J. Kevin O'Regan
Laboratoire de Psychologie Expérimentale
Centre National de Recherche Scientifique,
Université René Descartes,
92774 Boulogne Billancourt, France
oregan@ext.jussieu.fr
http://nivea.psycho.univ-paris5.fr

Alva Noë
Department of Philosophy
University of California, Santa Cruz
Santa Cruz, CA 95064
anoe@cats.ucsc.edu
http://www2.ucsc.edu/people/anoe/

The aim of our target article was to explain perception and perceptual consciousness. Specifically, we sought to lay out a way of thinking about visual experience (indeed, about perceptual experience more broadly) that can address the explanatory gap for consciousness, that is, the problem of understanding how physical mechanisms can give rise to consciousness (to experience, sensation, feelings).

We are grateful to the commentators (including those whose commentaries were not accepted for publication in this issue). Their criticism forces us to clarify our position.

Broackes, Block, Clark and Toribio, Cohen, Kurthen, Manzotti & Sandini, Lamme & Landman, Laming, Oberauer, Pylyshyn, Revonsuo, and the Editor doubt that the sensorimotor approach provides for a novel solution to the problem of the explanatory gap. We address this issue in this section by formulating more explicitly the reasoning implicit in the target paper.

The explanatory gap for perceptual consciousness has several aspects Following , we can distinguish three different questions that need posing (cf. pp. 234-235).

1. The intra-modal comparative aspect: Why does it look like this (spherical say), rather than like that (say cubical)?
2. The inter-modal comparative aspect: what makes one experience visual whereas another is tactile?
3. The basic question: why is there experience at all?

It is clear that the sensorimotor approach makes a contribution to [1] and [2]. As for [1], the intra-modal aspect, consider that the differences between a spherical and a cubical object of sight correspond in part to differences in laws of sensorimotor contingency. For example, there are systematic changes in the character of the profile of a cubical object as you move around it. These patterns of changes are totally unlike the changes in sensory stimulation that occur as you walk around a sphere. The visual quality of looking cubical is constituted (at least in part) by your knowledge of how your visual stimulation will change as you move around it.

Intra-modal differences pertain to differences in the objects of sight. Inter-modal differences pertain rather to the differences in what you do when you encounter objects through different sensory modalities. Moving your eyes to the left or right will produce a change in sensory stimulation related to an object if that object is being visually perceived but not if it is being tactually perceived, or if it is being listened to. Likewise, stopping and unstopping your ears affects your relation to things you are hearing, but not your relation to things you are seeing. In general, in agreement with a suggestion made previously by , we argue that the sensory modalities differ from one another in that they are governed by different laws of sensorimotor dependency.

But what of the basic question [3]? Can the sensorimotor approach explain why activity drawing on knowledge of sensorimotor contingencies gives rise to experience at all? Several commentators challenge us on this score. Clark and Toribio, for example, write that "Even if the contents of our conscious visual experiences reflect ways of acting in the world, the hard problem surely remains." Oberauer asserts that we are victims of the illusion of thinking that sensorimotor contingencies can do something that neural representations cannot, namely explain the emergence of consciousness. The Editor writes: "The point is that what is seen is felt, not merely registered, processed, and acted upon. To explain consciousness in terms of sensorimotor action, one has to explain why and how any of that processing is felt...".

To make some headway, let us consider a fourth question about the explanatory gap, this one intermediate between questions [2] and [3].

To deal with [2'], compare your visual experience of a book on the table in front of you with your nonperceptual awareness of a book on your desk in the next room. Two features sharply distinguish these two modes of awareness.

Bodiliness. Moving your body makes a difference to the mode of your awareness of the book in front of you on the table but not to the mode of your awareness of the book in the next room. In particular, it is not just any body movements that make a difference, but those that depend on the distinctively visual sensorimotor contingencies. For example, blinking, eye movements, body or head movements modulate your relation to the book in front of you but make no difference at all to the book in the next room. Furthermore, if you reach out to move the book, or wave your hand to obstruct it, or to cast it in shadow, there will be a change in way the book affects your sensory systems. Such movements make no similar difference to the way you are affected by the book in the next room.

Grabbiness. The visual system is put together in such a way that sudden changes in the visual field provoke an automatic orienting reflex. For example, if a mouse moves the book suddenly, or if the lighting on the book changes abruptly, this will grab your attention, and cause your eyes to flick to the book. Thus, movements or changes in the book immediately affect your sensory stimulation (just as movements of the body do): you are (so to speak) "connected" to the book. On the other hand, there is no such sensitivity to movements of the book in the next room.

Bodiliness and Grabbiness affect your relation to the book in front of you, but not your relation to the book in the next room. This is what the difference between perceptual awareness and nonperceptual awareness (or thought) comes down to. We suggest that it is precisely the way in which sensory stimulation is affected by movements of the body (bodiliness) and movements of (or changes in) the object (grabbiness) which give sensory experience its peculiar, sensory, character. In other words, bodiliness and grabbiness explain not only the difference between seeing something and merely thinking about it (thus answering 2'), but they also explain why seeing something has the sort of qualitative characteristics that it does. And crucially, bodiliness and grabbiness are concepts defined strictly in functional terms, thereby providing a functional basis for the difference between sensory and non-sensory experience.

With these considerations in place, we can now go further and try to make clear how, with bodiliness and grabbiness, the sensorimotor approach provides the key to closing the explanatory gap. says that what characterises phenomenality is that there is "something it is like" to have a sensory experience. Let us be more precise and try to characterize exactly what it is like, taking visual experience as an example.

First, visual experience is visual, rather than, say, tactual or olfactory.

Second, it is forcibly present to your consciousness. Third, it is ongoing, that is, the experience seems to be happening to you in a continuous way: its subjective character lasts while the experience continues. Fourth, the experience strikes us as ineffable, that is, though you experience it as possessing various qualities, the exact qualitative character escapes description in words.

We believe the sensorimotor approach allows us to explain each of these aspects of the quality of the experience. To the extent, then, that the experience itself is constituted by the presence of just these qualities, then the sensorimotor account can explain why the experience occurs at all (and so it can answer [3]).

First, as we have stated already, the visualness is explained by the character of the sensorimotor contingencies produced by exploration mediated by the visual apparatus and by the character of the sensory changes produced by objects as they move in space.

Second, the sense of forcible presence is explained by (1) grabbiness and (2) bodiliness. (1) the book forces itself on us as present because any movements on the part of the book cause us to direct our attention (our processing resources) to it. (2) The slightest movement of the relevant parts of our bodies modifies the sensory stimulation in relation to the book. Metaphorically, it is as if we are in contact with the book.

Third, we can explain ongoingness in a similar way in terms of bodiliness and grabbiness. The sense of an ongoing qualitative state consists, (a) in our understanding that movements of the body can currently give rise to the relevant pattern of sensory stimulation (bodiliness), and (b) in our understanding that the slightest change in what we are looking at will grab our attention and in that way force itself on us. In this way we explain why it seems to us as if there is something ongoing in us without actually supposing that there is anything ongoing, and in particular, without supposeing that there is a corresponding ongoing physical mechanism or process. Just as our awareness of detail present in the world is explained by the fact that we have access to that detail, and that we know that we do — this is the significance of the idea of the world as external memory () — so our awareness of the experience as ongoing is explained by the fact that we encounter a sensory event whenever we look.

Fourth, the sensorimotor approach can also explain the ineffability of experience. The nature of our contact with objects of perception is determined by the very complicated laws linking commands given along thousands of motor nerves with the associated input received along thousands of sensory input fibres. Obviously these laws, though they are registered and distinguished by the brain, are not themselves what is available for use in our decisions, judgements and rational behavior. We cannot describe the laws -- all we can do is put them to use. Just as we can ride a bicycle, drive a car, and tie our shoelaces without being able to describe in detail everything these skills involve, our sense of the ineffability of experience is explained by the fact that we lack access to the very complicated laws governing sensorimotor contingencies involved in sensory exploration.

We argue that the peculiar sensory quality of perceptual experience derives from the fact that the associated sensorimotor contingencies have bodiliness and grabbiness. However, to be perceptually aware of an object is not only to interact with it in ways drawing on knowledge of sensorimotor contingencies, it is to make use of one’s skillful interaction for guiding behavior and other forms of thought and action (such as speech). This amounts to the requirement that to actually visually experience an item, to see it, one must have a kind of higher-order control of one’s tracking activity. This kind of control corresponds to the particular use we made of the term "awareness", or what and have called "transitive consciousness" : but note, crucially, like sensorimotor contingences themselves, this control is a functionally describable capacity.

We could build a robot with knowledge of sensorimotor contingencies on the one hand, and with the further ability to make use of information about its exercise of this knowledge in its planning and acting, on the other hand. If indeed such a robot were to be embodied and situated in such a way that its perceptual encounters were characterized by bodiliness and grabbiness, then it would be correct to say—and the robot would agree!—that there is something it is like for it to perceive.

In this way we meet Clark and Toribio’s worry about ping-pong playing robots head on. They write: "A good ping pong playing robot, which uses visual input, learns about its own sensorimotor contingencies, and puts this knowledge into use in the service of simple goals (e.g. to win, but not by too many points) would meet all the constraints laid out. Yet it seems implausible to depict such a robot (and they do exist — see e.g. Andersson 1988) as enjoying even some kind of modest visual experience. Certainly, someone could buy into all that O'Regan and Noe offer as an account of how certain visual experiences get their contents without thinking that this in any way makes progress with the hard problem of why it feels like anything at all to be thus in command of a set of well-poised SMCs."

We agree that, at least as described, it is implausible that Clark and Toribio’s ping pong playing robot would be perceptually conscious. But this is exactly what the sensorimotor approach would predict of such a robot. As it is described, it is simply far too simple to be a plausible candidate for perceptual consciousness of the kind usually attributed to animals or humans. This simplicity has several dimensions. For one thing, the robot is missing too much of the background capacities (intentions, thoughts, concepts, language) for the attribution of experiences to it to make much sense. For another, its sensorimotor mastery is reasonably supposed to be pretty simple in comparison with the exceedingly complicated effects of movement on the sensory systems of animals. Nevertheless, we would claim that once we imagine a robot that not only masters sensorimotor contingencies, but makes use of that mastery to engage with the world in a thoughtful and adaptable way, it becomes necessary to say that it has (at least primitive) visual experiences.

Block raises a similar objection to Clark and Toribio's. He points out that the sensorimotor contingencies governing the visual experience of a person who was both paralyzed and almost completely blind would be simple enough that they could be programed into a laptop computer. But it is plainly false, Block reasons, that the laptop would have the visual experiences enjoyed by the nearly blind paralytic. This is meant to be a reductio of the sensorimotor view. The argument fails, however, because it is not a consequence of our view that the laptop would have visual experiences like that of the nearly blind paralytic. The simplest way to show this is to consider that there is no reason to think that programing sensorimotor contingencies into the laptop would give the computer knowledge of sensorimotor contingencies in the relevant sense. By "knowledge" we mean practical mastery, i.e. familiarity with the ways sensory stimulation varies as a function of bodily movement. It is difficult to see how a machine without a body could have this kind of know-how. Another relevant consideration is that, contrary to the laptop, a legally blind paralytic would be able to perceive in other sensory modalities. For example, when the incandescent object comes closer, you would feel its heat. Your limited visual stimulus would be correlated with nonvisual sensory stimuli. But there are other reasons to conclude that Block’s laptop would not have perceptual consciousness. Importantly, the laptop lacks not only capacities for bodily movement, but also capacities for thought and perceptual attention. Suppose that Block’s laptop were now endowed with understanding and with a body that functioned (to some degree) like ours. Of such a robot, it is surely conceivable (indeed probable) that it would be perceptually conscious.

These considerations are related to a second criticism advanced by Clark and Toribio, namely that of "sensorimotor chauvinism", viz. the view that only creatures with bodies exactly like ours can have experiences qualitatively like our experiences. They suggest, in response, that "there seems no a priori reason to believe that every difference in SMC’s will make a difference to the experienced content, even if the SMC’s (some of them, at some level) are indeed active in determining the content..." As Clark and Toribio suggest, the key issue here is level. For instance, we argue that it is reasonable to think of Bach-y-Rita’s TVSS as a kind of vision (quasi-vision, tactile-vision) because there is a level at which the laws of sensorimotor contingency governing vision operate in the domain of TVSS. Of course, TVSS proceeds without use of the eyes or the visual pathways -- thus TVSS is a way of seeing only if we think of it at a sufficiently course grain. Our view thus allows for the judgment that creatures with radically different kinds of physical make up can enjoy experience which is, to an important degree, the same in content and quality. But it also allows for the possibility (indeed the necessity) that where there are physical differences, there are also qualitative differences. To this extent, our proposal deviates from classical functionalism. That is, we are rejecting a certain way of thinking about the multiple-realizability of functional systems. In particular, we hold, as Clark and Toribio are right to point out, that differences in our bodies (and thus in sensorimotor contingencies) will make a difference to our experiential states. One way to put our point is as follows: only a creature with a body like ours could have input/output relations like ours. We agree with the functionalist, though, that it is the input/output relations that matter. Moreover, we agree that it is not intrinsic qualities of the neural material that instantiates brain processes that matter for consciousness. What matters is the patterns of sensorimotor contingency.

It was not our aim to deny that there is experience, nor to deny that experience has qualitative character. Our aim rather has been to explain experience and to explain its qualitative character. We believe that once you have answered the various questions we answer in the target article — what makes a conscious state perceptual as opposed to nonperceptual? what makes an experience a visual experience as opposed to a tactile experience? what makes a visual experience an experience as of a cube rather than as of a sphere? what makes an experience have the qualities that are specific to sensation, namely forcible presence, ongoingness and ineffableness — there just isn’t any qualitative residue left over which still needs explanation. If we use the term "qualia" to refer precisely to this sort of qualitative residue, we claim in the target article that there are, in this restricted sense of the word, no qualia. Let us add a few words of explanation here.

Consider the would-be quale that you enjoy when you see something red (for example). Strawson writes: "Most...will agree that the notion of the qualitative character of colour-experience can reasonably be taken for granted. And for present purposes, a sufficient reply to those who disagree is simple, as follows. Consider your present visual experience. Look at the bookshelf. (Get out some of the brightest books.) There you have it." We are inclined to respond to this argument in two ways. First, we are inclined to point at the fact that our visual experience appears to us as being sensation-like (rather than thought-like, say) in that this experience consists precisely in being red (and not some other color, nor a sound or smell, say) and in that the experience imposes itself on us in a forcible and ongoing way. These are precisely the features of the experience that the sensorimotor view explains. The experience is as of red rather than as of green thanks to the subtly different patterns of sensorimotor contingency governing our encounter with the red surface (as compared to a green one). The presence and ongoingness of our experience consist in our continuous access and in our ever-ready responsiveness to the redness (to knowledge of sensorimotor contingencies with their associated bodiliness and grabbiness).

There is a second way we are inclined to respond to Strawson’s argument. It is not at all clear what we are commanded to do. "Look at the bookshelf....There you have it." When you look at the books, what do you encounter? The books. Do you encounter all of them all at once? No. But you have access to them all at once and wherever you do look you find a book. So you take them to be there in front of you and to be aware of them (in the sense that you are connected to them by laws of sensorimotor contingency that you understand). But all of this isn’t something that just happens, as it were, in a flash. It is something you do. You move your eyes here, there, back and forth, now here, now there. You think about what you see. You notice this, are distracted by that. The experience you have looking at the books is not something that occurs in you or to you, it is something you do. And when you catalog what you do in acting out this experience, you don’t need to count any additional residue over and above the eye movements and the books and their qualities (such as the red quale).

This idea is challenged by Broackes on something like Rylean, ordinary-language grounds. "The experience of swimming in the rain," he writes, "is something we get while performing that act. The swimming is something we do, the experience is not." Broackes' point seems to be that although having an experience often involves doing things such as, exploring with your eyes, your fingers, sniffing your nose, etc., the things that you do don't constitute experiences, rather they provide experience.

We agree that this is certainly what people say and believe. However we suggest that people are wrong: in fact your belief that you are in a special kind of "seeing redness" state (when looking at an apple, say) derives from the fact that you are connected to the redness in a special, very intimate way, by virtue of bodily, grabby sensorimotor contingencies. Any movement of your eyes produces a change in stimulation you are receiving from the apple. Any movement of the apple (or change, e.g., in its illumination) will grab your attention. It is as if we are in a state which is saturated by the feeling of redness, when in fact we are only poised and attuned and ready and expectant and capable.

It was taking this stance that allowed us to bridge the explanatory gap and to make a number of empirical predictions. This idea is at the core of our approach. Admittedly, it is counter-intuitive.

Broackes is certainly right that we move too fast against qualia when we say that qualia are meant to be properties of experiential states and there are no such states. Our dismissal of qualia was meant to apply only to the restricted notion of qualia conceived as the residue which cannot be accounted for from a functional approach. In particular, we can certainly agree with Broackes that standing for a few minutes in front of an Ellsworth Kelly painting can put you into a kind of perceptual "state" and keep you there. We deny, though, that there is any sense in which this supposed state is unitary. To be in such a "state" consists in several things. Your atttitude to the painting is organized by your thoughtfulness, your attentiveness, by the manner in which you look at the picture and reflect on it. We believe that even when we stop to appreciate the redness in the painting, say, that we are not "receiving" an atom-like quale. Instead, we are at that moment, integrating into our rational behavior, our current mastery of the sensorimotor contingencies of red.

Blackmore criticizes our account of qualia from a different perspective, namely the standpoint of Dennettian skepticism about consciousness. She cites Dennett with approval: "...the actual phenomenology? There is no such thing." And she presses against us the thought that in admitting that there are facts of the matter about perceptual phenomenology we are sliding back into the Cartesian Theater. Dennett’s heterophenomenological perspective is a rich, provocative and important one. Its strength consists in its ability to take on board all the offerings of first-person reflection while dissociating those offerings from claims to privilege or metaphysical insight. It may be — indeed it is likely — that our phenomenological analysis can be accommodated by heterophenomenology.

Block, Harnad, Kurthen, Cohen venture the criticism that ours is just a new version of (a tired old) behaviorism. This criticism might seem plausible in so far as we deny that there are qualia (in the restricted sense of an inexplicable qualitative residue: see 6.3, 6.4 of the target article and R3 above) and we assert that we can explain perception in terms of patterns of interdependence between stimulation and action (which certainly has a behaviorist stimulus-response ring to it). But there are important differences between our view and any version of philosophical behaviorism with which we are acquainted. First, as stressed in R3 above, we do not deny that there are experiences or that experience has qualitative character. Second, our theory takes as primitive the idea that perceivers have knowledge of sensorimotor contingencies. The basis of the qualitative character of experience, on our view, is the perceiver's knowledge of the interdependence between stimulus and bodily movement. Third, according to the sensorimotor approach, it is not the case that mental states (experiential states) are logical constructions of actual and possible behavior states.

Said in another way, our explanation of sensory consciousness is not simply based on sensorimotor contingencies. Sensory consciousness, we say, arises when the person is currently making use of the fact that certain sensorimotor contingencies are being obeyed. For this to be the case, the brain must be doing more than just S-R. First, it must have abstracted from the sensorimotor contingencies categories which allow them to be classified into different sensory modalities and, within these, into different categories like red, blue, green. This is a form of concept formation, and is not just learning of behaviors, contrary to what Van Gulick suggests. Second it must be making use of the fact that these sensorimotor contingencies are currently being obeyed. This is concept manipulation as might be done in an expert system or AI device. All this is therefore not behaviorism.

Block also criticizes us for being behaviorist. He writes: "O’Regan and Noë declare that the qualitative character of experience is constituted by the nature of the sensorimotor contingencies at play when we perceive." He characterizes sensorimotor contingencies as a "highly restricted set of input-output relations." The problem for us, he states, is that our view would appear to have two "clearly wrong" consequences: (1) that any two systems that share the highly restricted set of input-output relations are experientially the same; and (2) that any two systems that share experience must share the highly restricted set of input-output restrictions. Contrary to what Block thinks we claim, Block explains, "experience is a matter of what mediates between input and output, not input-output relations all by themselves".

However, Block has represented us incorrectly. Sensorimotor contingencies are laws describing input-output relations. But it is not sensorimotor contingencies, as such, that "constitute" the qualitative character of perceptual experience. It is the perceiver’s exercise of mastery of laws of sensorimotor contingency that provides the basis for the character of experience. Our relation to our environment when we perceive is bodily and grabby and it is this fact, together with the fact that we implicitly understand the nature of this relation, that explains the qualitative nature of experience. In light of this clarification of our position, consider, first, that this is hardly behaviorist reductionism. As said above, our view depends on the attribution of knowledge to the perceiver. Second, this means that we can accept Block’s observation that experience mediates inputs and outputs and is not simply constituted by those relations. We disagree with Block, on the other hand, on the character of that mediation. For Block the inputs cause experiences in us which in turn cause behavior (output). For us, in contrast, skillful activity (consisting of behavior and sensory stimulation) is the experience. We do not reduce the experience to the input-output relations themselves.

What of the two consequences of our view that Block gives? We reject (1). It isn’t the case that any two systems that share the same input-output relations will be experientially the same, unless, of course, they also agree in their skillful mastery of laws of sensorimotor contingency. They might not, of course. Consider, for example, someone who is adapted to reversing goggles and someone who has just put them on. These two individuals will agree in their input-output relations but they will not agree in experience. (2), on the other hand, seems right: Same knowledge of sensorimotor contingencies, then same experience. It’s worthwhile, though, to repeat a point made above in connection with Clark and Toribio. For two systems to have the same knowledge of sensorimotor contingencies all the way down, they will have to have bodies that are identical all the way down (at least in relevant respects). For only bodies that are alike in low-level detail can be functionally alike in the relevant ways.

Is action necessary for experience? Surely dreaming, meditation, tachistoscopic vision, hearing, pain, perception during paralysis, hallucinations such as phantom limbs, tinnitus, phosphenes, Penfield's experiments — all these are cases where people have perceptions without action being involved, and, as pointed out by Blackmore, Humphrey, Niebur, Nusbaum et al., O'Brien & Opie, Pylyshyn, and Virsu & Vanni, they might pose problems for our approach. Further, Fischer gives an intriguing example where perception of the Zöllner illusion is more veridical without eye movements than with them, which would appear to contradict our theory. To respond to these objections, it is necessary to try to disentangle different strands of criticism. This is our aim in this section.

It is not our claim that action is necessary for experiencing. Our claim, rather, is that knowledge of the ways movements effect sensory stimulation is necessary for experience. It is not movement as such, but the consequences of potential movement that play a role in our view. For this reason there is nothing in our view that rules out contemplative seeing, or that would lead us to think that a paralyzed person would be unable to see (providing that the person had at some time previously had some kind of control over her visual input).

This is enough to make it clear how we can hear even when we hold our eyes and bodies absolutely still. As Virsu & Vanni note, through the course of its development, an organism will have integrated and abstracted laws of sensorimotor contingency particular to each sensory modality. At a later stage, when it is presented with a sensory input which is unambiguously linked to one or other such sensorimotor contingencies, it will implicitly "assume" that if it moved in the appropriate way, the changes in sensory input would be those that are normally associated with that type of stimulation. Thus, since normally input coming through the auditory nerve will change in certain ways when the head or body moves, when later, without moving, the organism is stimulated through the auditory nerve, the stimulation will be perceived as belonging to the auditory modality. This then provides an explanation of audition without head movements. Similar arguments can be made for brief visual stimulations, phosphenes, and stimulation of visual cortex à la Penfield, as well as for phantom limbs.

Niebur gives the example of a "three-dimensional lump of matter, like a mass of modelling clay, that is somehow moved by internal actuators in a complex, unpredictable way, without you having any possibility of influencing or predicting its motion and the forces it exerts on your hands (i.e., there is no 'mastery')." Niebur continues, "According to the claims of the target article, the lump should not be perceived since the perceiver does not interact with it in "lawful" ways. This seems absurd; the lump will surely be perceived, and probably quite vividly so." First of all, we would not expect the subject to fail to perceive the lump just because its movements relative to the hands are actuated from within. Many laws of tactile-motor contingency would be in effect. For example, if you withdrew your hands you would no long receive stimulation. There is therefore no reason for doubting one would feel the lump. But let us ask: would one also be able to feel its shape, to feel it as having such and such a shape? It might be very difficult to extract the relevant knowledge of the operative sensorimotor contingencies without actively exploring with your hands.

Pylyshyn writes "while it is true that we often use our visual system to determine our actions, we also use it to find out what is in the world simply because we want to know...– as we do when we watch TV or visit an art gallery or read a book....Much of what we see guides our action only indirectly by changing what we believe and perhaps what we want."

There is nothing in this that we disagree with. Pylyshyn, like Goodale, seems to make the mistake of confusing the claim that seeing depends on capacities for action with the claim that all seeing is for action. Ours is not a theory about what vision is for, it is a theory about what vision is: it is a mode of interaction with the world drawing on knowledge of sensorimotor contingencies.

O’Brien & Opie and Revonsuo raise the question of dreams. Revonsuo believes that the phenomenon of dreaming shows that "the immediate causal conditions sufficient for bringing about the full range of subjective conscious experiences must reside inside the brain". This is so because when we dream we do not (cannot) move our bodies in interaction with the world. O’Brien & Opie make the same point, adding that "many theorists think it reasonable to surmise that dreams and hallucinations indicate something important about the nature of visual experience more generally, namely, that even "veridical" experiences are constructed by the brain, and thus implicate internal representations."

There seem to be two issues here. First, whether our view can account for dreams and visual images. Second, whether neural activity is sufficient for such occurrences. We will discuss the second of these at greater length below in connection with our analysis of the role of brain in consciousness more generally. Here it suffices to point out that our view does not predict that it should be impossible to have visual experiences in the absence of movements. It would predict only that it would be impossible to have visual expriences in the absence of knowledge of sensorimotor contingencies. There is every reason to believe that dreamers possess knowledge of laws of sensorimotor contingency. It is also not part of our view to deny that the brain is not (in some sense at least) the seat of our knowledge of sensorimotor contingencies. We are, then, happy to accept the consequence that neural activity during dreaming is sufficient to produce the resulting experiences.

Although we are not expert in the psychology of dreaming, we are skeptical of Revonsuo’s claim that "the form of dream experience is identical to that of waking experience". In the article we noted that it seems to be a hallmark of dream-experiences that they are unstable with respect to detail. So, for example, as reported by the dream research of Stephen LaBerge (personal communication) in a dream the writing on a sign will be different every time you look at it. Without the world to act as a repository of information, details in the dream are in flux. In light of this we would predict (although we cannot now establish this) that there will be important systematic differences between the content of dreams and waking experiences and that these differences will correspond to the fact that dreamers cannot look around and check how things are, they can only dream that they can do this.

In connection with this family of issues we would like to discuss briefly the suggestion of Nusbaum et al. that we should broaden our account to include not just motor behavior, but attentionally controlled exploration. In a similar vein, Virsu & Vanni suggest the concept of sensori-attentional contingencies. Hochberg (with examples of aperture viewing and interpretation of ambiguous 3D motions) similarly suggests that we should broaden our notion of sensorimotor contingencies to include not just coupling between action and sensory input, but also between different kinds of sensory input, as these are constrained by the nature of the physical world.

The cornerstone of the argument in our paper was the idea that we can close the explanatory gap by developing the consequences of the active, skill-based character of perceptual exploration. Experience arises not thanks to the existence of an internal representation, but thanks to the mastery and exercise of perceptual exploration. This may seem counterintuitive at first, but it enables us, we think, to explain experience without finding a special kind of physical mechanism to generate it. To the extent that the basis of our approach is that experiences are things we do, not things that happen in us, nothing prevents us from adopting Nusbaum et al.'s and Virsu & Vanni's suggestion of using sensori-attentional contingencies instead of sensorimotor contingencies, since both are modes of action. Indeed, we would agree with Nusbaum et al. and Virsu & Vanni that insofar as pattern recognition and classification are concerned, the notions of sensori-attentional contingencies, or equivalently hypothesis testing or matching of sensory input with internal knowledge, are certainly very plausible. Indeed we are convinced that such processes are precisely those that are involved in everyday pattern recognition, and for that reason, as noted by Scholl & Simons, at certain places in our paper we included flicks of attention as well as flicks of the eye among possible sensorimotor contingencies, even if there is no motor component.

A crucial feature of our theory, however, is the involvement of the body in experience. The peculiar, sensory, quality of our perceptual experience consists (in part) in the fact that movements of the body produce changes in our sensory stimulation. The content of perception is certainly in part the result of inferential processes, as O'Brien & Opie stress; but the quality of experience, is determined by sensorimotor contingencies and the bodiliness and grabbiness that goes with them.

R6 Does perceptual consciousness require representations in the head?

Our claims about representations provoked vehement criticism from many writers.

Broackes argues that representations exist, but that they are fragmented, distributed, and multi-level. Pani argues that internal representations must be used in object recognition, and Cohen gives examples showing that the visual system extracts and categorizes information about the environment, and says this shows there are visual representations. Tatler and de Graef et al. give examples of information that is stored across eye saccades, showing the existence of an almost iconic internal representation. Ryan & Cohen and Hardcastle show how information acquired without awareness can influence later behavior, and say this shows there are internal representations. Ansorge et al. remind us of an important body of data showing unconscious influences of visual information on motor responses. Gallese & Keyers cite mirror neurons as examples of internal representations that can be used not only to control actions but to perceive those performed by others. Niebur argues that internal neural responses like oriented bar detectors are transformed versions of sensory input that constitute internal representations.

We are firmly convinced — and the data cited by the commentators provide proof — that the visual system stores information, and that this information — whether acquired consciously or unconsciously, whether iconic or abstract, whether local or distributed — influences the perceiver's behavior and mental states either directly or indirectly. If this is what is meant when it is insisted that perceiving depends on representations, then we do not deny that there are representations.

There is of course another sense in which our view relies on the existence of representations. Knowledge of the laws of sensorimotor contingency themselves must surely be represented. We readily grant this.

However, we reject two other distinct but related claims about the role of representations in perception and perceptual consciousness. The first of these concerns what Marr called "the computational problem" of vision, e.g. what vision does, or what function the brain computes when it gives rise to vision. Marr’s answer, roughly, is that vision is a process whereby the brain transforms one kind of representation into another, specifically, the retinal image into a representation of the three-dimensional scene. In the target article we give two different kinds of reasons for rejecting Marr’s representational account. First, we doubt that we enjoy perceptual experiences with the kind of content Marr’s visual function is supposed to produce. As change blindness, inattentional blindness and other experiments cited in the target article show, we do not have experiences that represent the environment in that way. Second, we doubt that we need representations of such detail in order to explain the sort of conscious experiences we do actually enjoy.

We can have a flawless, unified, continuous experience of the environment without having flawless, unified, continuous internal representations. The reason is that seeing is not contemplating an internal representation, but doing something of a visual nature with the information available to the brain. Schlesinger's interesting example of a representation-less reinforcement learning neural network that tracks objects as though it had representations of them, is a concrete instantiation of our idea. A consequence of the idea is also that there is no need to postulate filling-in mechanisms to fill in the blind spot, saccade-suppression mechanisms and extra-retinal signals to compensate for eye movements, synchrony of neural firing to provide for binding, etc. Indeed, when neurophysiologists find neurons that look like they are fulfilling such functions, we claim they cannot in fact be doing so. Consider a neuron that responds to a virtual contour. How can the firing of a particular neuron, by itself (that is, isolated from the rest of the brain), make me have the impression of a contour? It cannot. But connecting that neuron to other neurons would not appear to help either, because, after all, neural firing, no matter how complex or recurrent or synchronized, is just neural firing, not sensation. A related point concerns the mirror neurons referred to by Gallese & Keysers. Mirror neurons undoubtedly play a role in the processes involved when macaque monkeys recognize gestures. But the role they play cannot be the role of providing the sensation of seeing a gesture! Because if the firing of mirror neurons provided the sensation of recognizing gestures, one would have to postulate some magical sensation-imbuing power to such neurons (or, to the networks that those neurons are connected to…) So what do mirror neurons do? They presumably provide information to the brain circuits which control the multifarious things that macaque monkeys can potentially do when they act in response to gestures.

The second claim about representations that we reject concerns perceptual consciousness: that seeing could be a matter of having certain kinds of representations in the head. The existence of representations of the environment are neither sufficient nor necessary for seeing. That they are not sufficient is shown by consideration of the fact that people people have very nice representations of the environment in the form of the images on their retinas. But having the retinal image does not make people see. Seeing is in the making use of the representation, not in the having of the representation. Because of this, the actual format of the representation (if it's metric-preserving or distorted, iconic or abstract) is less important than whether and how that representation can be put to use in the sensorimotor activity of the organism. The brain may abstract information in the environment into a form that can be used in an open-ended range of applications, as Van Gulick says. But just having those abstract multi-purpose representations does not account for the what-it-is-like of seeing.

Of course, as Tatler and de Graef et al. point out, it is important to investigate the exact nature of information that is stored in the brain, and this can be done in the manner their very interesting experiments suggest. But finding iconic information in the low level, or middle-level visual system does not explain why the world looks iconic to us.

An example of where our approach to the question of internal representations finds support is in the domain of motor control, as pointed out by Smeets & Brenner. If one takes the view that seeing a moving ball is making an internal representation of it, one is easily led to the misconception that this representation should resemble what a physicist would construct, that is a representation where distance, position, speed, and time are linked by coherent physical laws. It then becomes problematic to understand how, as in the Duncker and waterfall illusions and in the flash lag effect, perceived position and perceived speed seem not to be coherently linked, or why size illusions affect lifting force but not grip aperture (cf. Smeets & Brenner). On the other hand such findings are easier to comprehend under our view, according to which perception involves assimilating possibly independently acquired sensorimotor contingencies which have no necessary internal consistency. Velichkovsky & Pannasch also provide an example of an oculomotor distractor effect which may support our view. Lacquaniti & Zago provide further supporting data for the idea that different more or less independent sensorimotor loops are used in perception: judgments of size and distance of moving objects constitute one type of visual perception, but another kind of visual perception, ruled by different sensorimotor loops, is involved in catching objects. Curiously, Lacquaniti & Zago take this to be contrary to our theory, when in fact it is exactly what we predict. Another example is provided by Roberson et al., who show that relative localization of auditory and visual stimuli depends on an observer's conceiving them as bound. This would be difficult to comprehend on a physicist-type view of the representation of the world. Still, in contradiction to our view, Roberson et al. mention neural connectivity between dorsal and ventral streams as possible substrates for binding: this may be the case, but then again, as we suggest, binding need not be instantiated in the brain at all.

Let us also address an interesting apparent paradox pointed out by Tatler and by Scholl & Simons. These commentators argue that the notion of sensorimotor contingency actually requires internal representations: after all, say these authors, in order to register a change in sensory input when a body motion is made, an internal trace (representation!) of the initial and final state must be preserved in order to allow comparison. But the paradox is only apparent. We agree that the visual system stores information from moment to moment, and to some extent from saccade to saccade, and this is what is used to evaluate changes. But these changes are generally not available to awareness, and this stored information is not what is seen! Seeing, as we keep stressing, is not having an internal representation.

Finally, we would like to clarify one misunderstanding. Pace Wright, we do not claim that "all supporters of an internal presentation are committed to there being ‘red neurons’ in the brain." It isn’t clear to us why Wright takes this to be our view. What we do believe is that certain arguments about the neural basis of experience seem to rely on mistakes just like the mistake of supposing that to see red there must be red neurons. As we explain in the target article, the very idea that there is a binding problem would seem to rest on just the assumption that, sensuous contents must indeed be like what controls their rise (to change slightly the phrase of Sellars's that Wright cites).

The role of the brain in perceptual consciousness is another topic on which we have drawn much criticism. Many commentators misunderstand us as denying that the brain is causally necessary for perceptual consciousness. Lamme & Landman ask whether anything other than neural events could explain consciousness and they propose that reentrant processes can do the job. Bach-y-Rita & Haase complain that we seem to be throwing the brain out with the bath water, and suggest the importance of reentrant brain mechanisms as contributing to perceptual consciousness. Revonsuo says that consciousness is a real biological phenomenon in the brain, and notes that dreaming is proof that only the brain, with no input from outside, is necessary for perceptual awareness. Rees & Frith suggest that the superior parietal lobule is a brain locus that correlates consistently with awareness.

It seems probable that only a dualist could claim the brain plays no role in consciousness, and we are not dualists. Our claim, rather, is that many neuroscientists seem to be looking in the wrong direction for an account of the brain-basis of consciousness. We do not think that we will ever discover the Neural Correlates of Consciousness — the neural system whose activity makes consciousness happen, or which is the event of consciousness itself. Our reason for this is straightforward: a visual experience is not an occurrence in the mind, that is produced by neural activity. Seeing is, in ways we explain, something we do, drawing on a range of sensorimotor (and also conceptual skills). Indeed, as we argue in the target article, we think this is what seeing actually seems like. Careful consideration reveals that when you see you do not encounter an inner something that is, so to speak, ongoing, buzzing, continuous. Your perceptual encounter is a state in which you have access and in which you know you have access. This knowledge makes it seem almost as though you are in contact with that to which you have access. But if there is no ongoing, buzzing, continuous state, then there is no ongoing, buzzing, continuous neural process that we need appeal to. (See and for a critical discussion of the NCC research program.)

We can illustrate the point by way of a comparison. Consider what one might call the BCL: the biological correlate of life in humans. Clearly a "contrastive analysis" of the kind defends would show that the heart beat is an extremely reliable indicator of life. Thus the heart beat is a BCL to the same extent as activity in the superior parietal lobule is a NCC. Having isolated this important correlate of life, the next step would then be to ask how it might contribute to generating life, But this would be an error. We should not think that the heart beat generates (or contributes to the generation) of life. What we mean by life is a complicated range of abilities (e.g. the ability to reproduce, respire, grow, eat, move, etc). The beating heart is causally necessary for organisms like us to live. Neither the beating heart, nor any other physiological system or process, or even the sum of all them, generate life. Being "alive" is just what we say of systems that are made up in this way and that can do these sorts of things.

Our claim about consciousness is that consciousness stands to the brain as life stands to the heart. It reflects a simplistic account of what life is, or what consciousness is, to think that the brain produces consciousness or that the heart (or any other physiological processes) produce life.

What then is the correct way to approach neuroscience, in the context of our theory? We suggest that instead of seeking for the NCC, we should seek for the neural mechanisms that underlie each of the many capacities that underlie consciousness. We should not expect them to come together at any unifying locus in the brain. The consequences of this view have not been widely explored as yet. Indeed, Bartolomeo & Chokron note that much work could be done in exploring the neuropsychological evidence in favour of this view (and they discuss an interesting view of unilateral neglect related to the concept of grabbiness) Another interesting line of work in this respect is the research showing separate functions of dorsal and ventral system in visual perception. Goodale notes that we may have got the exact relations between our theory and these two systems wrong, but certainly the fact that there should be separate systems underlying the different facets of visual consciousness is in favor of our approach. With respect to Goodale's criticism of the distinction between apparatus and object-related contingencies, our point was perhaps not clear in the paper: our idea is that a statistical device that analyzed input-output relations would first extract invariants that are related to the way the observer's body changes sensory input. Grasping an object, and properties of objects that influence that grasp are part of this first level of statistics. All these are essentially coded in ego-centric coordinates. At the second level are properties of objects that are invariant with respect to the observer's body, for example: size, color, shape, as considered independently of the observer's position, in other words, in object-centered coordinates. What this means, as found in Goodale's example, is that someone lacking this stage would be able to grasp, but would not be able to describe the shape of an object. It’s worth mentioning that Goodale’s view stumbles on the problem of the explanatory gap. Just what is it, one might ask, about neural activity in the ventral sream that gives rise to visual experience?

Scholl & Simons believe that our approach is just a bric a brac of old ideas, combined to yield an untestable mess.

As concerns our relation to earlier workers, Scholl & Simons, as well as Kim (who also provides evidence in favor of the theory), note the debt we owe to Gibson. Similarity to Gibson in some respects is also noticed by Pylyshyn (who notes an important dissimilarity as well), Velichovsky & Pannasch, and is suggested by O’Brien and Opie (in their citation of Fodor and Pylyshyn’s well-known criticism of the ecological approach). Velichovsky & Pannasch say our work reminds them of the Russian School of the 1960s. No reviewers mentioned Heidegger, Husserl, Merleau-Ponty or Poincaré, who are other giants upon whose shoulders we stand, although one unpublished reviewer also mentioned Bergson.

Our relation to Gibson. Gibson challenged traditional ideas about the information available to the perceiver in visual perception. He argued that the information needed for vision is available in the optic flow and in invariants of the flow under body motions. He rejected the idea that the only information available for vision is that which is available at the retina. We fully endorse Gibson’s viewpoint. The focus of our investigation is totally different however. Our target is the explanation of perceptual consciousness — why is there perceptual experience? why are some experiences distinctively visual whereas others are distinctively tactile? Our proposal is that we should think of sensory experiences as active — as things we do rather than as things that happen in us. In adopting this view we invoke the role of action and the importance of extracting invariants, and so we are indebted to Gibson. But we harness these ideas for quite different explanatory and theoretical purposes.

In other words, whereas Gibson stresses the use of sensorimotor invariants as sources of information, we are stressing the idea that sensorimotor invariants are part of what constitute sensations and perceptual content. We show that Gibson's idea can go farther than Gibson pushed it.

Scholl and Simons suggest that one of our differences with Gibson might be that we place more emphasis on those particular sensorimotor laws that are related to the observer's peculiar, idiosyncratic sensory apparatus. This is both right and wrong. We think the particular idiosynchratic laws peculiar to each human individual are one part of a heirarchy of sensorimotor contingencies. This lowest level defines the ineffable what-it-is-likeness of red, say for me, different from you. But at a higher level of abstraction, there are laws like the laws of how light from surfaces is affected when you tilt them, which are common to most people and define the invariant qualities of red. Perhaps this is more similar to Gibson's affordances, and less dependent on individuals' apparatus.

As concerns the coherence of the theory, Scholl & Simons are right to point out that what we call sensorimotor theory is not composed of one single idea. We obviously were not clear enough in our paper on how the different ideas fit together and on where lies their common motivation. Let us first address the relation between the world as an outside memory idea and the notion of sensorimotor contingency.

The sensorimotor approach and the idea of the world as outside memory. Knowledge of sensorimotor contingencies explains the qualitative character of perceptual experience. We encounter red, as opposed to green, or as opposed to no color, because of the ways our sensory stimulation depends on our movements and also on movements of the colored surface. We experience red because we take our sensory stimulation to be governed by the relevant laws. The idea is extended to perception (as opposed merely to ‘sensation’) as follows: seeing a bottle is knowing how moving the bottle affects sensory input. Only part of the bottle is at any moment being explored. It serves as an outside entity which is immediately available for exploration like a memory is immediately available for recovery. Hence the notion of world as an outside memory. The idea explains the feeling of richness we get even though at any moment we're only in sensory contact with a small part of the stimulus. This is the theoretical link between the two concepts of knowledge of laws of sensorimotor contingency and world as an outside memory. They form a unified structure in our theory.

The relation to change blindness. Scholl and Simons accept that change blindness was motivated by the world as outside memory idea, but mention that other, earlier experiments preceded the recent change blindness literature, and that these had different motivation. In fact the work of McConkie on saccade contingent changes was contemporaneous with a number of similar studies which the first author was conducting involving changes during saccades. These studies were concerned with the question of trans-saccadic fusion and the extra-retinal signal, that is, the question of how successive views of the environment are brought together to give a coherent representation ( ). It was the results of these experiments, which led the first author to the notion of world as outside memory. In arriving at this idea the first author was most helped by MacKay. On the other hand, Brooks and, particularly Stroud, though cited by Scholl and Simons, actually mention the concept only very much in passing. Minsky does indeed make a similar point, as we noted in the target article.

Scholl and Simons question whether change blindess actually provides support for the idea of the world as an outside memory. Scholl & Simons correctly point out that other possibilities are consistent with the phenomenon, that is, that change blindness does not logically entail the world-as-an-outside-memory view. Lamme & Landman actually suggest one such alternative. This is of course no argument against our explanatory proposal, however. In general, phenomena will admit of many possible explanations. The advantage of one explanation over another lies in the way it fits with other theoretical constructs of a theory. We offer an account of perceptual consciousness in terms of knowledge of sensorimotor contingencies and the idea of the world as outside memory that explains a broad range of phenomena such as change blindness, inattentional blindness, sensory substitution, experiments with inverting goggles, the nature of sensory modalities, and so on (as discussed in the target article). Scholl and Simons criticize the theory because they say these phenomena are more or less independent of one another. It's true that they could be independent, but in fact they here are united by one underlying idea, namely that when taken together with the notion of feel as a thing people do, they allow the explanatory gap to be bridged.

Scholl & Simons question whether the theory is testable. Change blindness was one prediction made from the idea of the world as an outside memory (). As said above, although change blindness is compatible with other frameworks, it is striking that no other framework predicted change blindness. Change blindness only became an active paradigm after the first change blindness experiments with the flicker and mudsplash techniques were performed. The McConkie work that Scholl & Simons referred to was done using eye saccades, because McConkie's prediction concerned the problem of trans-saccadic fusion, and not the more general problem of what the sensation of seeing is. The work by Phillips was motivated by the problem of understanding iconic memory, and was ignored until it was resuscitated by the change blindness literature. We therefore consider change blindness, even though it can be explained in other ways, as an instance of how the theory made interesting predictions. Indeed one other worker did predict change blindness, and it was the philosopher , with an idea very similar to ours, namely that there is no time or place in the brain where consciousness "happens".

The "armchair" experiment with colour we mentioned in Section 5.8 of the target article is another counterintuitive prediction which we are currently testing, and which has met with some success (). Different kinds of sensory substitution and the possibility of creating new, previously unfelt sensations, is another avenue we are exploring.

Blackmore, who is certainly the commentator who best understood the spirit of our approach, proposes three additional, fascinating experiments which would also be ways of confirming the theory because they are so counterintuitive. What she calls "scrambled vision" is something we have actually already attempted, but, regrettably, at present without success (in collaboration with C. Tyler). Evidence that it might nevertheless work comes from the well known fact that people who develop scotomas very quickly come to no longer "see" them. On the other hand people with age-related macular degeneration suffer another kind of scrambled vision, to the extent that the buckling of their retinas has the effect of making straight lines look wiggly. Our prediction would be that practise should iron out the wiggles, providing they don't change over time.

What Blackmore calls "manual vision" is a very intriguing proposal. and bears on the question where people locate a sensation. There are modalities, like vision, where qualities are located on the outside object. There are modalities like touch, where they are located on the limb where contact occurs. There are modalities inbetween, like smell and hearing, where there is a sense in which the quality is located on the object outside, and a sense in which people say they experience the stimulation at the locus of the detector, or even at other locations. An example is when you hear a sound inside your head when you listen to music through stereo headphones. As Blackmore rightly says, according to our theory the locus of sensation will depend on the nature of the sensorimotor contingencies, and by changing these laws, it should be possible to change the locus of perception. We are indeed embarking on experiments very similar to those proposed by Blackmore to test this. A suggestion that they will work comes from the rubber arm experiment of cited in our target article, and the related work of on phantom limbs, as well as (cf. also ) work on sensory substitution.

What Blackmore calls "blinded vision" was of course tested to some extent by ) in their famous work on kittens in the kitten carousel. Each kitten received the same visual stimulation, but only one kitten received the stimulation as a result of self-produced movement. As predicted by our approach, only the active kitten subsequently displayed normal visually guided behavior. In humans, similar suggestions as to the importance of action for acquiring sensory proficiency derive from the finding that severe strabismus seems related to amblyopia. However Blackmore's point seems to be that she thinks that this kind of finding should be observable not just during development, but also at a shorter time scale in the mature sensory system. In a certain sense we agree that our approach suggests that since perception is constituted by mastery of sensorimotor contingencies, the brain must be continually updating and analysing the input-output statistics and making use of them to categorize outside events. This suggests that adaptation to re-arrangement of sensorimotor contingencies could be much faster than what one would expect under a more traditional view according to which such adaptation is a matter of brain "plasticity", occurring fairly slowly in response to environmental or body changes, as during maturation for example. The question of course is, how much faster? Such experiments need to be done, but lacking willing subjects at present, we have not been able to embark upon them. Meanwhile we note that the relative speed with which sensory substitution seems to be acquired suggests that adaptation is indeed faster than might be expected from a traditional theory.

The most important claim in the target paper was that the sensorimotor approach allows us to address the problem of the explanatory gap: that is, the problem of explaining perception, consciousness and qualia in terms of physical and functional properties of perceptual systems. While the target article left many of our commentators unconvinced, we think that in our response we have provided a more convincing argument. Our case has been strengthened by introducing two concepts which, though incipient in the target paper, were not properly exploited there. These are the concepts of bodiliness and grabbiness. Bodiliness and grabbiness are physically measurable characteristics of perceptual systems which, when combined with the notion of sensorimotor contingency, explain why sensation has a "feel", and what that feel is like in comparison to other mental states which have little or no feel. We suggest that in this way we have cast the first steps of what might be called an "analytical phenomenology" (or perhaps a "heterophenomenology"?), that is, a scientific account of the experienced qualitative nature of sensations within a given sensory modality, as well as the principles that distinguish sensations across different modalities.

Many commentators misunderstood our claims about internal representations and the role of the brain in consciousness. We hope to have shown in our reply that we are not so extravagant as to claim that the brain contains no information or that it serves no purpose in cognition. On the other hand we hope to have shown how making a shift in the way we think about representations and the role of the brain leads to new ways of understanding the nature of phenomenal consciousness. The shift we advocate consists in suggesting that experience does not involve having an internal representation, but instead involves making use of certain capacities to interact with the environment. Though counter-intuitive at first sight, this approach, in addition to dealing satisfactorily with phenomenology, sheds a new light on previously unconnected phenomena in experimental psychology, and makes empirically testable predictions.

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