Not really. Until after I had gotten out of the intensive care and happened to stand up from a chair and tried to sit on the side of the bed and my legs just went from under me.

E:

At that time did you realise why your legs went out from under you?

HS:

No, no I didn’t . (Chatterjee & Mennemeier, 1996, p. 226)

Beyond these cases some patients suffering anosognosia have been shown to contract muscles needed to move their paretic (weakened but not completely paralysed) hands . For example, Cocchini and colleagues’ patient NS contracted muscles in his left arm, which was paretic, when asked to move. He was upset by his failures to move, although this insight was limited and he later claimed not to be paralysed (Cocchini et al., 2002, p. 2032). This patient could form intentions to move, but he could not learn from the failures he detected.

It thus seems that anosognosia for hemiplegia is not motivated denial of a problem, an inability to direct attention to a paralysed limb, a lack of sensory input from a paralysed limb, a hallucination of the limb in action nor an inability to form intentions to act. Having ruled out a lot of good ideas about what is going wrong in anosognosia, in the next section I argue that anosognosia for hemiplegia can be explained by failures to update offline body representations.

3.4 Two Kinds of Body Representation to Account for Knowledge of Limb Functioning

One common way to find out more about how patients suffering from anosognosia for hemiplegia experience their bodies is to confront them with the fact that they are paralysed and attempt to understand their responses. Response to various challenges seem to fall into two broad classes: (A) temporary recognition of paralysis which is quickly forgotten; and (B) confabulation to explain away their failures to move.

Cutting reported a range of responses from patients when asked directly about their being paralysed. These ranged from complete denial to references to the paralysed limb merely being “stiff” or “heavy” (Cutting, 1978, p. 551). It was noted that some patients acknowledged their paralysis at some times, but not others. This gave Cutting the impression that different contexts could elicit different degrees of insight (Cutting, 1978, p. 551). This impression has been borne out by more systematic research.

Asking the patient to perform an action and then drawing their attention to their failure does not typically lead to immediate recognition of paralysis , even temporarily. Most often patients confabulate. They present a semi-plausible story to explain away their failure to move, often using terminology like that noted by Cutting , for example, claiming that they are “just tired” or that they are “just worn out from all the physical therapy” (Feinberg et al., 1994, p. 470). Repeated demonstrations of failure can lead to acknowledgement of paralysis (Marcel et al., 2004; Starkstein et al., 1990), but such admissions are temporary and quickly forgotten.

Given that it will become a problem later in the book it is worth asking now: how do we distinguish between purported accurate reports of the patients experience and their confabulations ? That is, returning to the Real Problem of Consciousness, why think that these reports are reliable measures of what the patients are experiencing. In this instance, the distinction does not seem as problematic as it will become as the kinds of confabulations we see here are provoked by the experimenters questioning (Langdon & Bayne, 2010). The patient’s claim that she didn’t move because of arthritis pain only arises when the experimenter confronts her with her failure to perform a requested action. A most natural interpretation of this is that the “arthritis pain” is confabulated in an attempt to fit into a single, plausible narrative the experience of being able to move and the de facto failure to move. There is much more to say about this later, for now let us return to the nature of the deficit all these patients share.

Damasio attempts to explain anosognosia for hemiplegia with the hypothesis that patients fail to construct accurate on-line representations of their body (Damasio, 1994, p. 64). He notes patients’ “lack of direct update of the state of body and person” (Damasio, 1994, pp. 63–64). For Damasio , such patients seem to fail to form or access any on-line representations of their bodies. There are, however, good reasons to suppose that patients suffering anosognosia for hemiplegia can form on-line representations of their bodies.

The best reason for holding that patients suffering anosognosia for hemiplegia can form on-line representations of their bodies is that they can, under certain conditions, recognise their paralysis . There is a sense in which they appear to be both aware and unaware of their paralysis . Consider, for example, the patient who verbally acknowledged his paralysis, yet who still tried to get out of bed normally (Marcel, 1993). Or the patient who wept when discussing her paralysis, yet who asked for her knitting just minutes later (Marcel, 1993, p. 177). Patients have been known to acknowledge their paralysis after repeated attempts to get them to move the paralysed limb (Cocchini et al., 2002, pp. 2031–2032; Ramachandran, 1995, p. 23). However, not all patients do this, and all revert to denial soon after the acknowledgement

(Karnath, Baier, & Nagele, 2005, p. 7134; Ramachandran, 1995, p. 23).

Under what conditions will patients acknowledge their paralysis ? Patients have been asked to report how well they would perform tasks that required the use of their paralysed limb (Marcel et al., 2004). Those with anosognosia claimed that they would be able to perform the tasks perfectly. However, when they were asked how well the experimenter would perform the task were they in the patient’s condition, they replied that the experimenter could not do it as the task requires the use of both hands (Marcel, 1993, p. 177; Marcel et al., 2004, p. 33). This suggests a difference in awareness of paralysis depending on the perspective the patient takes to the disorder.

It was also found that how examiners ask question could affect the responses patients give. If the examiner asks ‘does your arm ever not do what you want it to?’ in a confiding voice patients were more likely to respond affirmatively than if the question was asked in a neutral tone (Marcel, 1993, p. 177; Marcel et al., 2004, p. 33).

In another test patients were given a choice to perform two tasks for a reward (Ramachandran, 1995). The tasks were either a unimanual tasks , such as threading a screw, or bimanual, such as tying a knot. Those who successfully performed the bimanual task received a greater reward than those who performed the unimanual task. Those suffering hemiplegia without anosognosia always chose the unimanual task —despite the lesser reward. However, those with anosognosia for their hemiplegia nearly always chose the bimanual task, as healthy controls did. Initially it seemed that those with anosognosia were unable to learn that they were paralysed from attempting to perform bimanual tasks (Ramachandran, 1995, p. 31) or other actions involving the paralysed or paretic hand . Further studies have suggested that this is not quite true. Some patients suffering anosognosia can learn from such failures (e.g. 7/15 do in Adair et al., 1997; and 5/7 do for Cocchini, Beschin, Fotopoulou, & Della Sala, 2010, p. 1493). However , this learning does not have long term effects on their understanding of their bodies. As soon as twenty minutes after an unsuccessful attempt to perform a bimanual task , patients forget their failure (Marcel et al., 2004, p. 33). It seems that at sometimes the patient suffering from anosognosia can represent what their body is like currently, but that this is not always the case.

Further evidence that this representation is formed, but that access to it is impaired, comes from Fotopoulou, Pernigo, Maeda, Rudd, & Kopelman (2010). They examined 7 patients suffering complete left arm paralysis and anosognosia and 7 suffering the same paralysis but who acknowledged the problem (Fotopoulou et al., 2010, p. 3566). One of the patients suffering anosognosia also suffered from somatoparaphrenia (Fotopoulou et al., 2010, p. 3566). The two groups completed a version of the Haylings sentence completion task . This task is designed to measure patients’ capacity to inhibit their natural responses (Burgess & Shallice, 1996). Patients are read a series of sentences aloud with the final word missing, for example; “The dough was put in the hot _____.” The task is to “complete” the sentence with a word that makes no sense, for example, “goat”. Whereas an intuitive finish to the sentence, for example “oven”, is an error. Fotopoulou and colleagues modified the task to use emotionally neutral sentences about cars, negative sentences about physical assault, and “deficit related” sentences about brain damage and paralysis (Fotopoulou et al., 2010, p. 3567). Fotopoulou and colleagues also asked patients to rate, explicitly, how relevant each sentence was to their current situation. This resulted in three measures of task performance (1) Explicit rating of the self-relatedness of sentences; (2) The number of errors made in “completing” the sentence; and (3) The patient’s response time in coming up with a word (Fotopoulou et al., 2010, p. 3569).

As one would expect given the nature of anosognosia for hemiplegia , patients suffering from anosognosia rated the “deficit related” sentences as less self-relevant than paralysed patients not suffering anosognosia (Fotopoulou et al., 2010, p. 3569). There was no difference between the groups for negative and neutral sentences. Importantly, patients suffering anosognosia were slower in responding to deficit related sentences than neutral sentences. In contrast, they responded to negative sentences at the same speed as neutral sentences (Fotopoulou et al., 2010, p. 3570). However, patients suffering from anosognosia did not make more errors in completing sentences than control patients (Fotopoulou et al., 2010, p. 3570). This shows that patients suffering anosognosia could inhibit natural responses to completing sentences, but they were slower for sentences about brain damage and paralysis . Similarly, patients suffering anosognosia have been shown to take longer to respond to neutral stimuli when primed by words related to paralysis (Nardone, Ward, Fotopoulou, & Turnbull, 2008).

Fotopoulou and colleagues interpret this and similar findings as suggesting that some representation of the patient’s paralysis exists and interferes with processing of information about paralysis . Although there are other reasons why this interference effect may occur, this pattern of results is predicted by the hypothesis that patients suffering from anosognosia do form an on-line representation of the current state of their body, qua paralysed, but that this representation cannot be accessed under most conditions. This result converges nicely with other evidence considered in this section.

One way for most of those suffering anosognosia to gain access to the current state of their body is via vestibular stimulation with cold water (i.e. squirting cold water in the patient’s ear). It is not clear how this process works, however, it is clear that it allows patients to have access to the current state of their body (Ramachandran, 1995, pp. 34–35). Like learning from failure to perform bimanual tasks , vestibular stimulation only has a short-term effect on the patient’s insight. A few hours after stimulation the patient again claims not to be paralysed.

Finally, it is common (although not universal) for anosognosia for hemiplegia to remit a few weeks after onset (Vallar & Ronchi, 2009, see Tables 1 and 2). At this time patients come to acknowledge their paralysis are able to report previously being unaware of their paralysis or paresis and some are able to correctly identify when their paralysis began (Chatterjee & Mennemeier, 1996). There are also preliminary studies which suggest that remission can be triggered by providing patients with an alternative perspective on their bodies using video replay (Besharati, Kopelman, Avesani, Moro, & Fotopoulou, 2015; Fotopoulou, Rudd, Holmes, & Kopelman, 2009). This method shows much promise for patients in that the remission seems longer lasting than that caused by other techniques. It seems that due to vestibular stimulation , or recovering after the brain damage, patients suffering from anosognosia can come to represent the current state of their body.

As such those suffering from anosognosia do seem to form on-line representations of their body, yet they are unable to access these representations most of the time. When the patient suffering anosognosia is unable to access their on-line representations of the body they still seem to have access to another representation of the body, one that represents the body as able to move. I suggest that the best way to understand anosognosia for hemiplegia is in terms of two types of body representations that are accessed under different conditions. The first type is the on-line representation of the body. This is the type of representation of the body that the patient accesses when they acknowledge that they are currently paralysed. This is accessed when the patient is asked to put another in their condition, when asked about their paralysis in a certain tone of voice, when confronted with failure at bimanual tasks and when undergoing vestibular stimulation . As we have seen, such representations can interfere with semantic processing even when they are not consciously accessed. The second type of representation of the body I call ‘offline’ representations. This is the type of representation that patient accesses under all other conditions.

How does this help us understand anosognosia? Suppose I were to ask you if you can move. To answer you wouldn’t need to test yourself to find out (Marcel et al., 2004), you might because it’s a strange question, but you wouldn’t need to. Instead, you could answer based on a generic understanding of your body. That is, based on a stable offline representation of what your body is usually like. The patient suffering anosognosia for hemiplegia uses the same method. Only their offline representation is now out of date. For some reason, new information from the body has not updated it since the patient was paralysed. Suppose one of the above methods (e.g. vestibular stimulation ) is used to give the patient access to the current state of their body. They can use this representation to judge that they are, in fact, paralysed. However, this representation fails to update the offline representation of the body. As such when they stop paying attention to the on-line representation they will lose the representation of themselves as paralysed. After a time, the patient will again deny that they are paralysed, as they will answer all such questions based on the offline representation of their body, which is not being updated. As was mentioned above, there is reason to be optimistic that more long-term learning can be supported using video replay techniques (Besharati et al., 2015).

Yet it is not clear that the offline body representation is updated even after patients come to acknowledge that they are paralysed. Patients have been known to report that they still feel as if they can move normally even though they know they cannot:

E:

What was the consequence of the stroke?

HS:

The left hand here is dead and the left leg was pretty much.

HS (later):

I still feel as if when I am in a room and I have to get up and go walking . . . I just feel like I should be able to.

E:

You have a belief that you could actually do that?

HS:

I do not have a belief, just the exact opposite. I just have the feeling that sometimes I feel like I can get up and do something and I have to tell myself ‘no, I can’t ’’ (Chatterjee & Mennemeier, 1996, p. 227).

E:

How much strength do you have on your left side at this point?

EM:

Below normal. I’d say 40% or less.

E (later):

Can you raise both arms? (Only lifts the right.) Can you raise the left one?

EM:

It feels like it’s rising, but, it’s not.

E:

You thought you had about 40% strength in your left arm. Do you think that’s accurate?

EM:

No, less than 40%.

E:

What percent would you rate it at the moment?

EM:

Right at the moment only 10%. Less than 10% . (Chatterjee & Mennemeier, 1996, p. 229)

Similarly, after treatment using video feedback, Besharati and colleagues’ patient was asked if she could get out of bed without help, to which she replied “No I can’t, yet I think I can ” (Besharati et al., 2015, p. 334).

Reports such as this, should they turn out to accurately describe the patients experience, suggest that when insight does come it comes from a form of long-term semantic memory and not from an updating of an offline body representation. Although it must be cautioned that even when patients acknowledge that they are paralysed, they don’t always seem to grasp the full consequences of this (Chatterjee & Mennemeier, 1996, p. 231). Which leaves open the possibility that they were merely telling doctors what they wanted to hear when acknowledging their paralysis . None-the-less if their apparent insight is genuine, there are several sources of information available to patients from which they could build knowledge that they are paralysed, such as being in a hospital and being told they are paralysed, de facto failures to move and the like. It is possible then that patients for whom anosognosia has remitted know they are paralysed because they declaratively remember that they are and not because they’re experience of their body has changed.

3.5 Pluralism

About Anosognosia for Hemiplegia

Many contemporary theorists are pluralists in their attempts to understand anosognosia, in that they suppose there are multiple causes of anosognosia. Such accounts start from some of the dissociations noted above, that anosognosia dissociates from hemispatial neglect , general memory problems and kinaesthetic hallucinations . To this we might also add that it appears to dissociate from problems forming intentions to act. Yet these dissociations are a minority of cases and whilst they are certainly evidence that one of these factors cannot be a sufficient cause of anosognosia in every patient, they do not rule out the possibility that several factors, in different combinations, do explain anosognosia. For example, Vallar and Ronchi say:

In the light of all these dissociations, the argument may be put forward that, in different patients, the combination of different impairments (e.g., touch or proprioceptive sensory deficits ; higher level cognitive disorders, such as confusion, reduced general intelligence, or defective short-term, working, or episodic long-term memory), may bring about unawareness of disease. According to such a view the deficit is not one of specific function monitoring, but a more generic disorder, whereby single or multiple impairments of other lower (sensory) or higher level (orientation, intelligence, memory) systems may bring about unawareness , with a variety of possible pathological mechanisms . (Vallar & Ronchi, 2006, p. 250)

Orfei and colleagues go a step further, suggesting that anosognosia for hemiplegia may not be a single disorder:

By examining and comparing contributions about anosognosia for hemiplegia in stroke patients, the description of a very complex and multifaceted matter emerges, in which different manifestations may be present to various degrees and prevent the development of a single diagnostic entity . (Orfei et al., 2007, p. 3086)

In arguing that anosognosia is to be understood as a failure to update the offline body representation am I swimming against the river orthodox? The account offered here is consistent with a pluralism about the causes of anosognosia for hemiplegia . Although it seems likely that anosognosia for hemiplegia may have many causes, it also seems likely that these causes all interfere with a common mechanism, namely the updating of offline body representations. For example, the case of NS can be understood in this way. This patient had an unusually long run of anosognosia, probably due to persistent anterograde amnesia following the accident which also caused his paresis , and which prevented him from updating his offline body representation. Consistent with pluralism not all cases of persistent anosognosia for hemiplegia are likely to be explainable in terms of global memory deficits (Venneri & Shanks, 2004). Indeed , we may speculate that the patients which inspired Heilman and colleagues’ account did fail to detect failures to move because they couldn’t try to move and without such failures they couldn’t update their offline body representations. Individual differences in the recovery of the mechanism for updating the offline representation is one place to look for explanations of the variation in time to remission for anosognosia (Cocchini et al., 2002). But, however this turns out, it seems likely that there are multiple possible causes for a failure to update an offline body representation to represent that one is paralysed or paretic, and so, in a sense, multiple possible causes of anosognosia for hemiplegia . Working out which of the ways in which we can imagine a failure to update an offline body representation actually occurs in patients is a hugely important question, but it is a question for a different book. What matters for the argument I am concerned with here is the offline body representation itself and its relationship to the sense of embodiment.

3.6 A Gesture at the Sense of Embodiment

So far in this chapter, I have argued for the existence of two kinds of body representation. The first of these is an on-line representation of what the body is currently like. This is an explicit conscious representation. The second type of body representation is an offline representation; one that is not directly ‘plugged into’ the body. The offline representation represents what the body is usually like. It represents that one has two arms, that one has a weak left ankle and the like, not, for example, exactly where one’s limbs are currently. This can be a tacit representation (stored in memory) or an explicit conscious representation.

I claim that it is this relatively stable offline representation of the body that underlies the sense of embodiment. As I noted in the first section , Damasio (1994) suggests that it is a series of on-line representations of the body that explain these senses. This is not the case. Above we saw that patients suffering anosognosia for hemiplegia misrepresent their bodies because they cannot update their offline body representation and have limited access to their on-line body representations. However, these patients don’t necessarily claim to feel disembodied. It is true that most patients suffering from anosognosia for hemiplegia also suffer from delusions of somatoparaphrenia , but this is not universal. We need an account of patients suffering anosognosia who don’t claim that they are not within their body, but that do make incorrect judgements about their bodies. Bad access to on-line body representations does not cause one to feel disembodied. As such on-line body representations alone cannot underlie the sense of embodiment. Offline body representations are also needed to account for the feeling of embodiment . I discuss how in the next chapter.

3.7 Conclusion

In this chapter, I have begun to motivate the hypothesis that an integrated, offline body representation is needed to explain the sense of embodiment. I have presented an interpretation of anosognosia for hemiplegia that supports this distinction, whilst leaving an important role for offline body representations in explaining the sense of embodiment. In the next chapter I examine how this account can be extended and tested with a consideration of the rubber hand illusion and somatoparaphrenia .

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© The Author(s) 2019

Glenn CarruthersThe Feeling of Embodimenthttps://doi.org/10.1007/978-3-030-14167-7_4

4. Explaining the Feeling of Embodiment: The Feeling of Embodiment Occurs When an On-Line Body Representation Is Matched to an OffLine Prototype

Glenn Carruthers[1]

(1) School of Psychology, Charles Sturt University, Port Macquarie, NSW, Australia

Glenn Carruthers Email: gcarruthers@csu.edu.au

This chapter makes use of material previously published as: Carruthers, G. (2013).

4.1 Introduction

So far, in attempting to explain the feeling of embodiment I have used pathologies of body experience to motivate the hypothesis that the feeling is underlain by an offline body representation. Now it is time to get specific. In this chapter I aim to explain a well-defined controllable experience, the feeling of embodiment during the rubber hand illusion. We will see here that the best version of this hypothesis holds not that offline representations are causally elicited and that this explains the feeling of embodiment. Rather it is on-line body representations which sit in appropriate similarity relationships to offline body representations which carry this phenomenology. But, it is only in virtue of being in the right relationship to the offline representation that they are able to do so. In order for this to make any sense both types of body representation and the process of matching them must be understood in terms of conceptual or quality spaces.

I argue that the sense of embodiment arises when an on-line representation of the candidate body part is represented as matching an offline prototype representation of what one’s body is usually like. This explanation is both causal and constitutive. It is causal in that it provides an account of the processes leading to the sense of embodiment being elicited. It is constitutive in that in provides a description of the mental representation which constitutes the sense of embodiment. I begin with a description of the rubber hand illusion, with a focus on the nature of the phenomenal experience of being embodied in the rubber hand, which is our explanatory target. I will present a model of the cognitive mechanism underlying the illusion. A central distinguishing feature of this model is the offline body representation. I propose that the offline representation is a point (or set of points ) in a quality space (‘body space ’) which corresponds to a prototype arrangement of one’s own body. If so, then we have a powerful explanation of the rubber hand illusion. Whether or not a particular on-line representation matches the offline prototype is determined by the distance between the prototype and a point corresponding to the on-line representation in body space . Only the on-line representation need be occurrent, but it has part of its content that it is a representation of one’s own body only in virtue of its relationship to the offline prototype. In this way it can carry the feeling of embodiment.

4.2 A Model of the Sense of Embodiment in the RHI

We met the phenomenology of the rubber hand illusion earlier on, now it’s time to explain how the feeling of embodiment is changed in the illusion. The rubber hand illusion (RHI) is the experience of an artificial body part as being the real body part, most commonly a hand. That is, it involves the feeling of embodiment in artificial body part. It is this instance of the feeling of embodiment which I am aiming to explain in this chapter, for if we can explain this experience in this instance, hopefully we can explain it in others too. We will see that there is hope of extending this account to losses of the sense of embodiment in the delusion of somatoparaphrenia.

Here I propose that the sense of embodiment in a rubber hand is elicited by a process of matching two types of body representations, on-line and offline body representations. But, as we will see this is not only a causal explanation, but also a constitutive one. Ultimately the feeling of embodiment is hypothesised to be identical with the content of any on-line body representation falling sufficiently close to an offline prototype. We’re some way off making sense of that, so let’s start at the beginning.

First some reminders about the tools we are using. Offline body representations have as their content one’s body (especially its spatial features) as it is usually. On-line representations, in contrast, represent the current state of the body. This distinction was originally proposed to explain why patients suffering from anosognosia for hemiplegia are, at times, able to recognise their paralysis (Carruthers, 2008b). Offline body representations are thought to be closely related to the sense of embodiment (Carruthers, 2008b, 2009, but see also Carruthers, 2008a; De Preester & Tsakiris, 2009; Tsakiris, 2010; Tsakiris & Fotopoulou, 2008). Some evidence of this relationship comes from the RHI itself. Ehrsson, Holmes, and Passingham (2005) report that during the tactile RHI (seeming to touch one’s own hand when touching a rubber hand) subjects disagreed with the statements “I felt as if I had more than one right hand” and “I felt as if my right hand were larger than normal” (Ehrsson et al., 2005, p. 10567). These suggest that the illusion does not easily allow for violations of the parts of the body (one right hand is much more likely than two) or of the size of those parts, which typically change slowly or not at all. This is expected if offline body representations underlie the sense of embodiment, as offline body representations ought to represent the body as having just one hand on each side and as of relatively fixed dimensions, since this is how the body is typically arranged.

Let’s have a look at the model in general terms, before focusing in more detail on the nature of offline and on-line body representations and on what information is used to determine a match.

4.2.1 The Causal Sequence Leading to the Illusion and Represented Location of the Real Hand

According to the model presented here, the first stage of the rubber hand illusion involves the integration of sensory information to form an on-line representation of a perceived body, or an object which may be a part of the body. This process, and I’ll hang a lantern on this, I will leave largely under-defined here. Sensory information can contribute to the formation of this representation if it is about something which is body-shaped, or if it is about an event already represented as occurring to a body. I take it we have on-line representations of any body which we perceive, be it our own or someone else’s. These may or may not fall into the conceptual/quality space around an offline prototype. This allows for the cross-modal integration of sensory events in non-body-like objects, such as synchronous touch on one’s own hand and a table top or white box (as in Hohwy & Paton, 2010), but not a sense of embodiment in such objects. Similarly it allows for the cross-modal integration of synchronous touch on one’s real hand and a model hand. By this I mean that these two events are represented as though they are a single event. This, we shall see, is necessary but not sufficient for the RHI to be elicited.

Once an on-line representation of a body is formed, it can be compared to the stored offline representation of what one’s body is usually like. This comparison determines whether or not the body currently being represented on-line is taken to be the same body as represented by the offline prototype. I suggest below that this process be understood in terms of a conceptual or quality space: whether or not the two representations represent the same body is determined by how close[1] the on-line representation falls to the offline prototype in quality space. The distance between the on-line representation and the offline prototype determines the represented similarity between the hand represented on-line and the hand represented offline. How close is close enough remains an empirical question. For now, let me list some criteria, which can be altered in experimental set ups, and which may be influencing this matching [2]:

Synchrony of touch:

Is the seen and felt touch (the standard illusion and the passive movement version, as in Tsakiris, Prabhu, & Haggard, 2006), or double touch (tactile version, as in Ehrsson et al., 2005) synchronous?

Proprioception and touch:

is any information about the body received proprioceptively or by touch?[3]

Arrangement:

is the body arranged, from one’s own point of view, in a way that it could be one’s own? This criterion will naturally exclude other people’s bodies (in all but the most enjoyable circumstances) from being taken as one’s own.

Shape:

is the body in the on-line representation shaped as one’s body as represented in the offline prototype is shaped?

Action:

does the body represented in the on-line representation act as predicted by one’s motor system?

If the body as represented on-line is represented as matching the body as represented offline, then the sense of embodiment is elicited for the body represented by the on-line representation. I say elicited, but ultimately I hypothesise that the feeling of embodiment is carried by the on-line representations in virtue of the fact that it represents one’s own body. It has this content in virtue of bearing the right similarity relationship to the offline prototype. To understand how this works we will need to look more closely at conceptual/quality space representations.

If the body as represented on-line is represented as matching the body as represented offline, then the sense of embodiment is elicited for the body represented by the on-line representation. This can be summarised as in Fig. 4.1. Figure 4.1 amounts to an explanation schema, by which each instance of the rubber hand illusion could be explained by inserting particular representations.

Fig. 4.1

The causal chain (inside the cognitive system) leading to the sense of embodiment. Sensory information classed as related to some body or not is unified into an on-line body representation of the perceived body. If that body is represented as the same body represented by the offline body representation then the sense of embodiment is elicited. Such a match involves the on-line body representation falling close to the offline prototype (see below). Factors influencing whether or not the on-line representation matches the offline representation are whether or not any proprioceptive or touch information comes from the body represented on-line, whether the body represented on-line is shaped and arranged as one’s body could be and whether or not the body represented on-line moves as predicted. The RHI occurs when the rubber hand is mistaken for the real hand as represented in the offline model. This is due to an illusory experience of touch coming from a hand which is shaped and arranged in a way which is plausible for one’s own body as represented offline, and in some conditions that the model hand moves as predicted. In this diagram particular types of mental representation are named in ellipses and are identified by their content. Arrows represent computations over those representations. Thus, the syntax of this diagram departs significantly from the standard form laid out by Coltheart (2002) (Reproduced with permission from Imprint Academic)

The rubber hand illusion commonly co-occurs with changes in the represented location of the real hand for perception and action. Some use this change, termed “proprioceptive drift” to measure the presence of the illusion. Here I argue that the data suggests that, whilst commonly co-occurring with the illusion, drift is partially independent of the illusion. I make sense of this by proposing a partial overlap in the causes of drift and the sense of embodiment.

First consider a case of proprioceptive drift that occurs without an illusion of embodiment and hence no rubber hand illusion. We will see that creating a mismatch between the seen and felt location of a subject’s hand causes changes in the represented location of the hand without causing an illusion of embodiment in the image one sees. To create a mismatch between the seen location and the felt location of the hand, Holmes, Snijders, and Spence (2006) had subjects sit at a table with their left hand behind a mirror. The experimenter positioned the subject’s left index finger on one of four markers at various distances from the reflective surface of the mirror. The subject’s task was a simple point to point movement, moving their left index finger to a second mark. Their only feedback on this task was from the experimenter who gave both verbal feedback and moved the subject’s left index finger to the target, although there was a second target mark to the right of the mirror such that its reflection seemed to spatially overlap with the target on the left. Subjects practiced until they were consistently good at reaching the target (Holmes et al., 2006, p. 687). Once they were well practiced, subjects were shown their own right hand, a rubber hand in a congruent position with their left hand, a rubber hand upside down relative to their left hand, or a wooden block reflected in the mirror (when observing the rubber hand or block, the subject’s right hand was placed next to the object behind a mask). This object was positioned such that the reflection of the left index finger or left corner of the block appeared to be displaced by 0.025 m or 0.075 m to the left or right of the real location of the left index finger. Subjects looked at the reflected object (right hand, rubber hand or block) for 12 s and then to the reflection of the target when they made the movement (Holmes et al., 2006, p. 688). During the experiment nothing was done which could elicit the RHI, i.e. there was no synchronous stroking or action, and more importantly subjects did not report feeling as though they were looking at their left hand when given the RHI questionnaire (Holmes et al., 2006, p. 692).

Holmes and colleagues measured the distance to the left or right of the left index finger at the endpoint of the reaching action from the target they practiced reaching toward. They found that subjects ended their reaches a greater distance from the target when they saw their own right hand or a rubber hand reflected in the mirror than when they saw a wooden block (Holmes et al., 2006, p. 689). Similarly, the upside-down rubber hand resulted in significantly smaller errors (Holmes et al., 2006, p. 692). The errors were always in the same direction from the target (left or right) as the left hand was displaced from the reflection, i.e. if the left index finger was to the left of the apparent location of the reflection of a finger then subjects finished their actions to the left of the target. This suggests that when given visual cues to create a representation of the location of the hand to the left (or right) of its actual location, subjects act as though their hand is closer to the illusory (visually represented) location then it is. Importantly this is the case even though subjects were not experiencing the RHI. As such, in this case it is clear that misleading visual feedback alters the represented location of the hand for action representation of the hand.

What we see in this study is visual perception ‘capturing’ proprioception in generating a representation of hand location for action. This occurs only when the seen object is hand-like, and not when it is a wooden block or a hand arranged in an implausible fashion. Importantly the represented location of the hand (at least for action) is affected by vision even when the RHI is not present. That this only occurs for hand-like objects suggests that a representation of the body, such as an on-line representation, is necessary for the shift in represented location to occur. This suggests a dissociation between mere visual capture and the RHI, and (importantly for my purposes here) between the represented location of the hand and the sense of embodiment.

I propose that drift be understood as due to the formation of an erroneous on-line representation of the body, leading to a misrepresentation of the location of the hand for action. The erroneous on-line representation may or may not then be matched to an offline representation of the body. In the case of the RHI it is so matched, while in Holmes and colleagues’ study it is not. To account for this I propose a split in the causal pathways leading to drift, on the one hand, and to the sense of embodiment following the formation of an on-line representation, on the other hand, as depicted in Fig. 4.2. We also see here an explanation for why the illusion and drift commonly co-occur, namely they share a partial common cause in the formation of an erroneous on-line representation.

Fig. 4.2

The separation of the causal chain leading to drift from that leading to the illusion. Drift and the illusion share common causes up to the formation of the on-line body representation, which explains why they commonly co-occur (Reproduced with permission from Imprint Academic)

This hypothesis can explain further evidence that drift is not a necessary feature of the illusion. Hohwy and Paton (2010) describe a version of the RHI in which no drift occurs and furthermore, in which no drift would be expected due to the artificial hand appearing to be in the same space as the real hand. They showed a skin temperature drop for a real hand when the illusion was induced for a video image of a hand which appeared in the same space as the real hand. This suggests that the RHI can be elicited for an artificial hand that appears to be in the same space as the real hand (Hohwy & Paton, 2010, p. 4). The very least we can say from this is that not all versions of the RHI can be measured by proprioceptive drift. More strongly than this, I argue below that there is evidence that proprioceptive drift varies independently of the illusion in cases where the artificial and real hand are separated in space . Any explanation of the RHI must at least allow for this possibility.

The subjective vividness of the rubber hand illusion can be varied independently of drift. We can see this dissociation in a study from Ijsselsteijn, de Kort, and Haans (2006). They attempted to elicit the RHI using three variations of the set up introduced by Botvinick and Cohen. First, they used the standard set up where the subject watched a rubber hand being stroked in synchrony with their real hand, which was out of sight behind a screen. Second, the rubber hand was replaced by a live projected image of the rubber hand being stroked in synchrony with the real hand. This they called the ‘virtual reality’ condition. Finally, subjects saw a projected image of the rubber hand, and the experimenter then stroked the image in synchrony with then real hand. This they called the ‘mixed reality’ condition (Ijsselsteijn et al., 2006, p. 458).

Ijsselsteijn and colleagues used Botvinick and Cohen’s questionnaire to measure the subjective strength of the illusion. For question 1 (“It seemed as if I were feeling the touch in the location where I saw the hand”) subjects gave the highest scores in the traditional set up and lower scores for the two new set ups. This indicates that the feeling of the location of touch as being in the rubber hand was strongest for the traditional condition. The scores given in the two new set ups did not differ for this question. However, they did differ for question 2 (“It seemed as if the touch I felt was caused by the paintbrush touching the rubber hand/image”) and 3 (“I felt as if the rubber hand were my hand”) (Ijsselsteijn et al., 2006, p. 461). For these questions the traditional set up resulted in the highest scores and mixed reality the lowest. The virtual reality condition lay in the middle and all differences were significant (Ijsselsteijn et al., 2006, p. 461). These patterns of answers suggest that the vividness of the illusion can be varied by using these different conditions.

Ijsselsteijn and colleagues measured proprioceptive drift as well as giving the questionnaires. Both the mixed reality and virtual reality conditions resulted in less drift than the traditional set up. However, drift did not vary between the mixed reality and virtual reality conditions (Ijsselsteijn et al., 2006, pp. 461–462). That is, the vividness of the illusion as reported by questionnaire responses varies in this case when drift does not. This suggests that the vividness of the illusion can be altered by changing conditions without altering proprioceptive drift. To be precise, the extent to which subjects felt as though the hand they saw was their own was significantly affected by whether both the hand and stroking were projected in front of the subject (in the virtual reality condition) or whether just the hand was projected and the image itself stroked (in the mixed reality condition). However, this variation did not affect proprioceptive drift. Thus, the vividness of the RHI is not always correlated with the magnitude of drift.

Along similar lines Pavani and Zampini (2007) suggest that making the image of the hand smaller than the real hand eliminates proprioceptive drift, but does not eliminate the experience of the illusion as reported by questionnaire answers.

Further the magnitude of proprioceptive drift can be affected without affecting the vividness of the illusion. Kammers et al. (2008) investigated the rubber hand illusion following an induced reduction in excitability (i.e. a reduced chance of firing) of the inferior posterior parietal lobule (IPL) using repetitive transcranial magnetic stimulation (rTMS). Subjects in this study first underwent either real or sham TMS over the IPL, after which a second experimenter (who was blind to the kind of stimulus) attempted to elicit the RHI with synchronous stroking of a rubber hand and the subject’s real hand (Kammers et al., 2008, pp. 1312–1313). After induction of the illusion or control stimulation, subjects were given a questionnaire and were also asked to perceptually judge the location of their stimulated finger. It was found that proprioceptive drift was significantly smaller in those subjects who underwent real rTMS (Kammers et al., 2008, p. 1316). However, the strength of the illusion reported by the questionnaire did not differ by which stimulation subjects received (Kammers et al., 2008, p. 1316). In other words, the strength of the illusion as measured by self-report was not affected by rTMS over the IPL. As such we can see that the magnitude of proprioceptive drift can vary independently of the experience of the illusion.

So far, I have described the causal chain within the cognitive system which leads to the RHI and how this splits from the chain leading to represented location of the hand for action. Next, I examine in terms of a conceptual space the key process of matching on-line and offline body representations.

4.3 Conceptual/Quality Space Representations

The hypothesis here is that the RHI occurs when the observed rubber hand is mistaken for the real hand as represented in an offline body model. I propose, however, that the offline body representation is not a particular occurrent representation. Rather the offline body representation is a point defining a prototype body in a quality or conceptual space into which an occurrent on-line representation of a body may or may not fall. If the on-line representation represents one’s own body it falls within this space , if it does not represent one’s own body it does not fall in this region.

Conceptual or quality spaces are a way to represent particulars which fall under a concept or class. Each point in the space represents a possible particular. Such spaces are first up abstract objects (Gärdenfors, 2000, p. 31). However, they are in principle implementable in artificial neural networks (Gärdenfors, 2000, p. 7) where each activation of the network (or a layer of the network) corresponds to a point in conceptual space (O’Brien & Opie, 2000). The below description of conceptual spaces is largely derived from the account given by Gärdenfors (2000). It is worth noting both that at times Gärdenfors himself is open to a form of instrumentalism regarding conceptual spaces, in that he remains neutral as to their ontological status (Gärdenfors, 2000, p. 31). To many this will be a point against their use in explanations. However, there is no necessity to follow Gärdenfors’ instrumentalism, and indeed there are some who are clearly realist about such spaces, e.g. Churchland (1995) and O’Brien and Opie (2000) discuss the implementation of such spaces in the activation spaces of artificial neural networks. Gärdenfors’ himself is open to a similar form of realism (see e.g. Gärdenfors 2000, Chapter 7 espc. pp. 244–245). Although I have relied heavily on Gärdenfors’ description of conceptual spaces this is not the only available account of conceptual/quality spaces, and such spaces have been productively applied to other experiences such as colours (Hardin, 1985), sounds, tastes, and smells (see Clark, 1993 for review). I do not wish to enter into these issues in detail here. I merely wish to avoid the appearance of endorsing any form of instrumentalism.

Conceptual spaces are composed of the space defined by particular quality dimensions (Gärdenfors, 2000, p. 5). A quality dimension is a line where each point on the line represents the value of a quality of a particular. A quality here is defined as a way in which particulars can be judged to be similar or different to one another (Gärdenfors, 2000, p. 6). For example, the quality dimensions defining colour space are hue, saturation, and brightness (Gärdenfors, 2000, pp. 9–10; Hardin, 1985). Each particular colour can be judged to be more or less similar to all other colours on these dimensions. The concept of colour is represented by the space defined by these three dimensions. The space can also partitioned into smaller regions (Gärdenfors, 2000, p. 60), with each region corresponding to a concept subordinate to the primary concept. For example, the concepts of red or green are represented by regions within colour space. [4]

The perceived similarity between two objects corresponds to the distance between the two points representing those objects in conceptual space (Gärdenfors, 2000, pp. 8, 45). How distance between points is to be measured, or the metric of the space, varies between spaces (see Gärdenfors, 2000, pp. 17–21 for an introduction). The structure of the relations between each point may also determine the representational content of each point and is crucial for understanding how such spaces can be implemented in artificial neural networks (O’Brien & Opie, 2000). How the distance between points is determined depends on the nature of the space defined by the quality dimensions (Gärdenfors, 2000, pp. 18–19): even if the dimensions define a Euclidean or Cartesian space, the relationship between similarity and distance need not be linear (it may be, e.g. exponential) (Gärdenfors, 2000, p. 21). So long as the relationship is definable and consistent the representational powers of the conceptual space remain intact.

The above description of conceptual spaces is taken from the account given by Gärdenfors (2000). Conceptual spaces described here are intended to provide tools for analysing how we represent certain concrete objects and how we performed computations using those representations. However, to see their use in describing experiences we need only add the assumption that the objects in question are experienced by the subject. A quality space is a description of the conscious representations of those objects, i.e. of the subject’s experience of those objects. A subset of conceptual spaces then, those corresponding to our conscious representations of concrete objects, are also quality spaces.

Quality spaces provide a description of experiences in terms of how those experiences can be distinguished from one another (Clark, 1993, p. 197). For a quality space for hands each point in the space will represent the experience of a hand and the dimensions of the space will correspond to the ways in which experiences of hands can differ. Below I describe an experiment in which we have attempted to approximate this space using the space describing subject’s experiences of a small set of photographic depictions of hands. There are some limitations from this approximation which we needed to cop to make this, first of its type, experiment work. For example, it is possible there is some information that can be used to distinguish real hands that is lost in 2 dimensional photographs, no matter how good the photograph is. However, as things stand, we have no reason to think that the space describing experiences of hands will differ systematically and radically from a space describing experiences of images of hands. This is something that will need to be confirmed empirically, however, for now we have an approximation of hand space which we can begin to work with.

Within this space a point represents an experience of a hand (Clark, 1993, p. 79). Any two stimuli which elicit the same point in the space are indiscriminable, that is they are experienced by the subject as the same (Clark, 1993, p. 198), in this example as two identical photographs of a hand. When two stimuli can be consciously discriminated by the subject the experience of the stimuli are represented by distinct points in the space , with, as above, the distance between the two points representing the perceived relative similarity of the stimuli. In other words, the similarity between the subject’s experiences of the stimuli.

Dimensions in quality space represent the ways in which experiences can be distinguished (Clark, 1993, p. 197 and Chapter 4). In our approximation of hand space we need to be a little more circumspect. Because we used only a small subset of hands (and thus experiences of hands) the number of dimensions which came out will be those which are most useful to subjects for judging the relative similarity of the hands which we used. For the first set of hand images we used subjects made their judgements based on (i) the gender and hairiness of the hands, (ii) the position of the thumb and (iii) the spacing of the fingers. Once the image of a rubber hand was added subjects were more reliant on (iv) the thickness of the fingers than (v) the spacing of the fingers in making their judgements. This is likely because that attribute was more useful for distinguishing the rubber hand from the set of hands we happened to employ.

We have from this experiment a description of the experience of (a small subset of) images of hands, which we are using as an approximation of the experience of the corresponding set of hands. It would be extremely long winded to write out the description in propositional form. We would need to specify each point solely with reference to its distance from other points (Clark, 1993, pp. 179–184). Ultimately on such accounts this is how experiences are defined, as a place in the quality space (Clark, 1993, p. 198).

When it comes to the feeling of embodiment, the hypothesis is that the feeling is carried by a subset of points in the space. Those which are on-line representations of hands which are sufficiently close to an offline prototype as to match it. Not in the sense of being indiscriminable from it, but in the sense of being close enough in quality space to it for the mind (i.e. further computations) to treat them as of the same type. The sense of embodiment is felt property of hands represented by on-line representations in, and only in, this region of hand space . Next, I move onto an understanding of offline body representations in terms of a conceptual space .

4.4 OffLine Body Representations as Prototypes in the Conceptual Space Defining the ‘Usual’ Body

The central distinguishing feature of the model I present in this paper is the offline body representation (first presented in Carruthers, 2008b; but see also De Preester & Tsakiris, 2009; Tsakiris, 2010) and the process of matching on-line and offline body representations. On the model being put forward here, the offline body representation is required for the sense of embodiment to be elicited for a perceived body. It plays a key role in the formation of the RHI. In order to understand this model, therefore, we need to spend some time understanding this kind of representation, in particular its representational content and how such content is matched to an on-line body representation.

In order to understand the computational work being done by such representations we need to know the representational content of offline and on-line representations. On-line representations are thought to represent the current state of the body such as the orientation of the limbs and head, what action the body is currently performing and the like. In contrast, offline body representations are thought to represent the body as it is usually including, for example, a generic body plan or perhaps even the actions afforded by the body (Carruthers, 2008a, pp. 1322–1323; 2008b, pp. 1305–1308).[5]

Here I present the hypothesis that offline body representations are points corresponding to prototype body arrangements within a particular conceptual space . Each point in this space represents a possible arrangement of one’s own body, with the distance between these points corresponding to the similarity between the represented arrangements. At this stage the way distance between points is defined is not known, and cannot be known a priori. The space forms a region of what we may call ‘body space ’, a conceptual space within which points represent bodies regardless of whether or not they are one’s own. At least one point in this space will represent a prototype or ‘typical’ arrangement of one’s own body.[6] Such points constitute offline body representations. The distance from this point to the point representing the body on-line , as it is now, corresponds to the similarity between the current arrangement of the body and a prototypical arrangement.

On-line body representations are also points in this space . A particular arrangement of a body is represented on-line when the corresponding point in this conceptual space is occurrently elicited. On-line body representations are thereby concrete particular vehicles, whereas offline body representations are abstract points in this space . They need never be realised. Indeed they might not represent any actual body arrangement (Gärdenfors, 2000, p. 87). It is the on-line representations which are actually tokened.

4.5 The Process of Matching

Now that I have presented a hypothesis as to the representations needed by a cognitive system to experience the rubber hand illusion, and introduced conceptual space representations, I focus on what I take to be the key step in eliciting the illusion, namely the matching of offline and on-line body representations. This, I propose, is to be understood with reference to conceptual spaces . On this account matching is determined by the similarity between the contents of on-line and offline body representations. This similarity corresponds to distance in body space .

Understanding matching in terms of distance in a conceptual space allows us to make sense of how the sense of embodiment varies in different version of the illusion and to make sense of ambiguous reports given in some versions of the illusion. From Tsakiris and Haggard (2005) it appears that orientation and shape of the hand are important for determining how closely the on-line representation falls to the offline prototype. Using only stationary models, they compared attempts to elicit the illusion using a rubber hand aligned parallel with the subject’s real hand, a rubber hand placed orthogonally to the real hand, a rubber hand appearing to be contralateral to the stimulated hand and a stick in place of the rubber hand. The orthogonal rubber hand was positioned such that were one’s hand to be in that position one would be reaching their left arm across the body and bending their hand back so as to be pointing left. This is, of course, an impossible position for the hand to be in. They used only a measure of proprioceptive drift as an index of the presence of the illusion, which may be problematic: however, the key findings of this study have been replicated using questionnaire measures (Tsakiris, Carpenter, James, & Fotopoulou, 2010). Drift was calculated as the difference between the judged location of the finger before and after stimulation, and the illusion was considered to be present if there was significantly greater drift toward the model after synchronous touching than there was after asynchronous touching (Tsakiris & Haggard, 2005, pp. 81–82). This difference was used rather than the difference in perceived location before and after stimulation, as subjects tend to mislocate their fingers as closer to the midline of the body than they are after holding them in a fixed position for some time.

Only where the rubber hand was ipsilateral to the stimulated hand and positioned parallel to it was there greater drift toward the model after synchronous rather than asynchronous touching (Tsakiris & Haggard, 2005, p. 82). No difference in drift was observed between synchronous and asynchronous stroking for a rubber hand placed orthogonally to the real hand, a contralateral hand or a stick (Tsakiris & Haggard, 2005, pp. 82–83).[7] Tsakiris and Haggard’s (2005) results suggest that the illusion is eliminated by implausibly orientated model hands or non-hand-shaped objects. In a follow up study the illusion was found to be inducible only for a realistically shaped model hand and not for vaguely hand shaped wooden blocks. This held using both questionnaire and drift measures of the illusion (Tsakiris et al., 2010).

That being said there is some flexibility in what can be represented as a body part. That is, there is some flexibility in what can be matched to an offline model. Short and Ward investigated the strength of the illusion for virtual objects with differing degrees of similarity to the subject’s arms. This is seen in studies using a somewhat different measure of the RHI, namely differences in reaction times to on versus off object visual stimuli. Short and Ward (2009) begin with the observation that subjects respond more quickly to visual stimuli presented on their hand than in peripersonal space around the hand (Short & Ward, 2009, p. 1092; see also Hari & Jousmaki, 1996). Such an effect is observed only for one’s own hand or for hand-shaped objects experienced as one’s own: it does not occur for hand shaped objects not experienced as one’s own (Short & Ward, 2009, p. 1092; see also Whiteley, Spence, & Haggard, 2008 and below). Indeed, it was found that responses were faster when the visual stimulus appeared on the virtual finger than next to it (Short & Ward, 2009, pp. 1094–1095). When the virtual hands were repositioned so as to appear to be 0.50 m in front of the subject rather than in the same space as the real hands, overall mean reaction times were longer for this task than the initial version, and again the difference between these reaction times is significant (Short & Ward, 2009, p. 1096). Short and Ward also altered the virtual object used in place of the virtual hands. The virtual hands were replaced by virtual hands being mirrored to the subject’s perspective (with the tips of the index fingers overlapping), virtual feet or white cones. Again, subjects responded faster to visual stimuli presented on the model than off (Short & Ward, 2009, p. 1098). This suggests that non-hand-like objects can be treated to some extent as one’s own in the active RHI. This seems consistent with subject’s questionnaire reports. In particular, whilst subjects tended to agree with the statement “I felt as though the virtual hands were my hands” in the initial set up, when they were asked about the white cones subjects responses averaged 3 on a 5 point scale, indicating that they were unsure as to whether or not they had an experience of embodiment in the cones (Short & Ward, 2009, p. 1100). In addition, as Short and Ward did not compare responses given synchronous and asynchronous feedback we cannot rule out the possibility that an ‘unsure’ response here is due merely to subjects’ suggestibility. As such it is not obvious whether or not the active RHI proper was experienced for this condition. It seems, however, that what we see for this version of the active RHI is a weakening, but not elimination, of the illusion by making the model less hand-like. This is suggested by both questionnaire and on versus off object reaction times.

This variation can be understood on the model presented here if the offline body representation is a prototype of one’s own body. That is, as the point at the centre of a quality space, where each point in that space represents a possible layout of the body. As with all prototypes, to match it is to fall close enough to it in conceptual space . Exactly what ‘close enough’ to the prototype means is impossible to know a priori, as the metric of the space is not known and must be discovered empirically. Additionally, it will be difficult to define, as the edges of the conceptual space will be fuzzy (Gärdenfors, 2000, pp. 71, 84) and potentially very large, especially if the relationship between similarity of body arrangements and distances in conceptual space is exponential rather than linear. Points inside this fuzzy region may represent something which tends not to exist, for example a gender-neutral face is represented by points in conceptual space bordering male and female subregions in face recognition networks (see Churchland, 1995 for an introduction; see O’Brien & Opie, 2000 for representational analysis). The subjective weakening of the illusion in Short and Ward’s study suggests that the on-line representations of the mirrored hands, virtual feet or white cones fall close to such a boundary. To the mind they move in synchrony with the real hands, so they are close to the prototype of one’s body, however, they are not shaped like one’s hands, so they are far from the prototype of one’s body. The on-line representation of these models falls near enough to the offline body prototype to elicit something of a sense of embodiment. However, it is also near the boundary with space representing body arrangements which one’s own body could not take, so that the sense of embodiment is subjectively weak.

In general, then, we explain the elicitation of the sense of embodiment in terms of the matching of an on-line body representation to an offline body representation. In order to allow for variation in the strength of the illusion dependent on how body-like the object is, we can understand the matching process as simply a matter of falling close enough to a prototype body arrangement in conceptual space .

We can also draw inferences regarding which features of the body influence how closely an on-line representation falls to the offline prototype. Of course, synchronous touch is an important factor, but from the above, it also seems that if the on-line representation represents the body as moving as predicted then it will tend to fall closer to the prototype. If, on the other hand, it is represented as not shaped like the body it will tend to fall far from the prototype. Further, as Short and Ward were able to elicit something of an active RHI for mirrored hands, feet and white cones it may be reasonable to conclude that moving as predicted is a more important feature than shape. Because multiple sources of evidence contribute to the computation of a match or not, this account is able to accommodate more findings than other matching models (such as that offered by Tsakiris, 2010), which hold that violations of shape should always prevent the feeling of embodiment being elicited.

An unusual form of the illusion due to Ehrsson (2009) suggests that not everything we may expect influences the matching process. Perhaps surprisingly the number of hands is not a strong factor influencing the matching process, or rather is a factor which is not as strong as the synchrony of touch. It seems, intuitively at least, that an on-line model representing a body as having two right arms should not fall close enough to the offline prototype to elicit the illusion for most people, as is suggested by reports discussed above which indicate that typically the real hand disappears—subjects do not experience themselves as having two hands. That is, subjects do not typically experience their own hand and the rubber hand together. However, the illusion can be modified to produce an experience of multiple hands. Ehrsson used two rubber hands in view and stroked both in synchrony with the subject’s real (hidden) hand and used a skin conductance response to the rubber hands being stabbed with a needle to measure the presence of the illusion. A greater skin conductance response was seen for both hands following synchronous stimulation than was present for asynchronous stimulation (Ehrsson, 2009, p. 311). Additionally, some subjects spontaneously reported feelings of embodiment in both rubber hands simultaneously (Ehrsson, 2009, p. 310). Unfortunately, the vividness of the illusion was not compared to the normal case, so we cannot be sure the illusion is as vivid in this case as it is in the single arm case.

Folegatti, Farnè, Salemme, & de Vignemont (2012) did compare the strength of the illusion in a two rubber hand condition to the strength of the illusion in a single hand condition. Their set up was different than Ehrsson’s in that the two rubber hands were not positioned next two each other. Rather one hand (the close rubber hand) was positioned 0.15 m from the participant’s real hand, with the other (the far rubber hand) 0.30 m from the participant’s hand (Folegatti et al., 2012, p. 802). They found that, whilst the sense of embodiment was not reported to be lower overall when both rubber hands were stimulated in synchrony with the real hand than when only one was, that this was likely due to a higher sense of embodiment for the close rubber hand than the far (Folegatti et al., 2012, pp. 807, 809). In other words, although the sense of embodiment was induced in the two rubber hand condition, the strength of the experience was still subject to variables such as distance (and thus posture). This adds weight to the idea that multiple factors are involved in matching on-line representations of hands to offline prototypes, but still leaves us with the surprising result that the sense of embodiment can be elicited for two rubber hands during the same trial.

Having just one hand on each side may not be as important to the offline prototype as it intuitively appears. Certainly, seeming to feel touch in a rubber hand will be a very strong factor influencing the illusion, as one never experiences touch coming from non-body objects. The synchrony of seen and felt touch should shift the on-line representation close to the offline prototype. Further, there is reason to think that experiences of embodiment in duplicate body parts are not as uncommon as we may expect. Following amputation or stroke patients will commonly experience phantom limbs or supernumerary limbs. It happens that some patients experience more than one phantom or supernumerary limb simultaneously (Lacroix, Melzack, Smith, & Mitchell, 1992; Srivastava et al., 2008). Additionally, subjects can experience their own limbs and supernumerary limbs simultaneously (Vallar & Ronchi, 2009) or multiple supernumerary limbs (Brock & Merwarth, 1957, p. 368). Patients feel embodied in all the phantoms or supernumerary limbs. In the case of the RHI, the similarity of each rubber hand and the offline model (shape, arrangement and tactile stimulation) and importantly the synchrony of felt and seen touch may push the on-line representation of each closer to the offline prototype more than the fact that two hands are seen pushes them away. In order to test this, we will need a detailed description of body space , something which has yet to be discovered.

4.6 Summary

On this model we have a qualitative account of what representations are used to elicit the RHI. Sensory information classed as related to some body or not is unified into an on-line body representation of the perceived body. If that body is represented as the same body represented by the stored offline body representation, then the sense of embodiment is elicited. Such a match involves the on-line body representation falling close to the offline prototype. Factors influencing whether or not the on-line representation matches the offline representation are the synchrony of touch, whether or not any proprioceptive or touch information comes from the body represented on-line, whether the body represented on-line is shaped and arranged as one’s body could be, and whether or not the body represented on-line moves as predicted. The RHI occurs when the rubber hand is mistaken for the real hand as represented in the offline model. This is due to an illusory experience of touch coming from a hand which is shaped and arranged in a way which is plausible for one’s own body as represented offline or that moves as predicted. If offline body representations are prototype points in body space , then we can understand variations of vividness observed when varying these factors as due to the formation of on-line body representations at variable distance from the offline prototype in body space .

We also have a hypothesis about the representation which limits the RHI to just certain objects. It is an offline representation which has as its content the body as it usually is. This consists of a prototype body arrangement and a conceptual space surrounding this prototype representing possible arrangements of the body. Particularly important to this representation are the body’s shape and orientation, and the fact that it moves as predicted.

4.7 The Loss of the Sense of Embodiment in Somatoparaphrenia

This hypothesis regarding the erroneous sense of embodiment elicited in the RHI can also be applied to the loss of the sense of embodiment in somatoparaphrenia. In somatoparaphrenia the sense of embodiment is not elicited for a real body part as normal. One place to look for an explanation of this is in problems matching on-line representations of the targeted body part to the offline prototype.

One possibility is that those suffering somatoparaphrenia have lost an offline prototype of the targeted limb. Perhaps the damage caused by stroke has simply wiped away the neural network(s) used to represent that part of body offline. If the targeted body part is no longer represented offline then it can’t be matched to an on-line representation of that body part and so the sense of embodiment cannot be elicited. This is unlikely, however, as many of those suffering from somatoparaphrenia also suffer from anosognosia for hemiplegia. As per Chapter 3 this suggests they possess an intact, but outdated, offline prototype of the targeted body part.

Another possibility is that the target arm cannot be represented on-line, as might be suggested by the association between somatoparaphrenia and hemi-spatial neglect. Perhaps due to neglect of the left half of space , patients lack the capacity to form on-line representations of their left arm and hand, say, thus preventing a match between on-line and offline representations of the arm. As we have seen, however, placing the targeted limb into non-neglected space , thus allowing on-line representations to be formed does not cause somatoparaphrenia to remit. Furthermore, this hypothesis would be unable to explain why there are patients who show neglect for the left half of space, but only deny ownership of some of their body, e.g. the left arm, but not the left leg.

In contrast, I hypothesise that the problem underlying the loss of the sense of embodiment characteristic of somatoparaphrenia is a problem with the process of matching on-line and offline representations of the targeted body part. Specifically, patients suffering somatoparaphrenia lack the capacity to use normal cues to produce a match. Although there are many ways which we can think of for this process to go wrong, here I will limit my comments to one case which is likely common to many cases of somatoparaphrenia associated with anosognosia for hemiplegia and one pilot study which suggests a helpful line of empirical enquiry.

As we have seen with the rubber hand illusion, the cue of a body part moving as predicted is an important cue for generating a match and eliciting the sense of embodiment. Yet the limb targeted by somatoparaphrenia is typically paralysed. This means that, at best, this cue has lost much of its potential influence, which, as we have seen, depends on fine grained temporal dynamics. What’s more, in cases where somatoparaphrenia is associated with anosognosia for hemiplegia it is possible that false predictions are made. As we saw in Chapter 3, at least a subgroup of those suffering anosognosia behave as if they expect their limb to move. When confronted with a limb that is not moving, whilst producing predictions of their limb as actually moving, there will be a mismatch between the on-line representation of the limb and the offline prototype. Depending on the availability of other cues this mismatch may well be sufficient to prevent the sense of embodiment being elicited. This needs testing, but prima facie it is consistent with the common co-occurrence of anosognosia and somatoparaphrenia.

This said, other cues must play a role in somatoparaphrenia. As we have seen, there are cases of double dissociations between anosognosia and somatoparaphrenia, and there may be some cases of anosognosia where the patients are incapable of forming predictions about the movement of the targeted body part.

It is likely that multiple cues to matching on-line and offline body representations are lost or misused in cases of somatoparaphrenia. This is suggested by what appears to be the overvaluing of one specific cue in a case of remitted somatoparaphrenia, and the corollary undervaluing of some common cues.

Van Stralen, Van Zandvoort, and Dijkerman (2011) report the case of GE. Immediately following a stroke GE suffered left hemiplegia and neglect, showed anosognosia for the plegia of her left arm and hand and attributed her left arm and hand to hospital staff (Van Stralen et al., 2011, p. 3146). Two weeks later GE no longer misattributed her left arm, but was observed often touching her left arm and hand with her right. She explained “that this was because she felt the stroking in the affected hand and this helped her to regard the arm as a part of herself” (Van Stralen et al., 2011, p. 3146). At this stage she also reported feeling self-generated touch in her left arm and hand, but not touch produced by another person (Van Stralen et al., 2011, p. 3147).

Van Stralen and colleagues performed further examinations in an attempt to determine if self-produced touch was affecting GE’s feeling of embodiment in her left hand and arm. GE was asked to stroke several arms and arm-like objects for 3 minutes and asked several times throughout the procedure if she felt the arm was her own or someone else’s. Reminiscent of the RHI she was asked to touch a left prosthetic arm and hand placed in an anatomically plausible location, a right prosthesis in the same location, an examiners arm in that same location and a left prosthesis in an anatomically implausible location. After some time GE came to self-attribute the prosthesis or arm in all four conditions (Van Stralen et al., 2011, p. 3147).

Although it would be preferable to use rating scales explicitly about the sense of embodiment, this erroneous self-attribution suggests that for GE the sense of embodiment could be elicited for other’s arms and prosthesis. Unlike what is seen for healthy subjects during the RHI it seems that this patient can elicit a sense of embodiment for prosthetic or other’s limbs even when that limb is in an anatomically implausible location, is contralateral and no touch is experienced in the real left limb. Active self-touch of a hand or arm shaped object may thus be an overvalued cue for the sense of embodiment for this patient. Overvaluing this cue may allow the remission of somatoparaphrenia, whilst making it too easy to elicit a sense of embodiment for foreign objects. This is not to say that other cues play no role in eliciting the sense of embodiment (ex hypothesi by influencing matching). Van Stralen and colleagues note that it took substantially longer for GE to begin to self-attribute the right prosthesis and the left prosthesis placed in an anatomically implausible location than either the examiners arm or left prosthesis in an anatomically plausible location (Van Stralen et al., 2011, p. 3147). This suggests that these cues still influence whether or not the on-line representation of the seen body part or prosthesis matches the patient’s offline prototype, but that their influence on producing a match or not is undervalued, at least compared to the information obtained from touching a hand/arm shaped object.

The overvaluing of information produced by active self-touch can be observed in patient GE in other conditions. GE was more likely to attribute her own real left arm and hand to others following active self-touch of a prosthesis, than she was following active self-touch of her real hand, or when an experimenter stroked her real hand (Van Stralen et al., 2011, p. 3149). In other words, she not only comes to attribute prosthetic hands to herself when she has been touching them, but she also comes to attribute her real arm and hand to others. This suggests that she has lost the sense of embodiment for her real left hand and arm just by stroking an arm shaped object.

In sum then, there is some reason to think that the loss of the sense of embodiment characteristic of somatoparaphrenia is due to an undervaluing of cues in the process of matching on-line and offline body representations. Somatoparaphrenia may remit when a replacement cue, in this case from active self-touch, is overvalued. It must be cautioned, however, that Van Stralen and colleagues’ study was explicitly exploratory. It dealt with a single patient, they did not compare the patient’s performance to patient or healthy control groups (although we know a lot about how healthy subjects respond to the rubber hand illusion) and they used a categorical measure of the sense of embodiment (self versus other attribution) rather than a rating scale. Categorical measures are commonly used when assessing ownership attribution in somatoparaphrenia, ultimately, however, a scaled measure will give greater power for comparing performance to healthy controls. None-the-less the result is promising and at the very least suggests a research program in examining what cues are used for the sense of embodiment following remission of somatoparaphrenia. However, whilst this motivates the idea that the matching in conceptual space hypothesis of the sense of embodiment is applicable to somatoparaphrenia, it does not provide experimental support for the hypothesis. For that, we must return to the rubber hand illusion.

4.8 Testing the Hypothesis

From this I believe we have a quite reasonable hypothesis to explain the feeling of embodiment in the rubber hand illusion. Although the hypothesis is well motivated, we don’t know if it’s true. To determine this, we need direct empirical tests of predictions made by the hypothesis. Fortunately, some of this work has been done.

Xiaoqing Gao, Regine Zopf, Rachel Robbins, Alicia Wilcox, and I (Carruthers, Gao, Zopf, Wilcox, & Robbins, 2017) have begun to test this account, specifically we attempted to determine if there was a conceptual space for hands and if the RHI changed the space in a manner that would be expected given this model. If this model is right, then there should be a conceptual/quality space for hands. What’s more, if this model is right, then the RHI should change this space in very specific ways. Most notably, during the illusion, the rubber hand should change position in this space so as to be closer to an own hand prototype. Unfortunately, the methods we have used to date haven’t allowed us to test this directly, largely because measuring individual conceptual spaces in a way that works well with the rubber hand illusion gives much less clear data than is obtainable for a group of subjects. However, the model also makes a prediction about how the rubber hand illusion will change the conceptual space for hands averaged across a group of subjects. During the illusion in virtue of becoming more like the subject’s hand the rubber hand should become more like (real) hands in general. As such, during the illusion the rubber hand should change location so as to be closer to a point representing a prototypical hand. Averaging conceptual spaces across a group of subjects might prevent us from having a measure of the prototype of each individual’s hand, but it does allow us to have a good measure of a prototype hand, i.e. the centre of the conceptual space.

We had subjects perform a series of odd-one-out judgements for triads of images of hands, including their own hand. From this we were (rather Xiaoqing was) able to obtain a three-dimensional space for hands. One dimension seemed to be a combination of how hairy the hands were and their apparent gender (hairy/male versus not hairy/female), the second the position of thumb relative to the rest of the hand (far versus near) and the third the size of the gaps between fingers (fingers pressed together versus fingers spaced widely apart).

Following this we added an image of a prosthetic hand to the triads and had subjects perform odd-one-out judgements after receiving either synchronous or asynchronous stroking on their own real hand (out of sight, under the screen onto which the images were projected) and the image of a prosthetic hand. Again, Xiaoqing obtained a three-dimensional space for hands. The inclusion of the rubber hand in the stimuli set seemed to change which dimensions subjects found most helpful for distinguishing the images as the third dimension of the space obtained in the second experiment was best interpreted as the thickness of the fingers themselves (thin versus thick), rather than their spacing. This was true for the space obtained in both the synchronous and asynchronous stroking conditions.

Importantly, however, there was a difference between the spaces obtained for the synchronous and asynchronous conditions. Specifically following synchronous stroking, the rubber hand was closer to the centre of the space than it was following asynchronous stroking. This confirms to one of the predictions of the model outlined here. During the RHI, the rubber hand is more like a prototypical hand. As our methods to date have focused on obtaining average conceptual spaces for groups of participants there are still many predictions to test and many open questions. The model predicts that the rubber hand will be closer to an own hand prototype during the illusion, than during asynchronous stroking. This needs to be tested using a method that allows for more robust measures of individual spaces and own hand prototypes.

That said, there is now evidence that the sense of embodiment is elicited (at least in the RHI) by matching an on-line body representation to an offline prototype that goes beyond the literature that motivated the model. Further there is an empirical research program for further testing and refining the model.

4.9 Conclusion

In this chapter, I have argued that the feeling of embodiment is carried by on-line body representations that match an individual’s offline prototype of what their body is usually like. When these representations and the process of matching are understood in terms of conceptual spaces the model can explain many features of the rubber hand illusion and is extendable to the loss of the feeling of embodiment in the delusion of somatoparaphrenia. Furthermore, the model makes testable predictions and the first experiments testing the model have provided positive results.

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Footnotes

1

Assuming the relevant conceptual space is convex. In the sense defined by Gärdenfors (2000, p. 69) a space is convex if, for any two points x and y in the space, any point which lies between x and y is also in that space (given the appropriate definition of betweenness for the metric of the space). If this holds, similarity is a function of the distance between the points and we need not specify direction.

2

I phrase these as questions to aid our understanding. Of course one should not think of the mechanism being described as literally asking questions of itself.

3

It is true that we only receive information about our own body proprioceptively. One might think this should be enough to elicit a sense of embodiment for a body part: but if so then illusions like the RHI would be impossible, so additional criteria must be used. However, I take it that this criterion prevents the sense of embodiment in a rubber hand from being as vivid as the sense of embodiment in one’s real hand.

4

Gärdenfors distinguishes spaces which correspond to (represent) properties and those which correspond to (represent) concepts. Properties correspond to a domain; that is, spaces defined by a set of ‘integral’ dimensions. These dimensions are integral in that it is not possible to assign a value to one without the others (Gärdenfors, 2000, p. 24), e.g. no object can have a brightness without also having a hue and saturation. In contrast. Gärdenfors supposes concepts are formed by spaces defined by the joining of domains such that some dimensions, say size, can be defined without assigning a value to others, say brightness. I will not make use of this distinction as it requires too great a degree of independence of properties, for example that colour be representable independent of shape, which is implausible (see e.g. Schier, 2007).

5

The on-line versus offline distinction bears some similarity to the distinction between the short term and long term body image put forward by O’Shaughnessy (1995). Although there are some close similarities between the two distinctions, with offline roughly corresponding to long-term and on-line to short-term, there are also some important differences. For example, O’Shaughnessy’s distinction is a distinction within the body image, whereas the on-line versus offline distinction is orthogonal to the image versus schema distinction. Second, O’Shaughnessy takes it that the long-term body image representations are a requirement for short-term ones. In contrast, here, no claims about the relationship between offline and on-line representations are being made (Carruthers, 2008a). Additionally O’Shaughnessy does not describe the short and long term body image in terms of conceptual space .

6

It may be that there is more than one prototype body arrangement, for example a prototype arrangement for a standing versus a sitting body. If so we may talk of a prototype space defined by such points rather than a single prototype point. This is a matter for discovery.

7

Interestingly drift in the asynchronous stroking condition was larger if the model was a hand arranged implausibly (e.g. orthogonally to the real hand) or a stick than if it were a plausibly arranged hand. However, as there was no difference in drift between synchronous and asynchronous touching for these models and the drift was always less than that seen for synchronous stroking using a plausibly arranged rubber hand, Tsakiris and Haggard deemed this finding unimportant and suggested it was merely an exaggeration of the tendency to report one’s fingers are closer to the midline than they actually are (Tsakiris & Haggard, 2005, p. 82).

© The Author(s) 2019

Glenn CarruthersThe Feeling of Embodimenthttps://doi.org/10.1007/978-3-030-14167-7_5

5. …And Then What Happens?

Glenn Carruthers[1]

(1) School of Psychology, Charles Sturt University, Port Macquarie, NSW, Australia

Glenn Carruthers Email: gcarruthers@csu.edu.au

This chapter makes use of substantially altered text previously published as: Carruthers, G. (2014).

5.1 Introduction

So far, we have a well-motivated hypothesis to explain the phenomenology of the feeling of embodiment that has received some independent and direct empirical support. But, is this an account of our consciousness of this feeling or just how the content is represented? In this chapter I pose what Dennett has called the “Hard Question” of consciousness. The above account undoubtedly does a good job of explaining how the representations of our own embodiment are elicited. But, how are we to distinguish conscious and unconscious representations of our own embodiment? This is not a problem we can ignore. I will briefly consider two possible answers to this problem known as vehicle and functionalist accounts of consciousness. In the next chapter I argue that neither kind of solution on its own can resolve the concerns raised by this problem. Instead each solution is to be understood as solving a different problem, one explaining the phenomenal qualities of mental states and the other explaining awareness of (or cognitive access to) those qualities. The solution to the problem of consciousness suggested by our investigation is ultimately a hybrid functionalist and vehicle account of consciousness.

5.2 Unconscious and Conscious Representations of Embodiment

It would, I take it, be bizarre if there were no on-line representations of one’s own body that where, in some sense, unconscious. It may be possible to deny this based on introspection. Perhaps it seems that the sense of embodiment is always present and so the on-line representation carrying this feeling is always conscious. I always feel that I am my body, but despite, or perhaps because of, the ubiquity of this feeling I rarely attend to it. It is a background feeling. However, introspection gives us poor grounds to assume that there is a ubiquitous feeling of embodiment.

What would lead one to assume that the feeling of embodiment is ubiquitous? We can see where this assumption comes from, and how poorly grounded it is, by an analogy with visual consciousness. Recall our favoured example purporting to show that we are not conscious of as much as we think we are from Dennett (1991), that I introduced back in Chapter 1. In the playing cards example, you were asked to stare at a point on a wall in front of you, randomly select a playing card, and gradually move it toward the centre of your vision. Recall, that the typical finding is that it is only about 2 or 3 degrees from the point one is looking at that the colour and identity of the card become identifiable (Dennett, 1991, p. 54). One reason people find this kind of example surprising is that whenever one looks to see what object is in one’s periphery one finds it clear, distinct and coloured. As such we tend to assume that we always experience those objects as such. This claim provides us with a useful analogy for understanding why it seems like a feeling of embodiment is ubiquitous. The representation of one’s own embodiment could be unconscious but, because the representation is always being formed, it is there whenever we go “looking” for it, or more generally when it is expected to occur to the subject, i.e. consciously. Just as objects in our periphery always appear clear, distinct and coloured when we go looking for them, our representation of embodiment is always experienced when we go looking for it, thus meeting our expectations. Just as this may lead us to believe that objects in our periphery always appear clear, distinct and coloured, this may lead us to believe we always experience of our own embodiment waiting it the fringes of consciousness to be attended to.

We have little grounds for assuming that our own embodiment is always consciously represented, so what then is the difference between conscious and unconscious representations of our own embodiment, i.e. what is the difference between an unconscious and a conscious on-line representation of one’s own body?

5.3 The Hard Question

We have here another question about accounts of the sense of embodiment, a question Dennett calls the ‘Hard Question’ (not to be confused with any purported ‘Hard Problems’ that we met in Chapter 1 [Chalmers, 2002]): after the on-line body representation is elicited and matches the off-line prototype, well, then what happens (Dennett, 1991, p. 255)? What is the difference between a representation of my own body of which I become aware and one that languishes forever in the apparent irrelevance of unconsciousness?

The analogy employed above of “looking” for one’s body suggests one possible answer. Perhaps an unconscious representation of the own body becomes a conscious representation when the subject’s attention is directed to it? In the following section I consider and discuss this possibility. Having found this wanting, I consider a further possibility, that the answer to the Hard Question is that the representation enters into the mechanisms required for verbal report. I argue that this answer is also unsatisfactory, as it is inconsistent with behavioural evidence of a sense of embodiment in non-verbal animals. These first two options are ‘functionalist theories.’ They propose that consciousness is constituted by representing vehicles playing a certain role in cognition. Although these two specific proposals seem to fail on empirical grounds it is important to note that other functionalist theories, notably those that identify consciousness with multiple functional roles remain open. Finally, I propose a radical alternative suggesting that the answer to the Hard Question is to be found not in the uses to which representations are put within a cognitive system, but in the nature of the representations themselves. Such a view is known as a ‘vehicle theory .’ Regardless of which of the two research agendas individuals chose to pursue, it is clear that we do not have an answer to the Hard Question for the sense of embodiment. In the following chapters I argue that both kinds of approach are needed to answer different questions about the experience of embodiment.

5.3.1 Attention

One potential answer to the Hard Question is attention

. Such an answer is suggested by well-known cases of in-attentional blindness, where subjects fail to see perfectly obvious stimuli (like a woman in a gorilla suit) simply because their attention is directed elsewhere (Mack & Rock, 1998). More specifically, let us hypothesise that the difference between an unconscious representation of embodiment and the conscious feeling of embodiment is that the conscious representation is attended to. If this is true, then we would have a clear research agenda: understand how and why an on-line body representation is selected or not selected for attention and understand the mechanisms of attention.

Such a view has not been developed in detail for the feeling of embodiment. Notwithstanding, attention based accounts of consciousness do have some currency in the explanation of perceptual consciousness. Prinz (2000, 2012), for example, advocates such a view. Unfortunately, evidence is mounting that attention is not a good answer to the Hard Question, at least not on its own, as attention is not sufficient for consciousness. That is, subjects can attend to things of which they are not conscious. Here I discuss one well-studied example.

Norman, Heywood, and Kentridge (2013) have provided compelling evidence that subjects can visually attend to objects, namely two-dimensional shapes, even when they cannot consciously see those objects. They start from prior observations of the effects of taking two-dimensional shapes as the objects of attention in colour discrimination tasks. In these tasks, subjects are asked to indicate with a button press the colour of a circle. Before the target coloured circle appears, a supraliminal spatial cue is presented. In the trials of interest here the cue appears some distance from where the target circle will ultimately be shown. However, it may appear in the same shape as the cue or a different shape. See Fig. 5.1 for an example layout.

Fig. 5.1

The spatial layout of the stimuli. In the centre, we see a fixation cross, left and right are two rectangles. A cue appears at the x and disappears, followed by a target at one of the two circles. The subject’s task is to indicate the colour of the target. Subjects respond faster to cues appearing within the same shape as the cue, even though they are as far from the cue as the target in the other shape (Courtesy of Glenn Carruthers)

When the target appears in the same object as the cue, response times are facilitated (Egly, Driver, & Rafal, 1994). Norman and colleagues take this as characteristic of attention to such shapes.

Norman and colleagues repeated this experiment but made the shapes invisible. They presented on a screen an array of Gabor patches whose orientation rapidly alternated between vertical and horizontal. Within the array rectangles were defined by Gabor patches flickering out of phase with the remainder of the array (Norman et al., 2013, p. 838). When the background patches were vertical, those defining the rectangle were horizontal, and vice versa. Observing the array, subjects reported seeing flickering Gabor patches, but were unable to see the rectangles. Indeed, subjects were no better than chance when asked to guess whether or not such flickering displays contained rectangles (Norman et al., 2013, p. 840). Despite the invisibility of the shapes there was a facilitation effect in the colour discrimination task characteristic of attention being directed at the shapes. That is, subjects were faster at responding to targets which appeared in the same shape as the cue, than for targets which appeared the same distance from the cue but in a different shape (Norman et al., 2013, p. 839).

In this study, we see an effect characteristic of attention being directed at an object, despite the object being invisible. This demonstrates that subjects can attend to shapes of which they are not conscious. In general, this also suggests that attention is not sufficient for consciousness. Without a reason to think that the feeling of embodiment will be an exception to this, it seems unlikely that attention will answer the Hard Question for the feeling of embodiment.

5.3.2 Reportability

Often, we take it that we can be confident that a subject experiences something if they are able to verbally report it. Although such reports are susceptible to a variety of introspective omissions and commissions (Dennett, 1991, p. 96; Schwitzgebel, 2008), in practice, verbal reports (especially questionnaire responses) are very often treated as the best way to operationalise experience. Indeed, the theories of the feeling of embodiment that I’ve discussed in previous chapters are built on studies using questionnaires to ask subjects to report their experiences of embodiment. At the heart of this approach lies an intuition that, however imperfectly, we are able to talk about those things that we experience, but not those things that reside in our unconscious minds. This intuition suggests an approach to the Hard Question: perhaps the difference between conscious and unconscious representations is just that conscious representations are available for report. Although such an approach would be highly controversial (Block, 2007), there is no approach to the Hard Question that is not controversial, and this proposal remains live.

That said, we do have strong reason to doubt that it is reportability that distinguishes conscious and unconscious representations of embodiment, as there are many non-verbal animals that display evidence of experiencing a feeling of embodiment. This suggests that being available for verbal report is not necessary for a conscious feeling of embodiment.

Good evidence for this comes from the mirror self-recognition test. This test, first proposed by Gallup (1970), involves marking an animal surreptitiously (usually when anaesthetised) with a non-irritating, odourless dye on a part of the animal’s body that cannot be seen without a mirror (such as the forehead). An animal is deemed to pass the mirror self-recognition test if there is a significant increase in mark directed behaviour coincident with the animal observing itself in the mirror (Gallup, 1970, p. 87). Such behaviour indicates that the animal has recognised itself in the mirror as it uses the mirror to direct actions towards itself. A feeling of embodiment is needed to pass such tests. To learn to recognise oneself in a mirror one needs to realise that the actions one sees in the mirror are equivalent to the actions one is currently performing (Povinelli, 2001, p. 85). This depends on a variety of things, such as the sense of agency, but also a feeling of embodiment. Without a feeling of embodiment, the subject can’t recognise their own real body as their own and so would be unable to recognise the image in the mirror as an image of their own body. As such, passing the test is good evidence for a feeling of embodiment (but, of course, failing to pass the test is not evidence of a lack of a feeling of embodiment).

Where this creates a problem for using reportability as an answer to the Hard Question is in the fact that many non-verbal animals pass the mirror self-recognition test. This includes chimpanzees (Gallup, 1970), orang-utans, human raised gorillas (Povinelli & Cant, 1995), bottlenose dolphins (Marten & Psarakos, 1994), and European magpies (Prior, Schwarz, & Güntürkün, 2008). These animals thus show evidence of experiencing a feeling of embodiment. As such, verbal report does not seem necessary for consciousness, and thus investigating how unconscious on-line body representation becomes available for verbal report is a non-starter as a solution to the Hard Question.

The solutions considered so far to the Hard Question are examples of “functionalist” or process theories. They posit that for a representation to be conscious is for it to be used a certain way, say be being attended to or by being made available for report. On such views, it is use which constitutes consciousness. Whilst the two options considered here do seem like non-starters, there are other functionalist theories available. Other accounts, such as Dennett’s multiple drafts model (1991) or Baars’ global workspace (1988), suggest that consciousness is not a single use within a cognitive system, but rather a conglomeration of many uses and these options remain live. I will have more to say about the prospects for a multi-function account in coming chapters. Next, I turn to a theoretical basis for approaching the Hard Question that offers a fundamentally different kind of solution to the options considered so far.

5.3.3 Vehicle Theories

Vehicle theories of consciousness answer the Hard Question in a rather different way. The key issue we are getting at is: what is the difference between an unconscious and a conscious representation of embodiment? The proposals considered thus far have followed Dennett in hypothesising that this is a difference between how unconscious and conscious representations are processed (e.g. are they subject to attention or made available for verbal report?) In other words, the difference is a matter of what is done with the representation. Such approaches are functionalist theories in that they consider the particular use of a representation within a cognitive system to constitute that representation being conscious.

Vehicle theories, in contrast, hypothesise that the difference between conscious and unconscious representations is not how they are processed, but in the nature of the representation itself (O’Brien & Opie, 1999, p. 128). The nature of conscious vehicles of representation (also known as representation bearers) is hypothesised to be different to the nature of unconscious representing vehicles. On such views consciousness is a way of representing the world using different kinds of vehicle than those used by unconscious representations. According to vehicle theories the answer to the Hard Question is not “and then some additional processing occurs” but rather, “and then the vehicle of representation is changed from one form to another.”

O’Brien and Opie propose a general answer to this question making use of distinctions in kinds of representing vehicles offered by Dennett (1982). In particular they focus on a distinction between ‘explicit ’ representations which are: “physically distinct objects, each possessed of a single semantic value” (O’Brien & Opie, 1999, p. 133) and ‘potentially explicit ’ and ‘tacit ’[1] representations which are to be understood in terms of a computational system’s capacity to make certain information explicit in the above sense. In general, O’Brien and Opie hypothesise that we are conscious of all and only things that are represented in an explicit form. All unconscious representations would then take the form of potentially explicit or tacit representations.

According to this version of a vehicle theory, a conscious feeling of embodiment would be an explicit representation of embodiment. That is, a discrete vehicle, such as a stable pattern of activity across a layer of neurons (O’Brien & Opie, 1999, p. 138), with that content. On the hypothesis argued for so far in this book it would be part of the content of a certain subset of on-line body representations in conceptual body space , i.e. those which match an off-line prototype . An unconscious representation of embodiment would not be a discrete vehicle, but a disposition in the cognitive system to produce such a representation.

If such an approach is correct then we have a new way to approach the Hard Question for the sense of embodiment. How are on-line body representations made explicit ? Why is it the case that it is sometimes not made explicit? Is this a matter of the subject metaphorically “looking for” it, if so, how would that be understood more literally?

The benefit of taking this approach is that it offers a new kind of answer to the Hard Question by offering a new conception of what properties of a computational system distinguish conscious from unconscious representations. In addition, a research agenda is set: why and how are on-line body representations sometimes made explicit ?

5.4 Conclusion

In this chapter, I have introduced the “Hard Question” for the feeling of embodiment, what happens after embodiment is represented to make it conscious? So far, I have argued that the feeling of embodiment is underlain by on-line body representations which fall close enough to an off-line prototype in a conceptual body space . This has afforded an explanation of how the feeling of embodiment is elicited in the rubber hand illusion and why it is lost in somatoparaphrenia. But, we may worry, is this an account of the feeling of embodiment or just how we represent our own embodiment? There are two broad hypotheses in response to this worry. The first, functionalist, response hypothesises that whilst such an account explains how we represent embodiment it does not explain how it is felt. Instead that is a job for how the representation of embodiment (i.e. certain on-line body representations) are used in the rest of the cognitive system. Although some specific single function type accounts fail on empirical grounds, more promising multi-function approaches remain to be considered. In contrast, vehicle accounts suppose that in explaining how embodiment is represented (in on-line representations that match off-line prototypes) we have explained how embodiment is felt, because the feeling of embodiment is to be identified with representing embodiment in the right way (e.g. explicitly in O’Brien and Opie’s sense). In the next chapters I will consider evidence for specific versions of these approaches. Ultimately, I will conclude that a vehicle theory is right in that the conceptual/quality space account considered so far explains the phenomenal qualities of the feeling of embodiment, but that a multi-function approach, such as Dennett’s multiple-drafts hypothesis is needed to explain the appearance of those qualities to the subject.

References

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Block, N. (2007). Consciousness, accessibility, and the mesh between psychology and neuroscience. Behavioral and Brain Sciences, 30(5–6), 481–499.Crossref

Carruthers, G. (2014). What makes us conscious of our own agency? And why the conscious versus unconscious representation distinction matters. Frontiers in Human Neuroscience, 8, 434. https://doi.org/10.3389/fnhum.2014.00434.

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Marten, K., & Psarakos, S. (1994). Evidence of self-awareness in the bottlenose dolphin (Tursiops truncatus). In S. T. Parker, R. W. Mitchell, & M. L. Boccia (Eds.), Self-awareness in animals and humans: Developmental perspectives (pp. 361–379). New York, NY: Cambridge University Press. http://dx.doi.org/10.1017/CBO9780511565526.026.

Norman, L. J., Heywood, C. A., & Kentridge, R. W. (2013). Object-based attention without awareness. Psychological Science, 24(6), 836–843. https://doi.org/10.1177/0956797612461449.Crossref

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Footnotes

1

There are differences between ‘potentially explicit ’ and ‘tacit ’ representations. These differences become important when we consider the kinds of computations being performed within a cognitive system, but won’t play a role in this short statement of O’Brien and Opie’s hypothesis regarding consciousness (indeed O’Brien and Opie argue that a Vehicle Theory could only be true for connectionist systems and that the ‘potentially explicit ’ versus ‘tacit ’ distinction does not apply to such systems).

© The Author(s) 2019

Glenn CarruthersThe Feeling of Embodimenthttps://doi.org/10.1007/978-3-030-14167-7_6

6. Implications of the Real Problem of Consciousness for the Sense of Embodiment: We Need a Hybrid Account of ‘Consciousness’

Glenn Carruthers[1]

(1) School of Psychology, Charles Sturt University, Port Macquarie, NSW, Australia

Glenn Carruthers Email: gcarruthers@csu.edu.au

6.1 Introduction

The Real Problem of consciousness is the problem of explaining experience. Using the feeling of embodiment as a case study, I have ended up with a hypothesis that a body feels like mine if an on-line representation of that body is elicited in the right region of body space such that it matches an off-line prototype. As proposed by Clark (1993) phenomenal qualities are identified with (and explained by) regions of quality spaces. In this case, body space . This, we have seen, has explanatory power when applied to how the feeling of embodiment changes in the rubber hand illusion and the delusion somatoparaphrenia. This account also makes testable predictions, some of which have been confirmed.

As it turns out this cannot by the whole story. I don’t just mean that we don’t know enough about the quality space for bodies—currently we have only one estimate of hand space . Beyond this, the conclusions drawn so far depend in large part on reports from patients suffering from somatoparaphrenia and anosognosia for hemiplegia. I have yet to address difficulties with the Real Problem regarding these experiences. Do we have enough convincing evidence such that we can say we know what these patients experience? Returning to issues outlined in Chapter 1, the question is: are patients’ reports valid measures of their experiences?

The problem we face here is an issue of distinguishing confabulations from veridical reports. In its most general sense, confabulation is “an erroneous statement made without conscious effort to deceive” (Feinberg & Roane, 1997, p. 73). This is more general than other definitions of confabulation in the literature, particularly those tied to amnesia. This needn’t concern us here. What worries me is the possibility of confabulated reports of experience, or, people reporting experiences they didn’t actually have, yet sincerely believe they had.

We have already seen in Chapters 2 and 3 that we have reason to worry about such confabulations in cases of anosognosia and somatoparaphrenia. For example, patients suffering anosognosia often seem to produce “provoked confabulations” in response to examiners questions about their failures to move. Some of the statements such patients make refer to experiences such as stiffness or fatigue. Do such patients experience fatigue and stiffness, or are these experiences only represented in the story they tell to try and make sense of their failure to move? What about those who say they have moved?

This phenomenon alone gives reason enough to worry about the possibility of confabulated reports of experience in such cases. It seems that whatever our theory of consciousness is, it must be compatible with the possibility that at least some of these reports are confabulations. Why does it matter if some reports from patients are confabulated and some are veridical? Ultimately it matters quite a lot for our explanations of patients’ experience. Whatever patients say about their experiences requires explanation, but, intuitively at least, we’d expect that the explanation will be different for veridical reports than for confabulations: only one will make reference to experiences which are the same to an observer as what is reported by the patient.

A helpful way to think about this, as I (2018) have argued previously in attempting to understand out-of-body experiences, is to think about individual differences (variation) in the reports of patients. Whilst there is something in common to reports and behaviours of all patients suffering from anosognosia or somatoparaphrenia that allows us to classify them as suffering particular symptoms, no two patients say exactly the same things about their experiences. Do we explain this as variation in experience or variation in confabulations, specifically stories told to make sense of bizarre experiences, or both?

Once we ask this question, we quickly find ourselves in a rabbit warren of issues that raise concerns about the sufficiency of a quality/conceptual space account of the feeling of embodiment. My plan is thus: I will have a quick look at some of the common ways in which experiences of anosognosia and somatoparaphrenia seem to differ between patients. Following this I return to a quality space account, along with the more general class of hypotheses that this fits into, the vehicle theories introduced last chapter. However, I argue that such accounts cannot accommodate confabulations. This may not be a disaster for vehicle theories if we can explain away apparent confabulations. There are a range of hypotheses to explain the observed variation in reports from patients suffering from somatoparaphrenia and anosognosia. At either end of this range are two extremes: (1) That all patients share a minimal core experience that defines the disorder, but each tells a different story to make sense of it and all the variation in reports is to be explained by variation in confabulations (call this the core phenomenology plus confabulation hypothesis); and, (2) That patients have very different experiences and all of the variation in their reports is explained by variation in their experiences (call this the elaborate phenomenology hypothesis). If (2) is correct then a vehicle account could provide a complete account of patient experiences.

It is difficult if not impossible to find evidence that favours the elaborate phenomenology hypothesis over the core phenomenology plus confabulation hypothesis. This surprising state of affairs is predicted by Dennett’s multiple drafts account of consciousness. Moreover, how such evidence is interpreted seems to depend on our prior commitments to either a vehicle or functionalist theory . Given the difficulties vehicle theories have in accommodating confabulations, perhaps we should take the account offered so far as an account only of how we represent our own embodiment and not of how we experience it? That is, as a conceptual, but not quality, space account? To that we could add a Dennettian processing account to explain how subjects become aware of that content (“then what happens?”)?

The problem with this sort of solution is that Dennett’s account faces some well-known objections, which are particularly relevant to the rubber hand illusion. The identification of judging and experiencing, along with the fact that only one content (one of the multiple drafts) can win the competitive process and be conscious creates a problem for explaining how, during the rubber hand illusion, that subjects can feel the rubber hand is their own and simultaneously judge that it is not.

As a result I offer a hybrid account. I suggest a quality space account explains the phenomenal qualities of the feeling of embodiment and avoids problems of identifying judging and feeling. Phenomenal qualities are not all there is to consciousness, however, and so I offer a Dennettian competitive processing account to explain the subjects’ awareness of those properties, to accommodate confabulations and to explain why sometimes confabulations cannot be distinguished from veridical reports. By splitting our account into a quality space account of phenomenal qualities and a competitive processing account of awareness we gain the strengths of both and avoid the weaknesses of each.

Having shown in previous chapters how to study the phenomenal qualities of the feeling of embodiment using quality spaces and associated techniques, I elaborate in the next chapter how to study awareness via competitive processes. This is done in the process of defending Dennett’s account of awareness from Irvine’s (2012, 2017) objection that “consciousness” is not a scientifically respectable kind.

6.2 Variation in Somatoparaphrenia and Anosognosia

6.2.1 Somatoparaphrenia

Somatoparaphrenia is the delusional attribution of one of one’s own limbs to another person. There is considerable variation in how this delusion presents, particularly in regards to how patients seem to experience the limb they deny ownership of. In attempting to explain this variation we may wonder if the variation in reports is due to differences in experience, or due to differences in the stories patients tell to make sense of their situation. Before getting to that question, we will need to understand a bit about how patient’s reports differ.

As you will have picked up, there is variation in who the limb is attributed to. As discussed earlier, attributions of the limb to someone else in the room, e.g. the examining doctor, are common. Also common are attributions to close family members, even when they are not present. Other attributions seem more bizarre, such as to an unidentified little girl (Joseph, 1986, p. 510).

This variation could be due to variance in patients’ experience. Patients may experience the limb with an identity, i.e. experience the limb qua the doctor’s or qua their daughter’s (á là the elaborate phenomenology hypothesis). At the other extreme they may simply experience the arm as foreign, i.e. simply lack a feeling of embodiment for it. If such a view is correct then the act of attribution itself if a confabulation, done by the patient to make sense of the confusing set of facts they are presented with. Namely, that the arm doesn’t appear to be their own, yet they are being asked about its identity and it must be someone’s. On this hypothesis, all of the variance in attribution is variance in confabulation (á là the core phenomenology plus confabulation hypothesis).

As well as variance in attribution of the limb, the reports of patients suffering from somatoparaphrenia also vary in the presence or absence of descriptions of supernumerary limbs. Commonly when asked where their real limb is patients suffering from somatoparaphrenia will make vague gestures, or give noncommittal responses (Bisiach, Rusconi, & Valler, 1991; Joseph, 1986), indicating that they do not have a distinct experience of another limb. In contrast, other patients report supernumerary limbs (Brock & Merwarth, 1957). In cases where somatoparaphrenia is associated with anosognosia for hemiplegia patients may report feeling their limb move when they attempt, but fail, to move (Feinberg, Roane, & Ali, 2000). There is the possibility of explaining this variation in terms of variation in experience and of variation in confabulation. Perhaps some patients hallucinate a supernumerary limb, perhaps one that is moveable, and others do not (á là the elaborate phenomenology hypothesis). Alternatively, they may confabulate the presence of another limb based on their knowledge that they have two arms and two legs, but only being able to visually identify one arm or one leg (á là the core phenomenology plus confabulation hypothesis).

When patients are challenged about the identity of the limb they deny ownership of, they provide what look like straightforward provoked confabulations to justify their denial. For example:

Ex.:

Whose arm is this?

A.R.:

It’s not mine.

Ex.:

Whose is it?

A.R.:

It’s my mother’s.

Ex.:

How on earth [sic] does it happen to be here?

A.R.:

I don’t know I found it in my bed.

Ex.:

How long has it been there?

A.R.:

Since the first day. Feel, it’s warmer than mine. The other day too, when the weather was colder, it was warmer than mine. (Bisiach et al., 1991, p. 1030)

Here the patient seems to be confabulating about the temperature of the arm in an attempt to justify her denial of ownership to the examining doctor. Yet even these reports may turn out to be grounded in experience. Why? Because, patients also spontaneously make such comments about the properties of the denied limb, for example:

On or about Sept. 25, his left arm began to feel very cold, and his wife noted that he seemed to regard the left upper limb in a peculiar, furtive manner. Under questioning by Dr. Merwarth, he admitted that he thought it belonged to someone else, more especially his daughter. (Brock & Merwarth, 1957, p. 368)

Do patients experience the denied limb as having these properties (á là the elaborate phenomenology hypothesis), or are they mere confabulations (á là the core phenomenology plus confabulation hypothesis)? What about those who don’t make such reports?

6.2.2 Anosognosia for Hemiplegia

Patients suffering anosognosia for hemiplegia, both with and without somatoparaphrenia, seem to confabulate when asked to move their paralysed limb. Two forms of apparent confabulation are of interest here. First, patients may attempt to explain away their failures to move, commonly with reference to things like soreness or stiffness in the limb (Joseph, 1986, p. 509). These seem most clearly to be confabulations. For example, when asked about her inability to walk, Besharati and colleagues’ patient ED said things such as:

“I can get out of this bed, but they put bars on to stop me” or “Yes I can walk, if they let me go out, I could walk” or “There is nothing wrong with my body, it’s the chair”. (Besharati, Kopelman, Avesani, Moro, & Fotopoulou, 2015, p. 334)

Second patients may claim to have actually moved. Consider, for example, this discussion between an examiner and Berti and colleagues’ patient CC:

E:

(the examiner put her right index finger in in CC’s right visual field) Can you touch my finger with your left hand? (CC does not move)

E:

What happens?

P:

It happens that I am very good.

E:

Have you touched my finger?

P:

Yes . (Berti, Ladavas, Stracciari, Giannarelli, & Ossola, 1998, p. 28)

Some patients make both kinds of responses (Berti et al., 1998, p. 29).

As above, it is not always clear what in the patient’s report is confabulated, and what is a veridical report of their experience. This is especially true of the second type of response, i.e. claims to have moved. As above it is possible that at least some patients hallucinate a moving supernumerary limb. Consider, for example, this striking report from Chatterjee and Mennemeier’s patient EM, who was coming to recognise his paralysis after a period of anosognosia:

E:

How much strength do you have on your left side at this point?

EM:

Below normal. I’d say 40% or less.

E (later):

Can you raise both arms? (Only lifts the right.) Can you raise the left one?

EM:

It feels like it’s rising, but, it’s not.

E:

You thought you had about 40% strength in your left arm. Do you think that’s accurate?

EM:

No, less than 40%.

E:

What percent would you rate it at the moment?

EM:

Right at the moment only 10%. Less than 10% . (Chatterjee & Mennemeier, 1996, p. 229)

This report is almost perfectly ambiguous between being a confabulation and being an accurate report. EM could be hallucinating a supernumerary limb which he feels is moving whilst his paralysed left arm remains unmoved (á là the elaborate phenomenology hypothesis). Alternatively he could be confabulating, e.g. telling a story to make sense of the conflict between his observation that he can’t move, and his feeling that he is able to move (á là core phenomenology plus confabulation hypothesis).

Ultimately in explaining both somatoparaphrenia and anosognosia we will need to explain variance in patient’s reports. Why do some patients suffering somatoparaphrenia attribute their limb to the doctor whereas others attribute it to a close family member? Why do some report supernumerary limbs and others do not? Why do some make reports about the apparent temperature of the limb and others do not? With regards to anosognosia, why do some patients attribute failures to move to things such as soreness or stiffness, whereas others, claim to have moved? Is the experience of patients differing here, or are they producing different confabulations?

From the outset it is difficult to see how we can know what is a veridical report and what is a confabulation. At the very least we must be open to the possibility that at least some of the variation in patient’s reports is due to confabulation. As such, our theory of consciousness must be able to accommodate the existence of confabulations. This is a problem for the conceptual/quality space account of the feeling of embodiment offered so far. Indeed, in the next section I argue that this is a problem for the family of hypotheses (known as ‘vehicle theories’) to which this account belongs.

6.3 Vehicle Theories of Consciousness

Recall, that a vehicle theory of consciousness is one on which consciousness is identified with a particular medium of representation. The term was coined by O’Brien and Opie (1997), but vehicle theories has been offered previously by Clark (1993), Lloyd (1992), and Mangan (1993, 1998). As discussed in the last chapter, vehicle theories are distinctive in that they identify consciousness with a type of mental representation, rather than something done with (some processing of) those representations.

Vehicle theories, thus, explain the difference between conscious and unconscious mental states as a difference in the medium of representation. For example, O’Brien and Opie hypothesise that conscious mental states are ‘explicit ’ mental representations and unconscious mental states are ‘inexplicit ’ representations. By this they mean something quite specific, explicit representations are those for which every represented object is represented by a distinct representing vehicle. In contrast, inexplicit representations are dispositions to elicit particular representing vehicles or are “embodied in the devices primitive operations” (O’Brien & Opie, 1997, p. 276). O’Brien and Opie further analyse this distinction in terms of the features of connectionist networks. They take it that representing vehicles constituted by stable patterns of activity across a layer of units are an example of explicit representations, whereas those constituted by patterns of connection weights are an example of inexplicit representations (O’Brien & Opie, 1997, pp. 279–280; 1999, pp. 955–956). Applying this analysis to biological minds we end up with the position that explicit representations, and thus conscious representations, are constituted by stable patterns of activity across layers of neurons. Whereas, inexplicit representations are stored as sets of synaptic connections which predispose neural networks to produce such patterns of activity.

Vehicle theories in general need not be committed to O’Brien and Opie’s specific hypothesis that consciousness is stable patterns of activity across layers of neurons. They may not even be right that it is explicitness that distinguishes conscious from unconscious representations. It may be, as argued in the forgoing chapters, that it is falling within a particular quality space that makes a mental state conscious. Quality space accounts of consciousness are vehicle theories because they identify consciousness with a specific medium of mental representation. That is, with quality space representations. What matters for the argument here is that vehicle theories identify consciousness with a medium of representation, rather than some processing of those representations. On such a view, how might we distinguish confabulation and veridical reports of experience in somatoparaphrenia and anosognosia?

Generally speaking if some form of vehicle theory is correct, then it should be possible to distinguish veridical reports from confabulations. If consciousness is a particular medium of representation, then identifying everything represented in that medium will tell us what a subject is conscious of. If, for example, a supernummerary limb is represented in the right medium then a patient is conscious of it, if it is represented in some other medium then it is confabulated. In principle, to determine if a particular content is experienced we test to see if it is represented in the right way (say by performing multidimensional scaling analysis of judgements of similarity). Different vehicle theories will have different criteria for distinguishing conscious and unconscious representations, but however this is cashed out, in quality spaces or otherwise, the difference should be empirically detectable.

As I have argued in Carruthers (2018), a major stumbling block for vehicle theories here is in the specification of confabulations. What kind of mental representations are confabulations? I am not here merely talking of the confabulation report which I focused on above, i.e. the words that come out of the subject’s mouth, but rather about the mental state that causes such a report. Such a mental state is, by definition, not conscious, but neither is it a typical unconscious mental state, because it is reported as though it were conscious. How can this possibility be understood? One suggestion is to consider causal relationships. A possibility is that confabulation reports are reports which are not caused by the right sort of mental representation. They are caused by mental representations, of course, but they are not caused by representations in the consciousness medium. The question is what are these mental states and how are they different from conscious and unconscious mental states? They are different from conscious mental states in that they do not involve representations in the right medium, but how can they be distinguished from other unconscious mental states? Unlike other unconscious mental states, they seem to cause reports which treat them as if they were representations in the consciousness medium. This would be a proposal that is hard to investigate empirically, but more importantly for our purposes, it is not a vehicle theory proposal. Vehicle theories distinguish the media of representation by the intrinsic properties of representing vehicles (O’Brien & Opie, 1997, 1999), yet here confabulations are being distinguished from other mental states not only by their intrinsic properties, but also by relational properties i.e. the reports they cause.

It is not clear then that it is possible to accommodate confabulations on a pure vehicle theory. Confabulations, in the sense of mental representations which produce confabulatory reports, cannot be distinguished from other unconscious representations except by reference to relational properties. They are not distinguishable in terms consistent with a pure vehicle theory of the difference between conscious and unconscious mental states. On a pure vehicle theory, then, it is not clear how the possibility of confabulations can be accommodated. If there are confabulations then, it seems that a quality space account of consciousness, as a vehicle theory , at the very least cannot be the whole explanation of consciousness.

Next, I will consider how a functionalist theory of consciousness could account for confabulations and the variation we see in reports from patients suffering somatoparaphrenia and anosognosia. I argue that there seems to be a range of possible accounts of this variation. Whilst one extreme of this range is consistent with vehicle theories (the elaborate phenomenology hypothesis), according to a functionalist approach these options are not really distinct. The functionalist thus predicts the state of affairs we find ourselves faced with, namely that we cannot tell what reports are veridical and which are the result of confabulations. Following this I argue that because a pure functionalist account faces conceptual and empirical problems of its own we need a hybrid account of consciousness that combines vehicle and functionalist consideration to explain different aspects of consciousness. First, let’s have a closer look at how we should interpret reports from patients about their experiences.

6.4 Hetereophenomenology

Hetereophenomenology is a ‘method’ for studying consciousness. I put ‘method’ in scare quotes as, strictly speaking, it covers a variety of methods. For example, the questionnaire reports and extended narratives describing experiences both fall under the rubric of heterophenomenology, as do button presses when used to indicate the occurrence of some experience (Dennett, 1991, pp. 73–74).

Hetereophenomenology is then a set of methods for studying consciousness, specifically for determining what a subject experiences at a particular time. It is intended to help us move beyond older approaches to determining what is experienced in which a single subject, often a philosopher of some note, invites his[1] readers to reflect on an experience and agree with the authors characterisation of that experience. This approach, called the first person plural by Dennett (1991, pp. 66–67), is notable for its failure to find consistent agreement on what is experienced (Hohwy, 2011; Schwitzgebel, 2011). Despite this it still has some currency in contemporary philosophy as a manner for guiding intuitions about experience, usually with reference to red patches on walls or speckled hens, examples that have always been tricky for me, as I do not think I have ever seen either a red patch on a wall nor a speckled hen.

Various methods which fall under the heading of heterophenomenology typically aim to break away from the failures of the first-person plural by using inducible and replicable experiences and standardising how they are discussed. This isn’t always possible; as we will see below it is the inconsistency in reports of those suffering from somatoparaphrenia and anosognosia which gives rise to some important implications for consciousness.

Okay, but what do we actually do in taking a heterophenomenological approach? As we have been doing so far, we treat reports, be they button presses, questionnaire answers or longer narratives, as operationalisations of consciousness. These are our measure of what a subject experiences. For example, if a subject answers with a score closer to 7 on a 7 point scale the questions (i) ‘It seemed as if I were feeling the touch of the paintbrush in the location where I saw the rubber hand’; (ii) ‘It seemed as though the touch I felt was caused by the paintbrush touching the rubber hand’; and (iii) ‘I felt as if the rubber hand were my hand’, following synchronous than asynchronous stroking, then we have good evidence that they experienced the rubber hand illusion (Botvinick & Cohen, 1998, p. 756).

Treating reports as such is no straightforward task as the reports themselves need to be interpreted by the experimenters (Dennett, 1991, p. 75). More problematic is that the reports are themselves interpretations of experience imposed by the subject. As we know, subjects’ reports may be biased by numerous factors, such as an attempt to be helpful, thus indicating the presence of an experience only because that is taken to be helpful for the experimenter (Dennett, 1991, p. 77). In the case of questionnaire reports this can be controlled by adding items regarding experiences which are not expected to be present and then looking for the difference between these reports and the target questions (e.g. Ehrsson et al., 2008, p. 3446).

It is not always so straightforward to control for bias and other interference in reports. When investigating somatoparaphrenia and anosognosia for hemiplegia how can we distinguish between what the subject experiences and what they add as a theoretical interpretation—sense making—of their experience? This is not controllable as it is for the rubber hand illusion questionnaire. In dealing with real world reports we have no control over what experience ought to be present, especially when the reports we are interested in describe experiences which are of private objects, namely the subjects own body ‘from the inside’, rather than public objects (like stimuli presented on the screen which could be experienced by an indefinite number of subjects). This then is one place where heterophenomenology requires a degree of neutrality (Dennett, 1991, p. 95). At the outset, we must remain neutral as to whether or not some feature of a report accurately describes an experience or if it is part of a theory based interpretation of that experience. Whilst allowing subjects complete authority over their reports (Dennett, 1991, p. 96), we must also allow that reports reflect varying degrees of insight into what is going on in the subjects’ own minds (Dennett, 1991, pp. 92–93), including what is experienced (Schwitzgebel, 2007, p. 109).

In taking a heterophenomenological approach to somatoparaphrenia and anosognosia we treat reports (usually narrative reports) as the operationalisation of the experience. Care must be extended to remain neutral regarding the veridicality of the reports. We must remain open to the possibility that reports are not just reports of the experiences had by the patients, but also include some theory-based attempts to make sense of the experience, i.e. confabulations. This neutrality suggests two apparently different understandings of the variation in reports from patients which I will introduce below.

6.5 Two Heterophenomenological Interpretations of Patient Experiences: Phenomenology and Errors of Translation

6.5.1 Option 1: Core Phenomenology and Confabulation

What follows is a story about consciousness that allows us to make sense of the variation in reports of patients suffering somatoparaphrenia and anosognosia. In order to be transformed from an experience itself (which we can’t access in the 3rd person) to a report of an experience (which we can, and which constitute the basic data of a science of consciousness) (Dennett, 1991, pp. 70–72) i.e. for us to operationalise consciousness, a process of interpretation must take place. This isn’t profound; in transforming some information from one representational medium to another an interpretive process is always needed. As in any transformation, the transformation of information about the self or world from the medium of experience to the medium of language may involve some data loss, or it may result in what we might loosely call “errors” being built into the new medium by misinterpretation. Because of the processes of interpretation, in forming a report describing an experience (or more commonly the world as it seemed to be experienced) a single report should never be taken as more than a hypothesis from the subject regarding what they experienced.

Despite this uncertainty, we shouldn’t treat subject’s reports as intrinsically untrustworthy. Rather, as Dennett suggests, we treat the subject as absolutely authoritative regarding their own hypothesis about their own experience

(Dennett, 1991, p. 96)—allowing us to continue to use heterophenomenology as we have so far. Further, we can attempt a science of experience types. Again this is just a description of what we have been doing so far. Of course, because of the unfortunate nature of—real or apparent—temporal dynamics we can never return to a particular experience. Even if we did, our interference would change the experience. What we can do, however, is what we have been doing. Record experiences with enough common features for them to be considered a type. This is what we have been doing with both somatoparaphrenia and anosognosia. Once classified, we can ask about what features instances of the type seem to have in common. These common experiences then constitute our first formulation of the phenomena to be explained.

Taking somatoparaphrenia for example, we see several themes which reports cluster around. The first of these is the denial of ownership of a limb, seeming to reflect a loss in the feeling of embodiment. This I will call the core content of somatoparaphrenia. I argued in Chapter 2 for that this is not merely a confabulation produced by sufferers of anosognosia for hemiplegia in response to their inability to move. This feature defines somatoparaphrenia, but does not exhaust patient reports. As above, patients also tend to attribute their arm to a particular individual. Commonly (but not exclusively) these attributions cluster into two types . Those being attributions to someone in the room with the patient, e.g. a doctor, or to someone who is not present, often a close family member. Reports from patients suffering from somatoparaphrenia also vary as to the presence or not of supernumerary limbs and illusory movements. Additionally, patients may or may not report the perception of properties of the target limb which seem to distinguish it from their own, properties such as apparent temperature. These types of variance constitute what I call the “elaborate content” of somatoparaphrenia.

If we take anosognosia for hemiplegia as an example, we also see reports tending to cluster into types . As is defining of the condition all patients report being able to move normally, even though they cannot. This is the core content of anosognosia. However, we have seen variance in patients reports with regards to the presence or absence of supernumerary limbs and in attempts to explain away failures to move. This I will call, in line with the above, the elaborate content of anosognosia.

Here are what we might think, given the current state of evidence, constitute the experience to be typed and explained under the headings of ‘somatoparaphrenia’ and ‘anosognosia for hemiplegia’. But, how are we to tell what in patients’ reports is veridical and what is confabulated? Put another way: do we explain the various types of somatoparaphrenia and anosognosia in terms of differences in experience or of differences in the stories told to make sense of those experiences? This problem stands out more in these (and similar) cases, because the experiences of these patients are not shared or shareable by everyone. As such, there is no shared vocabulary for describing the experience. A prediction of this assumption is that the more commonly a type of experience is shared the fewer of these errors will be observed, e.g. dreams, hallucinations and hypnotically induced experiences should contain many such errors, whereas reports of visual scenes, music recordings or the intentions behind another’s action should contain fewer errors or confabulations because these are shared experiences.

Here is where we return to the distinction between core and elaborated content. From our attempts to type experience, we see the best evidence that it is the core phenomenology which is experienced. Other aspects of the reports seem more questionable, or more likely to be confabulations. This sets our first hypothesis: The subject only experiences the core phenomenology (either the loss of a feeling of embodiment, or a preserved capacity to move) and all other apparent experiences reported in the narratives are not experiences but confabulations applied by the subject in an attempt to make sense of the core phenomenology, and observed conflicts between that phenomenology and the testimony or evidence of others, for themselves and for others.

When confronted with a subject suffering somatoparaphrenia, anosognosia or both who reports supernumerary limb movements, for example, an advocate of this hypothesis should say that they are wrong and had no such experience. Instead they should hypothesise that the experience of a supernumerary limb is the best way available to the subject to make sense of what she actually did experience (e.g., an unmoving arm that should be moving). This is an extension of all subjects’ occasional (but controllable) tendency to report what should have plausibly been in their experience given what else they know, rather than what was actually experienced (Schwitzgebel, 2008).

6.5.2 Option 2: Elaborate Phenomenology

The above cannot be true if a quality space account is a complete account of consciousness. As a vehicle theory, quality space accounts are unable to accommodate confabulations. So, it is a good thing that this is by no means the only interpretation available to us in attempting to understand the variation seen in reports of patients suffering somatoparaphrenia and anosognosia. We might hypothesise that there is significant variation in the experiences of different patients and that these differences are accurately reported by them. Sure, the core phenomenology is shared by all patients and some other aspects, like supernumerary limbs are not, but the fact that these features are not shared by all does not mean that they are not shared by some. On this option we could take the clustering of patients into subtypes around the presence of features such as supernumerary limbs more seriously than we did for the first hypothesis. Under this second hypothesis, there are different types of somatoparaphrenia and anosognosia (with and without hallucinated supernumerary limbs, for example), which involve different clusters of experience and need somewhat different explanations.

6.6 Can We Distinguish These Interpretations?

We have two, apparently competing, hypotheses regarding the nature of the experiences of patients suffering from somatoparaphrenia and anosognosia. In order to account for the core content of the experience, the elaborated content and the high degree of individual difference in that content, these two apparently different options are available:

1. 1.

Patients only experience the core content and then confabulate a story in attempt to make sense of this bizarre experience. Call this the core phenomenology plus confabulation hypothesis.

2. 2.

Each patient has a different experience and that errors are not (or not necessarily) introduced in reporting that experience. Call this the elaborate phenomenology hypothesis.

According to a quality space account we need to know if the elaborate content is represented in a quality space or not. If so then it is conscious, if not then a pure quality space account is in trouble. Similarly, an advocate of a different type of vehicle theory would ask if it is represented in the conscious medium (e.g., explicitly), or not. However, even if such evidence were obtained it would not convince an advocate of explaining the variation in reports in terms of confabulation.

To see why, let’s consider an extreme thought experiment. I emphasise that this thought experiment is not an argument for interpreting variation in reports as confabulations or not. Rather it is meant merely as an illustration of how different interpretations of even idealised data must be interpreted differently depending on one’s preferred account of consciousness, and so don’t provide evidence for one interpretation over the other. Regardless of what we discover about the medium of mental representation of things like supernumerary limbs this won’t help us decide if those limbs are confabulated or hallucinated unless we have prior reason to accept a vehicle theory as a complete account of consciousness.

Let us step away from the facts and into the realm of imagining future discoveries. Perhaps some super high-resolution (in time and space) brain scanner could distinguish these accounts by identifying exactly the kind of representing vehicle carrying each content. According to a vehicle theory of consciousness it should be possible, in principle, to make such a discovery and for this to tell us what is represented in the consciousness medium and what is merely represented unconsciously.

A functionalist approach to consciousness requires a different interpretation of the imagined facts about what is observed in a super brain scanner. Whilst the vehicle theorist would interpret such information in light of the elaborate phenomenology hypothesis, the functionalist would see such evidence as unable to distinguish the elaborate phenomenology hypothesis and the core content plus confabulation hypothesis, because if functionalism is right, these hypotheses are not really distinct.

To see why, consider what it is that our two hypotheses agree on. Both take it that there is some representation of the core phenomenology (that is being able to move or that the limb is not one’s own). This content common to each patient’s reports, as so is presumably common to their experiences. But, subjects report more than this (e.g., supernumerary limbs). Are these elaborations a part of the experience, or just what subjects say about the experience. What could a futuristic brain scanner tell us about this? Suppose we could use it to identify a particular pattern of activity that is a vehicle representing, e.g. the limb as not the patient’s own. On the account offered in previous chapters this would be an on-line representation of the limb not matching an off-line prototype. It could also identify patterns of activity that are vehicles with the content of the elaborations should they occur. Now, when the first of these vehicles, the one that represents the core content, occurs this is the earliest possible time at which the subject could experience the core phenomenology (Dennett, 1991, p. 124). But, unless we are to arbitrarily declare that such a representation can never occur unconsciously, a functionalist would argue, there is no reason to think that the tokening of this vehicle as observed by our super scanner constitutes the subject becoming aware of the core phenomenology . In other words, this is only evidence that this content is conscious if we assume that a vehicle theory (such as the quality space account) is a complete account of consciousness. Advocates of a functionalist account, for example, would see this as evidence that such content is represented and not about consciousness of that content at all.

Consider then something of the elaborate content, say a supernumerary limb. If our super brain scanner shows that a supernumerary limb is represented in the right medium (e.g., in a quality space) then this is evidence that the limb is hallucinated, but, again, only if we assume a vehicle theory as a complete account of consciousness. An advocate of functionalism would, instead, interpret this as evidence that the limb is represented, but claim that this can’t tell us if it is confabulated or hallucinated because it doesn’t tell us about how that content is experienced (as done by Cohen & Dennett, 2011, for example). The same would certainly hold for any behavioural evidence obtainable about whether or not the supernumerary limb is represented in a conceptual space or not.

For the functionalist there is no evidence which could tell us whether our patients experience only the core phenomenology and then confabulate in an attempted to make sense of this odd experience or if they have quite distinct and elaborate phenomenology.

As Dennett (1991, 1995) has argued, functionalism collapses the apparent distinction between adding content to an experience and merely adding it to judgements about the experience. On such a view, whilst mental representations are distinct entities that should be identifiable in brain activity, consciousness of that content is just a way or set of ways of using of the content in the broader cognitive system. Functionalist accounts will differ in precisely which uses of the content constitute consciousness and we can leave the specifics of such use for empirical discovery (although I will say more on this in the next chapter), but we might think that relevant uses will be reporting, otherwise acting on and remembering the content. If this is true then use of a content constitutes being conscious of it, and confabulations, like judgements, are uses of mental representations.

For possible confabulations our question is this: does the elaboration of the core content of somatoparaphrenia or anosognosia become elaborated (i) before the content is experienced, thus meaning subjects experience elaborate phenomenology or (ii) after the content is experienced by a process of confabulation? On a functionalist account of consciousness these are not distinct options. The elaborative/constructive/confabulative processes are part of the use of the core content. As such they partially constitute consciousness of that content. It makes no sense to ask if these processes take place before or after consciousness of the core content because they are consciousness of the core content. If this is correct, then the core phenomenology plus confabulation hypothesis and the elaborate phenomenology hypothesis are not distinct options at all; they are different ways of saying that the core content is elaborated during processes which constitute being conscious of it. It follows that because these are not distinct options, we would expect that they would not be distinguishable empirically, which is consistent with the available evidence, and, as we have seen, a plausible interpretation of this kind can be offered for imagined idealised future discoveries, regardless of what they are.

For a vehicle theory to be true, it must be possible to obtain evidence for the elaborate phenomenology hypothesis over the core phenomenology plus confabulation hypothesis, because such accounts do not allow for confabulations. However, it seems that there is no evidence which could exist which would show this without first assuming a vehicle theory. Although it is possible for a vehicle theorist to explain away apparent confabulations in anosognosia and somatoparaphrenia, thus making the account possible, there is no evidence which can show that this is the right approach. In contrast, functionalist accounts, broadly speaking, seem to predict the difficulties in empirically distinguishing the core content plus confabulation hypothesis from the elaborate phenomenology hypothesis. For a functionalist these are not truly distinct options. Perhaps them we should consider a pure functionalist theory of consciousness?

6.7 The Identification of Judging and Experiencing as an Objection to Functionalism

Several objections have been raised to pure functionalist accounts of consciousness which suggest that they cannot be complete accounts of consciousness. These objections often focus on an implication or prediction of the functionalist account which are either empirically or conceptually questionable. Tye (1993) finds the functionalist elimination of something seeming a certain way to a subject in favour of the subject judging that things seems a certain way to them problematic. The Functionalist does indeed make this elimination,[2] as the judgement is a kind of use of a mental content, specifically tied to report, which thus partially constitutes an experience of that content. Tye finds this elimination unpalatable as it would seem to suggest that a subject can never be wrong about how things seem to them (Tye, 1993, p. 896). This sits in tension with the heterophenomenological approach discussed above (Schwitzgebel, 2007, p. 111), on which reports can at best be taken as hypotheses about what the subject is experiencing, thus leaving room for the possibility that the subject may be mistaken about their experiences. Using heterophenomenology we wanted to allow that subjects sometimes report sincere theory-based beliefs about what they experience, which are, never-the-less, wrong. Yet if judging that an experience is a certain way is constitutive of having that experience then it cannot be the case that the subject is in error about their experience, they necessarily experience what they judge themselves to be experiencing.

How might the functionalist resolve this tension? Can functionalism be modified? Or perhaps because such judgements are only one of the uses to which a mental content can be put, we can create room for error by pointing out the judgements are only partially constitutive of experiencing that content. Perhaps we could reinterpret these findings, suppose our errors are always in our theories of what our experiences should be, rather than in judging what our (occurrent) experiences are (Dennett, 2007, p. 263)? I do not wish to rule out these as potential strategies, however, the most direct approach to this problem is to consider heterophenomenology itself and the process of translation between a mental representation and a verbal report of that representation.

Dennett (2007, p. 255) creates room for error by suggesting that the conceptual resources we have for reporting experience are too limited to accurately describe experience, we are thus forced to resort to metaphor in making reports. This is analogous, he supposes, to someone who classifies the world into ‘plants’, ‘animals’ and those things which are inanimate and unliving, describing a car as an ‘animal’ (Dennett, 2007, p. 255). Like this fictional character when we introspect our own experiences, we lack the concepts needed to accurately describe our experiences. Dennett teases this out a little by pointing to the difficulty we have in describing the difference between seeing a house and imagining or remembering it (Dennett, 2007, pp. 256–257).

However, there is an important difference between us in relation to our experiences and the person who incorrectly classifies a car as an animal. Our fictional character could get better at describing cars by learning new concepts like MACHINE, WHEEL, ENGINE or 1988 DAIMLER XJ40. We are not in the same position when it comes to experience. When we learn the new concepts that could help us understand the difference between seeing and remembering a house, that doesn’t improve the accuracy of our reports, because introspectively there is nothing for these concepts to refer to. They really do refer, of course, but not to aspects of experience. Rather they refer to unconscious representations and processes.

As such we are necessarily left with potentially inaccurate/metaphorical reports of experience even though judging that something seems a certain way is (partially) constitutive of experiencing them to be that way. It is, recall from the above, the employment of such metaphor that allows us to understand how theory driven claims about what experience ought to be like can end up in reports of what an occurrent experience is like.

As in the discussion of heterophenomenology above, it is the process of translation and interpretation from one medium of representation (non-linguistic) to another (natural language) which creates the problem for the subject in knowing their own experiences. But, this consideration surely points us in another direction. Why isn’t it the case that this first medium of representation (the non-linguistic one) just is experience and the report just a use of that representation? The problem for such a view is to distinguish conscious and unconscious mental representation, but vehicle theories already offer a solution to this. On the account given in previous chapters experienced content is represented in quality spaces and non-experienced (i.e. unconscious) content is represented in a different medium.

This approach seems preferable, as Dennett’s identification of judging and experiencing faces empirical problems. Consider again the rubber hand illusion. During this illusion subjects report that they feel that the rubber hand is their own, and, at the same time they (typically) judge that it is not. For Dennett, then, there are two judgements being made simultaneously by the subject, one that constitutes the feeling of embodiment and another which is the rejection of that feeling as veridical. However, on Dennett’s account the subject is only conscious of the winning judgement. Yet in the case of the rubber hand illusion there seems to be two contradictory winning judgements simultaneously. Both of these guide future reports about and behaviours toward the rubber hand. Some modification, at least, is needed to a Dennettian account, there can be more than one ‘winning’ content at a time, at least in such strange circumstances. But, and here is the rub, why would those two judgements feel so different? The feeling of embodiment feels like a feeling, it is bodily, yet the rejection of this feels different, it feels like declarative memory, like words. On the quality space account in previous chapters this difference in feeling is due to the different natures of the representations. The feeling of embodiment is part of an on-line representation of the body in body space , the judgement that this feeling is non-veridical comes from the story one tells about the situation one is in, and from stored knowledge of facts (e.g. if my hand did get there and look like that, it would have hurt a heck of a lot). Those representations are of different forms and so they feel different. Is there any chance then of having a quality space account which can accommodate the realities of confabulation which we met above?

6.8 Hybrid Accounts of Consciousness

A pure quality space account clearly distinguishes consciousness and report. Consciousness is representation in quality space, whereas report is one use of that content. This seems to be an incomplete account of consciousness as it has difficulty accommodating the possibility of confabulation (because it is a vehicle theory ). Alternatively, pure functionalist accounts which identify consciousness not with the medium of representation, but with how it is used, face conceptual and empirical problems in accounting for facts such as subjects feeling as if a rubber hand is one’s own, whilst simultaneously judging that it is not. Specifically, such an account cannot explain why feeling that it is one’s own and judging that it is not feel so different. If all there is to experience is the use of those contents, i.e. making the judgements, then they shouldn’t feel so different. The difference should be only the difference in content. In contrast, a quality space account can explain why they feel so different. The feeling of embodiment in the limb is explained by the matching of the on-line representation of the limb to the off-line prototype, i.e. as a region of body space . The judgement that it is not one’s own, in contrast, comes from declarative reasoning in a different medium. But, if this is right then we’re back to the worry about confabulation.

The solution to this is just to combine a quality space account with a functionalist account, but to understand them as explaining different aspects of consciousness. As above, quality spaces explain why experiences feel the way they do. In other words, they account for the phenomenal qualities of experience. We can then account for confabulations by supposing that confabulations are a particular use of these representations, not a different kind of representation.

On such a view, are patients conscious of the content of their confabulations? To answer this, we need to understand what it is about consciousness that the use of content explains. The use of content, on this hypothesis, doesn’t explain the phenomenal qualities of experience, but it explains the subject’s awareness of those qualities. We will see more on this distinction in the next chapter. The failure of a purely functionalist account is to explain how two contents being used in the same way (in judgements) feel so different, but if that task is assigned to quality spaces then the functionalist account can still answer the “… and then what happens?” question we met in the last chapter. If awareness then is a matter of the use of content then we gain the strength of a functionalist account in accommodating the possibility of confabulation. A patient is conscious of a confabulated supernumerary limb if that content is used in the right way. What is the difference between a confabulated and hallucinated supernumerary limb? If the limb is represented in the right quality space (body space ) independently of how it is used then it is hallucinated. If it is not represented in that space, but none-the-less appears in the story patients tell to make sense of their experience then it is confabulated. The limb then is conscious in that the patient is aware of it, but it doesn’t have the same phenomenal qualities it would have were it hallucinated (i.e. represented in body space ), even if the subject believes that it does.

6.9 Conclusion

In this chapter, I have considered how we might distinguish veridical reports from confabulations in reports of experience from patients suffering from somatoparaphrenia and anosognosia for hemiplegia. Although each disorder seems to involve a core experience, the elaborate content of patient reports could be due to variation in either experience or confabulation. This creates a problem for a pure quality space account of consciousness, which, as a vehicle theory , has difficulty accommodating the possibility of confabulations. The alternative is a Dennettian functionalist account of consciousness. Yet this account faces conceptual and empirical problems. I suggested that the solution to this is to distinguish explanations of phenomenal qualities from explanations of those qualities which the subject is aware of. I suggest that the quality space account, as a vehicle theory , is a successful explanation of the phenomenology of the feeling of embodiment, however, that a functionalist account is needed to explain awareness of those properties. This avoids the problems of a purely functionalist or vehicle account. The quality space account only needs to target phenomenal qualities regardless of what is reported, and so its inability to accommodate confabulation doesn’t matter. The functionalist account in contrast can explain what is reported, whilst remaining neutral as to what phenomenal qualities are really present. I close by considering, in a roundabout way, how to develop a functionalist account of awareness and defend it from a recent objection.

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Footnotes

1

Strikingly commonly ‘his’.

2

Although we may be tempted to ask whether this move is best understood as identification or reduction rather than elimination it makes little difference to the argument in this section. Here I use “elimination” as it fits better with Dennett’s proposal that there are no “real seemings” independent of judgements about seemings. I other contexts it will matter more to clarify the nature of this relationship and functionalists may differ on their views.

© The Author(s) 2019

Glenn CarruthersThe Feeling of Embodimenthttps://doi.org/10.1007/978-3-030-14167-7_7

7. Completing the Hybrid Account: Awareness Is a Functionally Emergent Kind

Glenn Carruthers[1]

(1) School of Psychology, Charles Sturt University, Port Macquarie, NSW, Australia

Glenn Carruthers Email: gcarruthers@csu.edu.au

7.1 Introduction

In the last two chapters I argued that the quality space account of the feeling of embodiment I offered is insufficient to explain the feeling of embodiment. I suggested that this account needed to be augmented with a functionalist account of awareness. Whilst the region of body space in which on-line body representations match the off-line prototype explains the phenomenal qualities of the feeling of embodiment, it is the use of those representations which explains the subject’s awareness of those qualities and allows us to accommodate the possibility of confabulations. Such a hybrid account is challenged by a recent argument offered by Irvine to the effect that this concept of AWARENESS is not a scientifically respectable kind. In this chapter I defend functionalist accounts of awareness from her arguments and, in doing so, explore how to study awareness further.

Irvine (2012a, 2017) has argued that our concept of CONSCIOUSNESS does not refer to a scientifically respectable kind, in that it refers to an arbitrary grouping of cognitive processes and so should be eliminated from scientific practice in favour of those processes considered in isolation. From the fact that different measures of consciousness can provide contradictory answers to questions of what a subject is conscious of, she concludes that each measure taps a different cognitive process rather than a unified phenomenon of consciousness. Her argument thus targets AWARENESS in particular. I argue, however, that an existent set of explanations of awareness are not threatened by her arguments. These accounts, which I group together as “functional emergence” accounts, interpret the apparent contradictions as artefacts of the artificial categorical nature of the measures used. Measures of consciousness answer the question “did you see it” with a categorical “yes” or “no” and do not allow for cases of indeterminate consciousness . This is true even for some more nuanced measures which allow subjects to respond categorically that they are ‘weakly’ conscious of something. Functional emergence accounts of consciousness, such as that offered by Dennett, however, predict the existence of mental states of which the subject is neither aware nor unaware and that these states will be identified by apparent contradictions in answers to questions like “did you see it?” It seems then, that Irvine’s argument is consistent with the revisions to our concept AWARENESS needed for functional emergence accounts. The upshot of this is that Irvine has failed to make the case the revised concept of AWARENESS actually used in this part of the scientific and philosophical literature (as opposed to a pre-theoretical concept of AWARENESS) should be eliminated.

As the hybrid account offered here makes use of Dennett’s functional emergence account of awareness, it is also protected from Irvine’s argument. Responding to Irvine’s argument also has the added benefit of allowing us to explore how to further study awareness according to the hybrid account.

7.2 What Notion of “Consciousness” Is at Stake?

In order to evaluate her argument for the elimination of ‘consciousness’ we first need to know which of the many notions of consciousness at play in the literature concerns Irvine. We will see here that Irvine’s primary concern is consciousness as awareness or cognitive/behavioural access , á là Block (Block, 1993, 1995, 2007). The notion of ‘consciousness’ Irvine considers rests on how consciousness is purportedly operationalised. The kinds of operationalisations she considers follow the mainstream of cognitive neuroscience and much of philosophy (although arguable not the mainstream of contemporary cognitive psychology). The operationalisations all ask what visual stimuli the subject is aware of, i.e. what do they know is present.

In this way the notion of ‘consciousness’ that matters for Irvine can be probed by asking the question “did you see it?” (Irvine, 2017, p. 101). The focus on visual consciousness per se, is not particularly worrisome. Vision is the sense that has been rigorously tested the longest and so if a respectable notion of consciousness can’t be found there, it likely won’t turn up anywhere. This, we will see, Irvine concludes doesn’t happen on the grounds that questions like “did you see it?” don’t have a single consistent answer (Irvine, 2017, p. 101).

In focusing on these kinds of measures Irvine ignores measures targeted specifically at examining the phenomenal properties of mental states. She does consider some hypotheses on which ‘phenomenal’ and ‘access ’ consciousness refer to different types of consciousness, such as Block’s (1995) introduction of the distinction and Lamme’s (2006) ‘neural stance’ (Irvine, 2012a, pp. 6 and 109). Yet the measures of consciousness considered are almost all different ways of answering the question “did you see it?” The only exception to this being Lamme’s proposal that activity in locally recurrent neural networks be identified with phenomenal consciousness and activity in globally recurrent networks be identified with access consciousness. This view she rightly criticises on the grounds that it is somewhat arbitrary and not (at least not yet) internally consistent (Irvine, 2012a, pp. 109–115). In contrast, approaches such as just noticeable differences, similarity rating scales and odd one out judgements—in short methods that give data which is analysed using multidimensional scaling (Clark, 1993; Gärdenfors, 2000)—are not considered. These methods are designed to provide a set of ordered lists or multidimensional spaces which rank stimuli in terms of their perceived similarity (Clark, 1993) and so provide a detailed description of the phenomenal properties of subjects’ representations of sets of stimuli. As Irvine has chosen not to include a discussion of such methods it is safe to conclude that her interest lies in consciousness qua awareness/access rather than the nature of phenomenal qualities. Indeed other advocates of quality space accounts of phenomenal (or sensory) qualities also take care to distinguish the explanations of phenomenal qualities from the explanation of the subject’s awareness of those properties (e.g. Rosenthal, 1991; Young, 2014; Young, Keller, & Rosenthal, 2014) as I did in the last chapter.

There are a variety of views available in the literature as to the relationship between phenomenal qualities and conscious awareness. It might be (1) that these are different types of consciousness (Block, 1995) or otherwise distinct phenomena (Schier, 2009), (2) that phenomenal qualities can be reduced to awareness (Dennett, 1991) or (3) that they are different properties of the same thing, i.e. that only the mental states which underlie awareness have phenomenal properties. In testing hypotheses of the first type it would be appropriate to consider the multidimensional scaling methods. That Irvine chooses not to again suggests her interest is conscious awareness rather than phenomenal properties.

We see that conscious awareness is the notion of consciousness at stake for Irvine in the theories she chooses to discuss and how she explicates the notion of consciousness which is the explanatory target of those theories. According to Irvine on ‘worldly discrimination theories’ a subject is conscious of a stimulus if they are sensitive to it in the right way. Where ‘the right way’ varies by theory but is always operationalised by a behavioural indication that a stimulus is present or not (Irvine, 2012a, p. 6). Similarly, ‘integration theories’ seek to explain consciousness qua global availability of information (Irvine, 2012a, p. 7). Higher order thought theories “are based on the idea that if someone is conscious of something, this means they are aware of a representation of it” (Irvine, 2012a, p. 7) and that some variations require that:

…being conscious of something entails that subjects are able to comment on this state (e.g. by producing confidence judgements about seeing it), or that being conscious of something entails having some disposition or attitude towards it. (Irvine, 2012a, p. 7)

Although these types of theories offer different accounts of what consciousness ultimately is, all are clearly targeted at conscious awareness and not phenomenal properties. This is consistent at least with the view that our concept of consciousness is revisable (Irvine, 2017, p. 97). It also fits with how advocates of such theories describe the target of explanation of their theories. For example, Rosenthal says:

Sensory qualities are just whatever properties sensory states have on the basis of which we distinguish among them and sort them into types. Since state consciousness consists in our being conscious of a mental state in some suitable way, these properties are independent of state consciousness. (Rosenthal, 2002, p. 411)

It is similarly striking that Irvine chooses not to discuss theories which are targeted at explaining such qualities, such as Clark’s (1993) quality space account. Again, this suggests that it is only conscious awareness/access consciousness, not phenomenal qualities, which Irvine is seeking to eliminate.

As such Irvine’s argument does not threaten the quality space account of the phenomenal qualities of the feeling of embodiment offered here. It may, however, threaten the idea that subjects’ awareness of the feeling of embodiment is constituted by some use of an on-line body representation, such as winning a competitive process for cognitive access , á là Dennett. In order for the hybrid account offered here to be successful I need to defend it from Irvine’s argument that AWARENESS is not a scientifically respectable kind. I do so below and in doing so also explore how to further study awareness on this account.

7.3 Irvine’s Argument

In this section I will explicate the core of Irvine’s arguments for the elimination of AWARENESS from the science of the mind. It focuses on a consideration of what is measured by purported operationalisations of awareness. In examining the border between conscious and unconscious perception, typically using masked stimuli, Irvine is lead to conclude that the question “did you see it?” cannot be answered consistently. Depending on the operationalisations used, the answer to this question can be both ‘yes’ and ‘no’ simultaneously. Let us turn to how these apparent inconsistencies arise and their theoretical significance.

Irvine first considers measures of awareness based in verbal report. She notes well established effects of subliminal priming in which a visual stimulus (the prime) is masked to a degree that subjects report that they cannot see it, yet it still effects behaviour. Often dissociations between report and other behaviour are taken as evidence that the prime is perceived unconsciously (Irvine, 2012a, p. 15). Yet this conclusion depends on the assumption that verbal report is a reliable and exclusive measure of the subject’s awareness. Problems with using verbal reports in such a way are well known. In particular there seems to be no way to completely eliminate various biases that cause subjects to report what they think they ought to see, or what they think is helpful for the experimenter, rather than what they actually see (Irvine, 2012a, p. 16; 2012b; see also Schwitzgebel, 2011). That is, reports may be grounded in metacognitive beliefs about, for example, how vision works as much as in occurrent experience, that is to say reports may be confabulations rather than veridical. Irvine offers some useful critiques of attempts to avoid or minimise such biases, which, whilst important, needn’t concern us here. Let us agree with Irvine and the psychological orthodoxy that there is no way to guarantee that all biases can be eliminated from the production of subjective reports of what is seen.

In response to issues of bias the traditional reaction in the study of vision has been to seek more objective indicators of awareness, such as dʹ. This is a measure of a subject’s sensitivity to stimuli. Specifically, a value of dʹ > 0 indicates that a subject is able to discriminate, to some extent, stimuli plus noise from noise only. For example, a subject is presented with a series of stimuli composed of a target plus a mask or just the mask and forced to choose “target present” or “target not present”. A value of dʹ > 0 indicates that they are better than chance at indicating when the target is present (Irvine, 2012a, p. 42). Some biases may lead subjects to say they don’t see some stimuli when they very likely do see it. Irvine’s favourite example of this is that subjects are better at reporting, or otherwise responding to, the word “shot” than “rubbish” under identical masking conditions (Irvine, 2012a, p. 5). A result of dʹ not different to zero, however, indicates that the subject can do no better than chance at discriminating target plus mask from mask only. The conditions under which this occur are stable and not manipulable by manipulating biases or motivation (Irvine, 2017, p. 98). As such dʹ not different from zero is taken as a bias free measure of when a target is not seen (Irvine, 2012a, p. 43).

However, it does not follow from this that a dʹ > 0 indicates that the target is seen (Irvine, 2012a, p. 43). Subjects have been repeatedly shown to report that they do not see targets even when dʹ > 0. This means that subjects will not report the presence of a masked target even when they are better than chance at indicating whether or not the target is present in the forced choice task. Because of this, we might conclude that dʹ is not a measure of awareness, and that instances in which subjects report not seeing targets, but for which dʹ > 0, allow us to investigate purely unconscious processing. But, as Irvine reminds us, this only follows on the assumption that verbal report is an exhaustive and exclusive measure of awareness (Irvine, 2012a, p. 61). Because such reports are biased by factors other than experience, we are not entitled to this assumption (Irvine, 2012a, p. 44). Alternatively, we may suggest that dʹ is a better measure of awareness. After all the higher the value of dʹ the more confident subjects are that they have given correct answers to test questions, including, but not limited to, inhibiting the target word in stem completion tasks (Irvine, 2012a, p. 44). But, this only works on the assumption that verbal report is irrelevant to consciousness (Irvine, 2012a, p. 45) and that subjects can’t form confidence judgements about unconscious processes (Irvine, 2012a, p. 46).

Now we are in a position to see the heart of Irvine’s argument. When we look at cases such as masking of stimuli the answer given to the question “did you see it?” depends on the measure used. These measures can give contradictory answers. For example, subjects may report not seeing targets that they are nonetheless able to discriminate. There are no non-arbitrary grounds for preferring one measure over another and all measures have inadequacies like those considered above (Irvine, 2012a, p. 48). Reportability, discrimination, inhibition of a prime in answering a question and confidence judgements all could be used to index the presence of consciously seeing something, but all dissociate (Irvine, 2012a, pp. 44–48, 61). Because of the observed dissociations, we have good reason to suppose that all these measures operationalise somewhat different phenomena and that calling these all different types of awareness is arbitrary (Irvine, 2012a, p. 62). For these reasons, Irvine concludes that awareness is not a viable target of scientific study, but that there are a variety of different cognitive processes which make use of representations of visual input that can be studied. We should, thus, eliminate the concept

AWARENESS from the scientific study of the mind.

Irvine offers a variety of arguments that because of the problems identified above (and stated at premise 1) that we cannot do a science of awareness. The most powerful of these arguments fall into two classes: (A) that awareness cannot be adequately distinguished from unconscious processing and (B) that there is a lack of converging evidence for what a subject is aware of. Let me consider an example of each kind of argument.

One example of an argument of type A, that awareness cannot be adequately distinguished from unconscious processing, focuses on dissociation methods in cognitive science. It is common in cognitive science to identify different explanatory targets and potential cognitive mechanisms via dissociations. For example, the double dissociation between apraxia (a disorder of skilled movement caused by central nervous system damage) and autotopagnosia (an inability to localise body parts) has been used to argue that there are different mechanisms for moving and for identifying one’s own body (de Vignemont, 2010). But, because of the kinds of contradictory results seen above we cannot use dissociations to adequately distinguish what the subject is aware of, from what is processed outside of awareness (Irvine, 2012a, p. 155).

For Irvine, this problem arises not just because different purported operationalisations of awareness seem to contradict each other, but because any decision we make about which measure to prefer is arbitrary. Consider again a case in which a subject is attempting to detect the presence of a particular stimulus in a noisy display. Those cases where the subject shows a dʹ of greater than zero, but is unable to verbally report the presence of the target, might be interpreted as showing a dissociation between unconscious processing which can influence behaviour and awareness of the target which is shown by verbal report. But, as we saw above, prioritising verbal report as a measure of awareness seems arbitrary and problematic. Alternatively, we might think that these cases don’t show a dissociation between awareness and processing outside of awareness because dʹ is a good bias free measure of what the subject is aware of. This, however, seems arbitrary (why wouldn’t task demands change what a subject is conscious of?) and potentially undesirable (pre-theoretically) because it means that subjects can be aware of stimuli which they can’t report.

For Irvine, any attempt to map awareness and processing outside of awareness onto dissociations such as these is arbitrary, and thus existent attempts to do so lack the signs of good scientific practice (Irvine, 2012a, pp. 63–66). Instead she proposes that they be understood as showing dissociations between different cognitive processes, such as the capacity for discrimination and the capacity for report, and that we leave AWARENESS out of it.

Similarly, for Irvine problems such as this undermine attempts to find converging evidence for what subjects are aware. This is the type B argument introduced above. Importantly for Irvine it means that we cannot integrate findings about awareness across disciplines or, perhaps even between individual researchers (Irvine, 2012a, p. 156). The reason for this is straight forward enough, if it is not clear that different researchers are studying the same phenomenon then any attempt to integrate their findings will be arbitrary.

So far, I have attempted to understand the core of Irvine’s argument for the elimination of AWARENESS from inconsistencies in measures of awareness and introduced the problems that this creates for a science of consciousness. Irvine (2012a) considers many other examples of such purported inconsistencies in Chapters 2–5 (with the remaining arguments depending on the conclusions reached in those chapters, or other similar dissociations), considering a small number of these cases is enough, for the purposes of this chapter, to show how the concept of AWARENESS as used in functional emergence accounts is not threatened. On these hypotheses the apparent contradictions in measures of awareness are predicted because such accounts ought to be understood as requiring that there are states which are indeterminate as to awareness, i.e. mental states of which the subject is neither aware nor unaware. Following this I will discuss how there can be a science of awareness on a functional emergence view. This serves a secondary purpose of exploring how awareness can be studied on the hybrid account offered here.

7.4 Awareness as a Functionally Emergent Kind

In the next two sections I argue that if awareness is an instance of functional emergence then there are mental states whose status as aware or not is indeterminate . In other words, sometimes there is no answer to the question “did you see it?” and yet awareness is still a real and scientifically respectable phenomenon.

So, what is it to say that awareness is an instance of functional emergence? Emergence here is not to be understood mysteriously, but rather as a result of the organisation of a system. To say something is emergent in the relevant sense is to say that a system with the parts organised as they are as a whole has different properties to a system with identical parts organised in a different manner (Bunge, 1977; Schier, 2010; Wimsatt, 2007). The kind of emergence of interest here is ‘functional’ because the relevant parts are functional kinds. A functional emergence account of awareness is one on which consciousness is constituted by two or more cognitive functions organised in the right way. Which functions matter and what ‘the right way’ means vary depending on the details of the hypothesis. Importantly it is organisation that unites the component processes into a whole non-arbitrary unit.

Functional emergence accounts of awareness have been advocated in both the philosophical and scientific literatures. From philosophy, Dennett’s (1991) multiple drafts account of awareness is such an account. On his account consciousness is identified with certain effects a mental content has on the cognitive system (via the processing of the vehicles representing that content). As multiple effects are hypothesised to be characteristic of awareness, these being effects on report, action control and memory etc. multiple processes must be identified as underlying awareness.

From the neurosciences we have functional emergence accounts in the guise of various forms of the Global Workspace hypothesis. Varieties of this hypothesis identify awareness with mental representations in a global workspace, where the global workspace is understood as a set of functions. For example, in presenting their version of the Global Workspace hypothesis, Dehaene and Naccache state that:

The vast amounts of information that we can consciously process suggests that at least five main categories of neural systems must participate in the workspace: perceptual circuits that inform about the present state of the environment; motor circuits that allow the preparation and controlled executions of actions; long-term memory circuits that can reinstate past workspace states; evaluation circuits that attribute them a valence in relation to previous experience; and attentional or top-down circuits that selectively gate the focus of interest. (Dehaene & Naccache, 2001, pp. 13–14)

We see here that for a particular mental representation to be in the global workspace is for it to fulfil several functional roles. Here, Dehaene and Naccache are positing that a subject is aware of a stimulus if the representation of that stimulus can be used to prepare and control actions, enable long-term memory of the stimulus, be emotional evaluated and be the subject of top down attention. Even when the global workspace is understood in neural, rather than just computational, terms the networks identified as potentially part of the workspace are identified on functional grounds. Specifically, Dehaene and Naccache hypothesise that specific networks could be part of the workspace because the kinds of connections they show to other networks means they could underlie the functions they identify with awareness (Dehaene & Naccache, 2001, p. 15).

Importantly not all broadly functionalist accounts of awareness are functional emergence accounts. In particular accounts which identify awareness with a single function or processing of mental states cannot be functionally emergent in this sense. An example of this type of single process theories is Prinz’s (2000, 2012) account which identifies awareness with a particular type of attentional processing which we met in Chapter 6. Dehaene and Naccache’s do hypothesise that top down attention is necessary to get a mental representation into the global workspace (Dehaene & Naccache, 2001, p. 14). However, they are careful not to identify awareness with this function alone. On their view top-down attention makes a mental representation available to the global workspace, but the content of the representation is only in the workspace if it fulfils all of the necessary functions which constitute the workspace. That is whilst this kind of attention is necessary for awareness only all of the functions which constitute the workspace are together sufficient for awareness.

To get more of a grip on what functional emergence is, let’s consider a non-cognitive example: making chocolate. Chocolate making was introduced to the study of the mind by Coltheart (2002) as an example of a modular process to explicate the roll of dissociations in cognitive neuropsychology. The example, as it turns out, is also of an instance of functional emergence, namely chocolate making. Coltheart asks us to consider an example of chocolate making using a set of organised modules, where each module performs a single specific function as in Fig. 7.1.

Fig. 7.1

The functional organisation of a chocolate maker, after Coltheart (2002)

This particular organisation produces 3 different outputs, cocoa powder, sweet chocolate or milk chocolate, but the making of anyone of them (as well as the making of all 3 considered as a whole) is an instance of functional emergence. In Fig. 7.1 each box represents a function that needs to be performed in order to make chocolate. To explain the making of chocolate we need an account of how each function is performed. Yet providing this for each box, i.e. component function, would be insufficient to explain chocolate making. If the performance of the ‘refine’ function is not correctly linked to the output of the ‘grind’ function, it will not be possible to make chocolate. For reasons such as this we need an account of how the components are organised. Something like this is sketched by the functional description in Fig. 7.1.

Now, suppose we were trying to figure out, without asking someone who knows, what function the factory described in Fig. 7.1 is performing. By assessing the input and output of the factory we could determine that the function of the factory is, unambiguously, to turn raw materials into cocoa powder and various forms of chocolate. Suppose as well, that we aim to find out more about the components of this function by interfering with the factory. Perhaps we give it a small amount of beans such that it could only extract enough cocoa butter for milk chocolate and not for sweet. We could learn important things about the functioning of the factory in this case (Coltheart, 2002, pp. 144–149), such as that the distribution of resources to the processes of making milk and sweet chocolate is not randomly determined.

What if, however, we were to consider such cases where we interfere with the system without considering cases where it is working normally? We might be tempted to conclude, from various dissociations that we could create, that the factory doesn’t function as a whole to produce varieties of chocolate and cocoa, but that it contains several smaller unorganised processes each of which independently produce different products and that our grouping of them together as “making chocolate” is an arbitrary decision based on the fact that they happen to be in the same building.

This is analogous to the examples considered by Irvine. If we take a stimulus that can be processed such that dʹ > 0, but that subject’s cannot accurately report what is present, then we can conclude that the representation of that stimulus is like a conscious representation in that it functions to produce better than chance discrimination, it is unlike a conscious representation in that it doesn’t function to produce reports, long term memories of what was presented or immediate retrospection of what was present. We can name and study these phenomena if we like, but we have no grounds for inferring from this ambiguous case that there is no such thing as awareness, nor that the concept of AWARENESS is not useful. In investigating our chocolate factory, the mere fact that we can, via interference, prevent some processes from occurring doesn’t imply that the machine is not chocolate maker nor that the ultimate output isn’t chocolate, nor that it doesn’t function to make chocolate. Similarly, because there are mental representations that are neither unambiguously processed outside of awareness not unambiguously part of awareness doesn’t imply that there is no such thing as awareness.

Why this conclusion should be resisted isn’t clear, the concepts we use in doing cognitive science typically don’t have clear boundaries, but this rarely plays a role in justifying an elimination of a concept.

So, what are we to say given this and given that we have agreed with Irvine that not one of the processes underlying discrimination, short term memory, deciding to report, report, long term memory, selective attention and the like are sufficient for awareness? What is awareness? Different functional emergence accounts will differ with regard to which claims about processes matter, but in general such accounts posit that awareness is all (or a subset) of these processes organised into a unified whole. A mental representation is unambiguously in awareness when it is processed in all of these ways and unambiguously out of awareness when it is processed in none of these ways. What if it is available for attention, but not discrimination? Or available for discrimination, but not report? Well then it is just ambiguous as to whether or not the subject is aware of it. And what a fantastic outcome this is! It means we now have representations that undergo some of the processes constitutive of awareness, but not others. In other words, we can study the parts of awareness.

We are now in a position to see how functional emergence accounts of awareness could interpret some specific examples. Consider the example from Norman, Heywood, and Kentridge (2013) introduced in Chapter 6. Norman et al. (2013) masked shapes such that subjects were no better than chance at indicating their presence, dʹ not different from 0. Yet when performing a task to indicate the location of objects within those shapes subject’s still showed effects characteristic of attending to the ‘invisible’ shape. Namely, faster responses to objects presented in the same shape as a visible prime than to objects the same distance from the prime but inside a different shape. A functional emergence account would put forward the following sort of hypothesis to describe the phenomenon. A representation of the traced shape is processed in attention and this has certain characteristic effects on behaviour, namely changing reaction times to discriminate objects presented within the shape. That said, no representation of the shape seems to be processed in a manner that would fulfil the functions of discrimination (of the shape from noise) or verbal report. Does this mean that the subject is aware of the stimuli? Yes, in that they attend to it? Or no in that they can’t report or discriminate it? On Irvine’s interpretation of studies of this kind it is assumed that this question must have a determinate answer one way or the other. Yet, on a functional emergence account of awareness it is perfectly acceptable to conclude that these cases are indeterminate . Sometimes, in difficult to implement contrived circumstances, there just is no fact of the matter as to whether or not a subject is aware of a particular stimulus.

7.5 Indeterminacy and Ambiguity on Functional Emergence Accounts

What does it mean to say that it is ambiguous as to whether or not a subject is aware of something? The claim that it is sometimes indeterminate as to whether or not a mental state is processed in or out of awareness is not equivalent to the claim that some mental states merely lie on a continuum between fully unaware and fully aware. Rather it is the claim that sometimes there is no fact of the matter as to whether or not a mental state is processed inside or outside of awareness. A subject is neither aware nor unaware of a stimulus represented by an indeterminate state in this sense. Whereas something lying on the continuum between fully unaware and fully aware is determinate, it is determinately on the continuum.

What does this mean for operationalising these states? Consider first something lying on the continuum between fully unaware and fully aware. How would we know this is the right way to characterise it? If a mental state (say a visual experience of a briefly presented stimuli) is on the continuum then we will have converging measures which indicate that the subject was “a bit conscious” of the stimulus. Proposed measures which are designed to be sensitive to such cases include the perceptual awareness scale (PAS) which explicitly allows subjects to describe their experiences as, e.g. “A brief glimpse….” (Overgaard, Rote, Mouridsen, & Ramsøy, 2006, p. 704). Other measures include asking subjects to rate their confidence as to the accuracy of their classification of stimuli, or to gamble on the accuracy of their judgements (Sandberg, Timmermans, Overgaard, & Cleeremans, 2010). Without delving into the issue of the validity of particular measures, if a mental state is somewhere between unaware and aware then measures which can be sensitive to that possibility will agree that the mental state is such. In contrast it is indeterminate as to whether or not a subject is aware or unaware of something (or somewhere in between) if our measures of awareness give contradictory answers, even if we limit ourselves to using measures which are sensitive to the possibility of subjects being ‘a bit’ aware of something.

Importantly there are good, principled, reasons why a functional emergence account predicts indeterminate cases. Characteristic of such accounts is that more than one component process (or function) is constitutive of awareness. A subject is aware of something if (1) they represent that something and (2) the vehicles representing that something are processed in the right ways, but it is the processing or functioning of the vehicle which is thought to be constitutive of awareness (O’Brien & Opie, 1999). Because of the multiplicity of processes which compose the whole organised set of processes which are hypothesised to constitute awareness, such accounts predict the existence of states which are neither aware nor unaware. A subject is unambiguously aware of something if they process a representation of it in all the right ways and those processes are organised into a whole, and unambiguously unaware of it if they process it none of those ways. If, however, it only undergoes some of the processing that underlies awareness, or if the processes are interfered with such they are not organised correctly, then it is indeterminate as to whether or not the subject is aware of it.

How can functional emergence accounts make sense of cases where a subject is (determinately) ‘a bit’ aware of something? On such a view this is not a matter of whether or not a stimulus is processed simpliciter, but rather, what about the stimulus is processed. Consider a case where a subject is presented briefly with a picture of a car, such that they can confidently report the gist of the stimulus, i.e. that the saw a car, but not what kind of car. On this account it is wrong to say that the stimulus is processed unconsciously as something about the stimulus (the gist) is processed so as to meet all of the functions that compose consciousness (assuming all relevant measures agree). They are not fully aware of the stimulus because the detail of the stimulus (e.g. what kind of car it is) has not been so processed. If such a situation were to occur it would be right to conclude, on this account, that the subject was “a bit” aware of the stimulus, but determinately so. It is indeterminate as to whether or not the subject is aware of such a stimulus if (valid) measures of consciousness provide contradictory answers as to whether or not the subject is conscious of it. We can now see that the apparent contradictions in the answers to the question “did you see it” can be resolved as an artefact of imposed categoricality.

7.6 Functional Emergence and the Methods of Cognitive Science

So then, it doesn’t follow from Irvine’s arguments that AWARENESS should be eliminated. Her arguments are consistent with functional emergence accounts of awareness and seem to support the revised concept of AWARENESS used by such hypotheses. But, where would this leave a science of consciousness? Can such accounts avoid the methodological worries raised by Irvine?

First, let’s return to the type A argument from Irvine that awareness cannot be distinguished from processing outside of awareness. Specifically, her argument that methods of dissociation cannot be applied to awareness. To a large degree functional emergence accounts agree with Irvine here, but not in a manner that suggests the elimination of AWARENESS. Consider again that there are some stimuli which subjects can discriminate (dʹ > 0), but not report; thus, suggesting a dissociation between the capacities for discrimination and for report. As I argued above, on functional emergence accounts a dissociation between these capacities is a dissociation between parts of awareness and not of distinct entities.

If we favoured a global workspace explanation of consciousness, then such findings would be accounted for in the following way. A mental content about a stimulus is conscious if it is in the global workspace, meaning that the subject can discriminate signal from noise and verbally report it (and any of the other functions which constitute the global workspace). When a stimulus is discriminable, but not reportable, then it is not globally available and thus the subject is not aware of it. But neither is it processed entirely outside of awareness, because it is used for discrimination, i.e. by a part of the global workspace.

The failures of dissociation to clearly distinguish awareness and processing outside of awareness raised by Irvine are expected on a functional emergence account. Again, the tool being used is the notion of a mental state which is not determinately processed wholly inside or outside of awareness. But, on such an account it should be possible to dissociate determinately processed in awareness, determinately outside of awareness and indeterminate states.

To see how this can be done consider the different response profiles each kind of state should exhibit. If a subject is determinately aware of a stimulus then a representation of that stimulus will fill all the functional roles that constitute awareness. On a global workspace account this means that it is globally available, i.e. it fulfils all of the functions which constitute the workspace. In the signal from noise task a subject is determinately conscious of stimuli which they can discriminate (dʹ > 0) and report and remember and so on (how we go on depends on our theory of consciousness ). It is indeterminate if only some of these functions are fulfilled, as always, it is discriminable but not reportable. Thus, dissociation methods can be used to distinguish awareness from indeterminate processing.

What about processing determinately outside of awareness? Well we can reasonably conclude that if a stimulus cannot be discriminated from noise, reported, attended to or remembered that determinately the subject is unaware of it. If so, then we can dissociate processing determinately outside of awareness from the others on such a task. But this is a hollow victory; for if we presented a stimuli to the back of a subject’s head or didn’t present it at all they would show the same response profile. The worry then is that this account might imply that the only way for a subject to be determinately unaware of something, is for no information about that thing to get into the mind of the subject. This then would mean that, on functional emergence accounts, all mental states are determinately processed in awareness or else their status is indeterminate . This would seem to make the notion of indeterminate states vacuous and undermine any of the work they do in the above arguments. We may as well identify ‘aware’ with ‘reportable’ and call everything else unconscious processing. A vacuous position indeed. What then, is a determinately unaware, but still mental, state or process?

The easiest case to identify is a mental representation which influences the construction of states which are determinately in awareness or indeterminate states, but which never, itself, is processed in the right ways for the subject to be aware of it. The most uncontroversial such states are the assumptions built into subjects’ sensory systems which guide the construction of precepts from noisy/ambiguous sensory stimulation. Examples such as this are already used by advocates of versions of the Global Workspace hypothesis to identify states determinately outside of awareness. Dehaene and Naccache list the computation of location from inter-aural timing differences and the rules of verbal grammar as mental content which is determinately outside of awareness (Dehaene & Naccache, 2001, p. 16). As such, on an understanding of consciousness as a functionally emergent kind the normal cognitive science use of dissociations does apply.

What then of the hope of convergent measures of awareness? Recall the type B argument that Irvine raised against the use of the methods of cognitive science in the study of awareness. If it is the case that measures of awareness never converge, or only converge when they index a specific process like discrimination, then wouldn’t it be arbitrary to group a set of processes together and call them awareness? It would indeed, but the appearance that measures of awareness don’t, or even rarely, converge is an artefact of focusing on noisy and briefly presented stimuli. If we allow into our analysis a broader set of cases, then we do see convergence of measures. If we use supraliminal stimuli, then both verbal report and dʹ measures indicate that subjects are aware of the stimuli. A more interesting example comes from the study of the rubber hand illusion.

Recall that the typical way to operationalise the rubber hand illusion (RHI) is via questionnaire report. If in the experimental condition subject’s agree more strongly with test items like “it felt as if the touch was coming from where I saw it on the rubber hand” than during control conditions and more then they agree with control items like “I felt as though I had two right hands” then they can be said to experience the illusion (Botvinick & Cohen, 1998). This kind of report measure converges nicely with measures which test subjects’ reaction times to visual stimuli presented on or off the rubber hand. When looking at one’s own hand subjects respond faster to visual stimuli present on their hand then the same stimuli presented near the hand (Hari & Jousmaki, 1996). Similarly for the RHI. Subjects respond faster to stimuli presented on the rubber hand when the illusion has been induced, but not during control conditions (Short & Ward, 2009; Whiteley, Spence, & Haggard, 2008).

Here we see convergence across two very different measures of awareness, questionnaire report and reaction times to visual stimuli. Either or both measures can be used to operationalise the rubber hand illusion. Yet, because these two measures are so different it is not an option for Irvine to explain this convergence away as convergence on a particular cognitive process. By her own standards questionnaire report and reaction to visual stimuli are different cognitive processes. By allowing such cases into our analysis alongside the important dissociations Irvine focuses on, we see that there is convergence across measures of awareness that is necessary for doing a science of awareness.

7.7 Revision or Elimination?

One thing that is clear from Irvine’s argument is that our pre-theoretical concept of CONSCIOUSNESS (if there even is a single, stable concept) and many concepts of conscious popular in analytic philosophy (such as QUALIA) are insufficient for understanding, and ultimately explaining, all the experimental findings about conscious awareness. We are faced with the need to either eliminate or revise our concept of CONSCIOUSNESS. Here I have argued that a particular revision, one that involves a splitting of explanations of phenomenal qualities and awareness, explain phenomenal qualities in terms of quality space and offering a functional emergence account of awareness, is not threatened by Irvine’s arguments.

In opting for revision over elimination we must ask: on functional emergence accounts is there anything left that deserves to be called “awareness”? Irvine thinks there is not. She dismisses Dennett’s functional revision of awareness because it isn’t accepted as an account of consciousness in large parts of the analytic philosophy literature (Irvine, 2012a, p. 147). She says that to many:

…it just does not look like an account of consciousness, and states that many of the standard intuitions and puzzles about consciousness are nonsensical. (Irvine, 2012a, p. 148)

In other words it seems to some that a functionalist revision would leave us with a concept of CONSCIOUSNESS that is so different to the one held by analytic philosophers that we should favour elimination over revision.

To reject a revision to CONSCIOUSNESS on the grounds that it does not square with the concept of CONSCIOUSNESS used in some of the analytic literature is unconvincing. Indeed, it would be very surprising if a concept of CONSCIOUSNESS which preserves all of the traditional analytic worries could survive serious investigation. The pre-theoretical concept of CONSCIOUSNESS used in this literature not only faces empirical problems (such as those identified by Irvine), but also internal conceptual problems. The notion of CONSCIOUSNESS at play seems to combine many different, and possibly incompatible, concepts of CONSCIOUSNESS (see Block’s, 1995, famous reproach that CONSCIOUSNESS is a mongrel concept). Additionally, such concepts of CONSCIOUSNESS, especially the concept of QUALIA, often assume that consciousness is necessarily a supernatural phenomenon (Carruthers & Schier, 2017; Dennett, 1988). Worse still the argument ignores the tradition of attempting to revise our concept of CONSCIOUSNESS within this literature, notably started by Nagel when he pointed out that the concept of CONSCIOUSNESS he was using needed revising in order to evaluate whether or not materialism could be true (Nagel, 1974, p. 450).

More generally Irvine’s eliminativism is no less counter-intuitive than revision, and so it would be inconsistent for Irvine to reject attempts at revision on the grounds that they are counter-intuitive. One could follow Jackson and say that elimination is always to be preferred because if you change the concept you are no longer talking about the same thing (Jackson, 1998). This does rule out the possibility of revision, but it is in tension with Irvine’s more general robust naturalism. More importantly this view of the nature of conceptual change is not only controversial it is rejected by revisionists such as Dennett (1988). This means that if it were used to argue for elimination rather than revision the argument would beg the question. The controversial nature of the premise required to make the objection stick, again highlights that Irvine has not sufficiently addressed the revised concept of AWARENESS used by functionalists, rather than pre-theoretical, concept of CONSCIOUSNESS at play in the literature.

There is a substantive point of difference lurking in the wings here. That is the question of how could we choose between elimination and revision. Is the idea that awareness is an organised set of cognitive processes (i.e. a functionally emergent kind) just too different from how we usually think about awareness for it to be worthy of the name? To invoke a familiar analogy is AWARENESS on such accounts more like PHLOSTEGEN than THE EVENING STAR? This is an important question that is worth asking, however, notice that we have now changed the topic. We now need to determine if the phenomenon of interest, namely awareness, exists but is different from what we thought (like the evening star) or if the phenomenon simply does not exist at all (like phlostegen). Is there a phenomenon that can only be explained by the unified functioning of the system, as with the chocolate factory? Or is it the case that there is nothing but the diverse individual functions? On functional emergence accounts there is something left that deserves to be called “awareness”. Namely, the unified whole of cognitive functions (those ones that the accounts identify with awareness). This is just how the account differs from Irvine’s. In order to support eliminativism Irvine’s argument needs to go an extra step and show that this revision fails to describe the actual world, but she offers no argument for this except that it is counter-intuitive to some analytic philosophers. This argument fails by Irvine’s own standards as her eliminativism is equally counter-intuitive.

The other counter-intuitive notion at play in functional emergence theories is the notion of indeterminate state. Can our concept of AWARENESS survive the idea that sometimes there is no fact of the matter as to whether or not a subject is aware of a stimulus? The worry is not whether or not there is anything which deserves to be called awareness (which is Irvine’s concern), but rather that the idea of indeterminate states is deeply counter intuitive. Can our concept of AWARENESS survive the idea that sometimes there is no fact of the matter as to whether or not a subject is aware of a stimulus? Yes. The issue here isn’t so much the revision of AWARENESS as the addition of a new concept, an INDETERMINATE STATE. That is a state which shares properties with those states which are conscious and those which are mental, but unconscious. Does this mean that some things we might think subjects are aware of, turn out not to be? Yes, but that’s okay, we must allow some variation in this or else we would think that the very notion of revising concepts is incoherent. In other words, this objection would also beg the question against the claim that we should revise rather than eliminate.

7.8 Conclusion

Irvine argued that AWARENESS does not refer to a scientifically respectable kind and so should be eliminated. This argument is premised on her interpretation of apparent contradictions in the answer to the question “did you see it?” Yet these apparent contradictions are predicted and explained as an artefact of the artificial categoricality of measures of awareness on functional emergence accounts of awareness. Sometimes there just is no answer to the question “did you see it?” The revised notion of AWARENESS at play here, which understands consciousness as the organised functioning of multiple cognitive processes, is not threatened by Irvine’s arguments. As such the hybrid account offered here, which agrees that awareness is a functionally emergent kind, is not threatened by Irvine’s arguments.

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© The Author(s) 2019

Glenn CarruthersThe Feeling of Embodimenthttps://doi.org/10.1007/978-3-030-14167-7_8

8. Conclusion

Glenn Carruthers[1]

(1) School of Psychology, Charles Sturt University, Port Macquarie, NSW, Australia

Glenn Carruthers Email: gcarruthers@csu.edu.au

Taking the feeling of embodiment, the feeling that my body is me, as a case study, I have attempted to explain consciousness. Specifically, I have attempted to develop a cognitive model of the feeling of embodiment. That is, an explanation of the feeling of embodiment in terms of mental representations and computations. In doing so I have argued that, at the cognitive level, there are two phenomena that need to be explained in order to explain consciousness. These are, first, the phenomenal qualities of the feeling of embodiment; and, second, the subject’s awareness of (or access to) those properties. I have thus offered a hybrid view of consciousness, one that explains phenomenal qualities and awareness as distinct, but related, phenomena. Although developed with regards to a particular experience: the feeling of embodiment, I will be bold enough to hypothesise that an account of this general form will generalise to all consciousness. Let’s finish off with a summary of what the model being offered here is in both specific and general terms.

The phenomenal qualities of the feeling of embodiment are a property of some on-line body representation. They are a property of those on-line body representations which match an off-line prototype of what the subject’s body is usually like. Chapter 3 discussed the evidence for the existence of these kinds of body representation, and Chapter 4 examines the information used to determine a match. In Chapter 4, I also discussed reasons to believe that on-line body representations are points in a conceptual/quality space called ‘body space ’ which is an abstract space constituted by dimensions corresponding to the discriminable properties of bodies (i.e. the ways in which we can tell bodies apart). The best evidence for this comes from studies into the rubber hand illusion, but the model predicts that similar evidence will be obtainable for any body part and for whole bodies, and it shows great promise in explaining the remission of somatoparaphrenia. A match between an on-line body representation and an off-line prototype is constituted by the vehicle of the on-line representation falling in a particular region of body space around the off-line prototype . Thus, when an on-line body representation in this region is elicited, that is a particular vehicle is tokened, the vehicle of representation carries the feeling of embodiment, but the feeling of embodiment itself is explained by that region of body space .

So far, we have one estimate of a hand space , with dimensions being a combination of how hairy the hands were and their apparent gender (hairy/male versus not hairy/female), the position of thumb relative to the rest of the hand (far versus near), the size of the gaps between fingers (fingers pressed together versus fingers spaced widely apart) and, the thickness of the fingers themselves (thin versus thick). One benefit of this account is that it specifies a clear research program in looking for such spaces and how the change during illusions like the rubber hand illusion.

Putting this in general terms, this account follows Clark (1993) in explaining phenomenal properties in terms of particular regions of conceptual/quality spaces. Anything which we can experience as having phenomenal qualities is represented by the mind in a conceptual/quality space. That is, represented along dimensions which correspond to how those things can be discriminated from one another, with distance in the space defined by those dimensions representing the perceived similarity between things (according to some metric). When something is represented in this way, the representing vehicle is to be understood as a point in the space. This vehicle has the phenomenal qualities it does in virtue of the region of the space it falls. Particular representing vehicles thus have phenomenal qualities, but those qualities are explained by regions of conceptual/quality space.

Phenomenal qualities are not all there is to consciousness, however. When we have experiences, yes, those experiences have qualities via which we can distinguish them, but they also appear to the subject. That is to say, the subject is aware of them. On the account offered here phenomenal qualities are properties of particular representing vehicles, but we mentally represent much more than we are aware of. So, is it that those representing vehicles that don’t enter the subject’s awareness are a different kind of representing vehicle to those that constitute the subject’s awareness, as a vehicle theorist would have it? Or, rather is it awareness is a spate phenomenon to representing, say making use of representing vehicles as a functionalist would hypothesise? I introduced this problem in Chapter 5. In Chapter 6, I used the empirical difficulty in distinguishing veridical reports of experience from confabulations in disorders of body experience (anosognosia for hemiplegia and somatoparaphrenia) to argue that a functionalist approach to awareness is more likely to be true. One major problem being that vehicle theories which explain phenomenal qualities and awareness as the same phenomenon (e.g. in terms of representing vehicles in regions of conceptual/quality spaces) have great difficulty even specifying what confabulations are.

What then is awareness of the feeling of embodiment? I considered this in Chapter 7, where I also argued that another good reason to favour a functionalist approach to awareness is that there is a version of a functionalist hypothesis which is immune to Irvine’s powerful argument that awareness is not a scientifically respectable kind. Awareness, then, is a functionally emergent kind. To be aware of the feeling of embodiment is to have the vehicle of an on-line body representation, falling near an off-line body prototype in body space , undergo a set of computations, say those related to verbal report, memory and whatever explains how we fill out a questionnaire. These processes are not independent, but are organised into a whole, such as a global workspace, or being a Dennettian ‘winning draft.’ Awareness of the feeling of embodiment is constituted by this kind of processing of a vehicle of an on-line body representation. Again, a benefit of this approach is that it offers a research program in studying awareness, specifically studying these computational processes and how they are organised.

In general, this hypothesis extends to awareness of anything. Awareness of something, or that something appearing to a subject, is constituted by a representing vehicle being used by a system such as a global workspace. Exactly which processes and their organisation are open to ongoing empirical debate.

That then is consciousness. Consciousness is composed of phenomenal qualities and the subject’s awareness of those qualities. Phenomenal qualities are properties of representing vehicles, explained by the region of conceptual/quality space those vehicles fall into. Awareness is a particular (functionally emergent) kind of processing those vehicles. To further develop and test this account we need to focus on attempting to discover and specify conceptual/quality spaces and determine exactly which processes, and how they are organised, constitute a global workspace/being a winning draft.

Reference

1. Clark, A. (1993). Sensory qualities. Oxford: Clarendon Library of Logic and Philosophy.

Author Index

A

Aglioti, S.

B

Baier, B.

Berti, A.

Besharati, S.

Botvinick, M.

Brock, S.

C

Chalmers, D.

Chatterjee, A.

Clark, A.

Cocchini, G.

Cohen, J.

Coltheart, M.

Cutting, J.

D

Damasio, A.

Dehaene, S.

Dennett, D.

Descartes, R.

de Vignemont, F.

E

Ehrsson, H.H.

F

Flanagan, O.

Folegatti, A.

Fotopoulou, A.

G

Gallup, G.G.

Gao, X.

Gärdenfors, P.

H

Haggard, P.

Heilman, K.M.

Hohwy, J.

Holmes, N.P.

I

Ijsselsteijn, W.A.

Invernizzi, P.

Irvine, E.

J

Jackson, F.

Joseph, R.

K

Kammers, M.P.M.

Karnath, H.O.

L

Lloyd, D.

Longo, M.R.

M

Mangan, B.

Marcel, A.

McGeoch, P.D.

Meador, K.

Mennemeier, M.

Merwarth, H.R.

N

Naccache, L.

Nagel, T.

Norman, L.J.

O

O’Brien, G.

Opie, J.

Orfei, M.D.

P

Paton, B.

Pavani, F.

Prigatano, G.P.

Prinz, J.

R

Robbins, R.A.

Romano, D.

Ronchi, R.

S

Schier, E.

Schwitzgebel, E.

Shanks, M.F.

Short, F.

Slater, M.

Starkstein, S.E.

T

Tsakiris, M.

Tye, M.

V

Vallar, G.

Van Stralen, H.E.

Venneri, A.

W

Ward, R.

Wilcox, A.

Z

Zampini, M.

Zopf, R.

Subject Index

A

Amnesia

Amputation

Anosognosia for hemiplegia
pluralism
remission of

Artificial neural networks

Asomatognosia

Attention

Awareness
indeterminate

B

BIID

Body
as me
as mine
boundaries of
space

Body integrity identity disorder

Body representation
access to
off-line
on-line
prototype

C

Change blindness

Chocolate making

Computation

Concept

Conceptual space

Confabulation

Consciousness
access
functionalist theory
hybrid theory
indeterminate
operationalisation
peripheral
phenomenal
phenomenology
real problem of
self-consciousness
traditional problems of
vehicle theory

D

Delusion

E

Experience sampling

F

Feeling of embodiment

Functional emergence

Functionalism

Functional magnetic resonance imaging (fMRI)

G

Global workspace

H

Hallucination

Hand
space

Hard Question

Hayling’s sentence completion task

Hemispatial neglect

Heterophenomenology

I

Identity theory

Immediate retrospection

Inattentive driver

Individual differences

Introspection

M

Magnetoencephalography (MEG)

Manual tasks

Matching

Mirror

Multidimensional scaling

Multiple drafts

N

Naturalism

O

On versus off model reaction time

P

Paralysis
acknowledgement of

Paresis

Perceptual awareness scale (PAS)

Phantom limb

Phenomenal qualities

Playing cards

Priming

Princess Elisabeth

Proprioceptive drift

Q

Quality dimension

Quality space

Questionnaires

R

Reaching

Reliability

Repetitive transcranial magnetic stimulation (rTMS)

Report
typing

Representation
explicit
inexplicit
mental
tacit

Representational content

Rubber hand illusion (RHI)
active
virtual

S

Saccades

Self touch

Sense of ownership

Sensory deficits

Similarity

Skin conductance response (SCR)

Skin temperature

Somatoparaphrenia
remission of

Stimulus from noise

Suggestibility

Supernumerary limb

U

Unconscious

V

Validity

Vehicle theory

Vestibular stimulation

W

Wada test

Weakness

X

Xenomelia