A REFLEXIVE SCIENCE OF CONSCIOUSNESS
Department of Psychology
University of London
In Ciba Foundation Symposium 174 Experimental and Theoretical Studies of Consciousness. 1993, pp 81-99, Chichester: John Wiley & Sons.
KEYWORDS: consciousness, subjective, intersubjective, objective, private, public, first-person, third-person, repeatability, symmetrical access, asymmetrical access, reflexive, science, reductionism.
Classical ways of viewing the relation of consciousness to the brain and physical world make it difficult to see how consciousness can be a subject of scientific study. In contrast to physical events, it seems to be private, subjective, and viewable only from a subject's first-person perspective. But much of psychology does investigate human experience, which suggests that classical ways of viewing these relations must be wrong. An alternative, Reflexive model is outlined along with it's consequences for methodology. Within this model the external phenomenal world is viewed as part-of consciousness, rather than apart-from it. Observed events are only "public" in the sense of "private experience shared." Scientific observations are only "objective" in the sense of "intersubjective." Observed phenomena are only "repeatable" in the sense that they are sufficiently similar to be taken for "tokens" of the same event "type." This closes the gap between physical and psychological phenomena. Indeed, events out-there in the world can often be regarded as either physical or psychological depending on the network of relationships under consideration.
However, studying the experience of other human beings raises further complications. A subject (S) and an experimenter (E) may have symmetrical access to events out-there in the world, but their access to events within the subject's body or brain is asymmetrical (E's third-person perspective vs S's first-person perspective). Insofar as E and S each have partial access to such events their perspectives are complementary. Access to S's experience is also asymmetrical, but in this case S has exclusive access whereas E can only infer its existence. This has not prevented the systematic investigation of experience, including quantification within psychophysics, psychometrics, and so on. Systematic investigation merely requires that experiences be potentially shared, intersubjective and repeatable. In this the conditions for a science of consciousness are no different to a science of physics.
I am always rather puzzled when people ask whether it is possible to have a science of consciousness, for the reason that much of psychology is a science of consciousness in spite of it's frequent protestations to the contrary. Many of the papers to follow, for example, will elaborate on recent ways in which psychological and related brain sciences are getting on with the study of conscious experience rather than agonizing over whether such a study is possible, and this has been true of experimental psychology since it's inception in Wundt's Leipzig laboratory. How, for example, could one study colour vision, perceptual illusions, emotions, dreams, imagery, and the like, without making a systematic study of conscious experience, it's relation to environmental input, to brain processing, and so on?
So, why is it that in much philosophical, psychological, and other scientific writing a scientific investigation of consciousness has been thought to be difficult if not impossible? The reason, I suggest, has to do with a deep-seated confusion about how consciousness relates to the brain and physical world, that permeates the entire Dualist vs Reductionist debate.
Figure 1. A Dualist model of the causal sequence in visual perception.
Light rays from a cat (as-perceived by an Experimenter) impinge on the
Subject's eye. Impulses travelling up the optic nerve produce a neural
representation of the cat within S's central nervous system. CNS activity,
in turn, has a causal influence on S's mind, resulting in a percept of
a cat. It is central to this model that the percept (of a cat) in the mind
of S is quite separate both from the neural representation (of a cat) in
S's brain and the cat (as-perceived by E) out-there in the world (taken
from Velmans, 1990).
Consider, for example, the conventional model of perception shown in Figure 1. Viewed from the perspective of an external observer E, light rays travelling from the physical object (the cat as-perceived by E) stimulate the subject's eye, activating his optic nerve, occipital lobes, and associated regions of his brain. Neural conditions sufficient for consciousness are formed, and result in a conscious experience (of a cat) in the mind of S. From E's perspective, the physical and neurophysiological causes of S's experience are (in principle) observable, but not their perceptual effect (the experience itself). E nevertheless infers that S has an experience, for the reason that when he turns his gaze toward the cat he experiences it himself.
It is clear from this simple model why consciousness is often thought to elude scientific study. From E's perspective, the cat is seen to be out-there in the world; it appears to be public, objective, and viewable from an external, third-person perspective. Consequently, a scientific study of cats presents no philosophical problems. By contrast, S's experiences seem to be private, subjective, and viewable only from S's first-person perspective. If so, how can they form a data-base for science? Dualists and Reductionists have very different reactions to this problem. For Dualists, S's experience may be a non-material substance or entity, with no location or extension in space (represented as a "cloud" in Figure 1); consequently, Dualists may accept that a study of consciousness is beyond natural science. For Reductionists, S's experience will eventually be shown to be nothing more than a state or function of the brain (Figure 2). If so, the study of consciousness may be safely left to some future neurophysiology.
Figure 2. A Reductionist model of the causal sequence in visual
perception. Light rays from a cat (as-perceived by an Experimenter) impinge
on the subjects eye. Impulses travelling up the optic nerve produce a neural
representation of the cat within S's central nervous system. This CNS activity
is subjectively experienced as a percept of a cat (in the mind of
S) but neurophysiological discoveries will show this subjective experience
to be nothing more than a state of or function of S's brain (taken from
I do not intend to rehearse the pros and cons of these positions, as
do not believe the nature of consciousness can be understood in either
Dualist or Reductionist terms. The intractability of the problems posed
by consciousness arises not from irresolvable Dualist vs. Reductionist
differences, but from unfounded assumptions that they share. The
models shown in Figures 1 and 2, for example, take it for granted that
experiences are separate from the external physical world; in so
far as experiences are thought to be anywhere, they are "in the
mind" or "in the brain." The physical world, on the other hand, is "out-there"
beyond the body surface.
Figure 3. A Reflexive model of the causal sequence in visual
perception. Light rays from a cat (as-perceived by an Experimenter) impinge
on the Subject’s eye. Impulses travelling up the central nervous system
produce a neural representation of the cat within S's central nervous system.
Information within this neural representation is incorporated within an
'experiential model' of the cat produced by the brain in the form of a
cat as-perceived by S. This is 'projected' by the brain to the judged location
of the initiating stimulus, out-there in the world. As in the Dualist and
Reductionist models the the neural representation of a cat in S's brain
is separate from the cat (as-perceived by E) out there in the world. Contrary
to these models, however, S's percept of a cat and the cat as-perceived
(by S) are one and the same. Indeed what S experiences is similar to what
E experiences, viz. a cat out there in the world, but viewed from S's perspective
rather than from the perspective of E (taken from Velmans, 1990).
I have argued, by contrast, that the Dualist and Reductionist models need to be replaced by the Reflexive model shown in Figure 3 (cf Velmans, 1990a, 1992a,b,c; see also commentaries by Gillett, 1992; Rentoul, 1992; Wetherick, 1992). This differs only in the final step. As before, perception is initiated by some entity or event innervating sense organs, afferent neurons, and cortical projection areas, along with association areas, long-term memory traces and so on; as before, neural representations of the initiating event are eventually formed within the brain - in this case, neural representations of a cat. S also has an experience of a cat. But according to the Reflexive model, there is no experience of a cat "in S's mind," or "in S's brain." While S is gazing at the cat, his only experience of the cat, is the cat he sees out there in the world. If he is asked to point to his experience, he should point not to his brain but to the cat as-perceived, out-there in space beyond the body surface. In this, S is no different from E. The cat as-perceived by S is the same cat as-perceived by E (albeit viewed from S's perspective rather than from E's perspective).
Thus, the Reflexive model makes the conventional assumption that representations of external events are formed within the subject's brain, and that under appropriate conditions these are accompanied by experiences of the represented events. Unconventionally, it also suggests that the brain models the world by reflexively projecting experiences to the judged location of the events they represent. On this view, the world as-experienced (the phenomenal world) is a representation, formed by sense organs and perceptual processes that have developed in the course of human evolution. Being part-of consciousness, the phenomenal world cannot be thought of as separate from consciousness (contrary to Figures 1 and 2). This has profound consequences for whether the study of consciousness can be a science.
Note that if the phenomenal world is just a representation, it cannot be the thing itself. Physics and other sciences, for example, may represent the events we experience in a very different way; non-human animals exposed to the same events, but equipped with different sensory and perceptual systems, are likely to inhabit different phenomenal worlds.
Although this way of thinking about the world as-experienced may seem odd to those accustomed to thinking in either a Dualist or Reductionist way, it follows a tradition in philosophy dating back to Immanuel Kant, and the scientific evidence for perceptual projection in visual, auditory, and tactile sense modalities is considerable (cf Velmans, 1990a). I do not have space to recount that evidence here. However, for anyone who doubts that the phenomenal world could be a perceptual projection, recent work with virtual realities may provide a quick, convincing demonstration. Current virtual realities are crude. Nevertheless, they give the appearance of being surrounded by simple, virtual objects in a three-dimensional virtual world through which one can move and with which one can interact. This virtual world is entirely a perceptual construction based on computer generated images, fed to goggles, which are co-ordinated with body movements, and in some systems with tactile stimuli administered via gauntlets. This simulates the pattern of stimulation arriving at the senses that one might expect when interacting with entities and events in the actual world. In the Reflexive model, the creation of such projected, virtual realities is easily explained - the computer generated input stimuli simply tap into the same perceptual processes that construct the everyday phenomenal world.
Without further ado, therefore, let me turn to the consequences of the Reflexive model for a science of consciousness.
PUBLIC VERSUS PRIVATE EVENTS
As noted above, the privacy of conscious experience is often thought to place it beyond scientific investigation. Physical events, by contrast, are thought to be public. In the words of the philosopher Curt Ducasse,
"In the case of the things called "physical" the patent characteristic common and peculiar to them, which determined their being all denoted by one and the same name, was simply that all of them were, or were capable of being perceptually public - the same tree, the same thunderclap, the same wind, the same dog, the same man, etc., can be perceived by every member of the human public suitably located in space and time. To be material or physical, then, basically means to be capable of being perceptually public." (Ducasse, 1960, p85).
The Reflexive model suggests a very different view. In this model, what we ordinarily refer to as the "physical world" is simply the world as-experienced around our bodies. This phenomenal world, being part of consciousness, is private to each human being. In the same way that you cannot experience my pain, you cannot experience my experience of a mountain, or a tree. In short, all experienced events are private, whether they be inner events (such as thoughts and dreams), events in the body, or events out-there in the world. In Figure 3, for example, the cat as-perceived by E is private to E; and the cat as-perceived by S is private to S. Consequently, any description E or S give of the cat, is necessarily a description of their own private experience. At first glance, the consequences for science seem to be those spelled out by the father of operationalism, the physicist P.W. Bridgman, in 1936. In the final analysis, Bridgman concludes, "science is only my private science."
Yet, as Ducasse points out, there clearly is a sense in which some entities and events are also "perceptually public." The entity under observation in Figure 3, for example, can be perceived to be a cat by both E and S, and by any other member of the public suitably located in space and time. But if each phenomenal cat is private, what is it about the cat, that is "perceptually public"?
Recall that in the Reflexive model, objects as-perceived represent things-themselves, but are not identical to them. The thing which is perceived (by E and S) to be a cat, for example, might be described in a very different way by physics. Consequently there may be something about a thing-itself that is public in spite of the fact that each experience of it is private. When a thing is located beyond the body surface, for example, it may be accessible to the exteroceptors of any normally functioning human being. Consequently, things-themeselves may be "public" in the sense of public accessibility.
Further, to the extent that things are subject to similar perceptual processing in different human beings it is reasonable to assume a degree of commonality in the way such things are experienced. While each experience remains private, it may be a private experience that others share. Consequently, experienced things (phenomenal objects and events) may be "public" in the sense of private experience shared.
SUBJECTIVITY AND INTER-SUBJECTIVITY
Once an essentially "private" experience becomes "public" in the sense that others have similar (private) experiences, there is also a transition from subjectivity to inter-subjectivity. Each private experience is necessarily subjective in that it is always the experience of a given observer; once that experience is shared with another observer it becomes inter-subjective. To the extent that an experience can be generally shared (by a community of observers) it can form part of the data-base of a communally grounded science.
Note that intersubjectivity in this sense does not entail an absence of subjectivity, i.e. it does not entail the existence of some observer-free "objectivity" even for observations and measurements in natural science. As Chalmers (1990) points out, science has developed many techniques for circumventing the idiosyncrasies of human perception, involving standardised procedures for translating data into meter readings, computer printouts and so on. Consequently, anyone following the same procedures should get the same results. In this way, he claims, "observations become objectified." However, the repeatability of observations does not make them observer-free.
In the Reflexive model each observation results from an interaction of the observer with the observed; consequently each observation is observer-dependent, and unique. If the conditions of observation are sufficiently well-standardised the observation is repeatable, in which case intersubjectivity can be established by collective agreement. Note that different observers cannot have an identical experience; even if they observe the same event they each have their own, unique experience. Intersubjective agreement merely requires their experiences to be sufficiently similar to be taken for "tokens" of the same "type." This applies particularly to scientific observations, where "repeatability" requires intersubjective agreement amongst scientists observing similar events at different times and in different geographical locations.
In sum, observed phenomena in natural science are
(1) public only in the sense of "private experience shared"
(2) inter-subjective rather than "objective"
(3) repeatable only in the sense that they are sufficiently similar to be taken for "tokens" of the same "type."
This re-analysis of the public, intersubjective, repeatable nature of physical phenomena applies equally to phenomena more usually thought of as "conscious" or "psychological," such as images, pains, and the like. For example, prolonged focusing on a red circle, produces a red circle after-image. Each after-image is private, yet the phenomenon is public in the sense that anyone with normal vision focusing on the red circle under suitable conditions should have a similar experience, i.e. it is intersubjective and repeatable. Pain is often taken to be a paradigm case of a private, mental event within philosophy of mind. Nonetheless, the claim that aspirin diminishes certain forms of pain is publicly testable; if the claim is true, pain reduction should be a shared experience that is intersubjective, and repeatable.
Within the reflexive model such parallels between physical and psychological phenomena are to be expected for the reason that the entire phenomenal world is part of consciousness. Consequently, the phenomena we call "physical" are just a subset of the things we experience. Indeed, such phenomena can often be thought of as either "physical" or "psychological" depending on the network of relationships under consideration - a point made by the Neutral Monists Ernst Mach (1885), William James (1904), and Bertrand Russel (1948). As Mach puts it
"the traditional gulf between physical and psychological research ... exists only for the habitual stereotyped method of observation. A colour is a physical object so long as we consider its dependence upon its luminous source, upon other colours, upon heat, upon space, and so forth. Regarding, however, its dependence on the retina ... it becomes a psychological object, a sensation. Not the subject, but the direction of our investigations is different in the two domains."
In this situation, the traditional gulf between a subjective first-person perspective and an external observer's third-person perspective is equally fine. Each experienced phenomenon results from an interaction of the observer with the observed. If the observer is interested in the nature of what is observed (for example, the nature of what is out-there in the world), he may be said to adopt a third-person perspective. If he is interested in the nature of his own experience (of the observed) he may be said to adopt a first-person perspective. But the observer's experience does not change as he changes perspectives! All that changes is his focus of interest and, consequently, the relationships under consideration.
However, the study of conscious experience usually involves an interaction
between at least two observers, an experimenter (E) and a subject
(S). This raises a number of further complications.
SYMMETRIES AND ASYMMETRIES OF ACCESS
Consider, once again, the cat in Figure 3. If E and S are both interested in the cat, and use similar (exteroceptive) perceptual systems and equipment to observe it, we can say that their access to it is symmetrical. But suppose E is an experimental psychologist and is interested not in the cat or in his own experience of the cat, but in S's perceptual processing and consequent experience.
In a typical psychology experiment, S might be asked to attend to the cat (now thought of as the "stimulus") while E shifts the focus of his attention to S, for example, to events taking place within S's body and brain, or to S's reports of what he experiences. From E's third-person perspective, the processes taking place within S's body and brain are, in principle, observable. S might infer the existence of such processes, but while he focuses on the cat he cannot observe them. Consequently, the access E and S have to S's perceptual processing is asymmetrical. In this situation, the differences between E's third-person view of S, and S's first-person view of himself are considerable. From E's point of view, this poses no problem as he has access to the information he needs.
In other situations, E and S both have access to events relating to S although their access remains asymmetrical. S, for example, may have insight into the nature of his own psychological problems (via feelings and thoughts), which E might investigate by observing S's brain or behaviour. In medical diagnosis, S may have access to some malfunction via interoceptors, producing symptoms such as pain and discomfort, whereas E may rely on what can be viewed from the outside, via E's exteroceptors (vision, touch, and so on) supplemented by instrumentation. In these situations, neither E nor S's perspective is automatically privileged. In so far as E and S each have partial access to the same condition their perspectives are complementary (cf Velmans, 1991a, section 9.3; Velmans, 1991b, sections 8 and 9).
Access to S's experience is also asymmetrical, but in this case S has exclusive access to the experience whereas E can only infer its existence. From E's point of view this does pose methodological problems, as information about S's experience can only be obtained indirectly, for example from S's verbal description or some other communicative response. This has not prevented a systematic investigation of experience, including quantification of experience (e.g. within psychophysics and psychometrics) although methodological solutions have often required considerable ingenuity (see, for example, Ericsson & Simon, 1984; Finke & Shepard, 1986; Libet, 1985; Pope & Singer, 1978).
A NON-REDUCTIONIST SCIENCE OF CONSCIOUSNESS
Reductionists retreat from a science of consciousness into a form of "third-person perspectivism" which denies the legitimacy of S's experience, while simultaneously asserting the legitimacy of E's experience (of S). If the Reflexive model is correct, this exclusive faith in E (at the expense of S) loses its foundation. S's consciousness is not some ephemeral "cloud" that requires reduction in order to make it respectable for science, but his entire phenomenal world. This is formed by perceptual processing interacting with represented entities and events, but does not reduce to such processing. The phenomenal world of E is no different. Consequently, the experiences of S and E are equally legitimate.
From their respective vantage points, E and S have symmetrical access to some entities and events and asymmetrical access to others. Whether E's third-person view of S, or S's first-person view of himself is privileged depends entirely on what is being accessed and what requires explanation. One can err from either perspective.
E has access to S's brain states and behaviour, but S has access to his own experience. Consequently, a complete psychology requires the information accessible to S to be related to the information accessible to E (cf Velmans, 1990b). If experiences are to form a data-base for science, they merely need to be potentially shared, intersubjective and repeatable. In this respect, the conditions for a science of consciousness are no different to the conditions for a science of physics.
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Marcel: When you used the term intersubjective, were you using it in the sense of conventional psychology, i.e. that there is a shared consciousness or that each person knows what the other is conscious of? It seems to me you are using it in an unconventional sense, whereby something is intersubjective merely because a lot of people see it. Normally, intersubjectivity is where each knows and there is a mutuality.
Velmans: But how do you establish that mutuality? I was saying, basically, your experience is subjective to you, my experience is subjective to me. By exchange of information, we establish our shared subjectivity, and thereby our intersubjectivity or mutuality.
Marcel: No. There are several approaches to intersubjectivity that do not rely on linguistic exchange, for example, those that appeal to Verstehen, to simulation, or to the idea of a 'virtual other'.
Nagel: Max, it seems to me that you are introducing an unnecessary puzzle in asking where is the head , when you look at a hologram of a head. The head is the intentional object of my perceptual experience-what it is a perception of. Of course, the object of my experience is located in the box, but my visual experience of seeing a head in the box is in my head. Are you denying that?
Velmans: Yes. I would say that you are giving a characterisation of your visual experience that misrepresents what you actually experience! You make a distinction between the intentional object of perceptual experience (the head as experienced), which you agree is out in the world, and your experience of a head, which you claim is in your head. But when you look at the hologram, you don't have an experience of the holographic head in your own head. The only visual experience you have is of a head in a box, out in the world.
Nagel: I don't say that I experience the visual experience of the head as being in my head. I just say it is in fact an event taking place in my brain. If we want to locate the mental event in space, its, location is in my head. There is absolutely no incompatibility between that and locating the intentional object of that perceptual experience outside my head. These are really two completely different levels of description of the thing.
Velmans: I agree that ‘a head as experienced’ and ‘an experience of a head’ are two ways of describing the same thing. In the reflexive model, all observations involve an interaction of the observer with an observed. The phrase 'a head as experienced' focuses our attention on what is observed; the phrase ‘an experience of a head’ focuses our attention on the role of the observer. The two phrases are logically distinct, but they do not refer to events that are phenomenologically distinct. This is precisely my point. There is only one phenomenal head, and it is out there in the world.
That said, the reflexive model assumes exactly what other models assume about events taking place in the physical world and in the brain. So there are external physical events, representations of those events in the brain, influences of memory and consequent experiences. The whole story is the same. The only thing that is being challenged is the notion that experiences of events out in the world are in the head or brain. The only experience I have of the holographic head is the head I see out in the world. William James made the same commonsensical point, as did Kant, Russell, Whitehead and other theorists. The value of using a hologram of a head in a box to demonstrate this point is that we all know there really isn't a head in the box - it's only a three-dimensional image. So it's easier to get away from the notion that the experience of a head can’t be out there in the world, because there is something already occupying its place - the object itself. But what applies to holograms applies in general. According to the reflexive model, perceptual processes in the brain reflexively project experiences to the judged locations of the events and entities those experiences represent.
Harnad: The object of the experience is out there, but the experience is inside, in the head. When one asks where the experience is, one is not asking about the locus of the object of the experience but about the locus of the experience. You seem to be conflating the two.
Gray: The reflexive argument seems to me to have an intuitive plausibility in vision. But what happens when I'm sitting with my eyes closed and listening to a string quartet on a gramophone? Where is the string quartet?
Velmans: The reflexive model calls a spade a spade for all phenomena. So if you are wearing earphones and you experience a symphony orchestra distributed in the space within your head, the reflexive model says the experience is within your head. The particular examples I was dealing with had to do with physical events out there in the world, because those are the ones that cause most of the problems.
Gray: You are telling me that in each case the experience is where it feels it is. But I'm asking about your reflexive model. In the reflexive model, you say there is a cat, there is the representation in the brain which is then reflexively projected back out to where the cat in fact is. How do you do that with the string quartet?
Velmans: What you are drawing attention to is that there are a number of natural subdivisions within the contents of consciousness, for example, events experienced to be out in the world, events experienced to be within the body or on its surface, and inner events without a clear experienced location. According to the reflexive model, the brain continuously attempts to produce a phenomenal representation of events, including a phenomenal representation of their location. So, when events originate in the world, the brain projects the corresponding events as experienced out in the world. An event that has its origin within the body, once processed by the brain, results in a bodily experience. Inner events such as thoughts and dreams relate to the processing of the brain itself; consequently, they are experienced to be in the head or to be without a clear location. So, if there really is an orchestra out there in space, you will normally hear the sounds out there in space. If you listen to the orchestra through earphones, you will usually hear the sounds inside your head. According to you, experiences are always inside the head. I agree that brain states are always inside the head, but this is not true of experiences. In the case of sound, this occurs only under special conditions.
‘Inside the head locatedness’ has been studied by Laws (1972). He investigated the acoustic differences between white noise presented through a speaker (perceived to be out in the world) or through earphones (perceived to be inside the head), using probe microphones placed at the entrance to the auditory canal. This revealed spectral differences produced largely by the pinnae of the ear being bypassed under one condition but not the other. He then devised an electrical equalising circuit that would simulate the effects of the pinnae. When the equalising circuit was switched into the earphone circuit, noise presented through earphones was experienced to be out in the world; when the circuit was switched out, the noise was experienced to be inside the head.
So all the reflexive model says is that the brain makes judgements about the location of events on the basis of the information it receives. Normally, in the case of sounds, information about location is provided by auditory cues, some of which are produced by spectral changes produced by the pinnae. If you produce those changes artificially, the brain judges the source of sound to be out in the world and projects the experienced sound to the judged location of the source. When pinnae effects are absent, the brain concludes that the source of sound cannot be beyond the pinnae, and 'inside the head locatedness' results.
Searle: There is a commonness view that I think you may be denying; I'm not sure. Suppose I listen to a string quartet; I sit here and they are over there, and I listen to them play the music. Then I go home and I put on my earphones and listen to a tape of the same music. In both cases, there was an experience that occurred in my head. In both cases, there was an external cause of that experience. Are you denying that?
Velmans: I am saying there is a difference between those two situations. If there is an orchestra out there in space, you will hear the sounds out there in space. If you put the earphones on, you will hear the sounds inside your head. All the reflexive model says is, on the basis of the information that is arriving in the brain, the brain makes a decision about where the source of information is. Normally, the information about location is provided by auditory cues, some of which are produced by the modulation caused by the pinnae.
Libet: It seems to me that the reflexive model Is simply a special case of what's going on all the time - subjective referral. If you stimulate the somatosensory cortex electrically, you don't feel anything in the brain or head at all, you feel it out in your hand or wherever the representation is of that cortical site. That applies to all sensibilities. There is referral away from the brain to the body parts; there is referral out into space, if the stimulus appears to be coming from there. The representations of the neuronal patterns of the brain are not isomorphic with what's coming in, so there is referral not only at a distance, but also in terms of the shape or configuration of the image, which is not identical with the neuronal representation at all.
Velmans: I agree.
Libet: So this is a general property of what's going on, it's not a special thing. On the other hand, to understand and explain subjective referral of neuronal representations is indeed a fundamental question on the mind-brain relationship.
Humphrey: There is an ambiguity which may be creeping in and suggesting this is more complicated than it is. When something happens to our bodies, when light arrives at our eyes or sound at our ears, we can represent that event at our body surface in two ways: either as a sensation, as a bodily event of some significance occurring at the boundary between ourselves and the environment, or as a perception, something happening in the external world. These two can occur in parallel with each other, and to some extent can be dissociated. The same event may be sensed in one way and perceived in another.
Take the example of the remarkable experiments of Paul Bach-y-Rita (1972) on skin vision, in which he used mechanical stimulation on the skin of the back to represent the display from a television camera. In that situation, people can switch between perceiving a visual world of objects in space, public objects shared with other people, and feeling the tactile stimulus on their back as a private event. They have, in effect, a visual percept accompanied by a tactile sensation. You aren't distinguishing these two possibilities, i.e. that the same effect can be represented in these two ways, one of which is external, the other of which is located in one's own body.
Velmans: It's not a problem for the model at all. For a start that's a special case . . .
Humphrey: I don't think it's a special case.
Velmans:. In the case of visual perception, for instance, there is no sense in which you can both experience an object out in the world and experience the retinal image.
For the tactile modality, a similar phenomenon to the one you mention was investigated by Von Békésy (1967). He attached vibrators to both forearms of subjects and studied the effects of varying their frequency and phase relationships. When the phase relationships were arranged in a particular, way, the two vibrators were experienced as producing a single vibration that seemed to jump from one forearm to the other. But if the stimulation continued for a few hours, it was experienced as a vibration out in the space between the limbs.
von Békésy’s real purpose was to throw light on the nature of audition. In audition, the proximal stimulus is vibration of the eardrums, but what you actually hear is a sound out in space. You don't feel the vibration of the eardrums. In situations like those investigated by von Békésy and Bach-y-Rita, the brain is presented with a novel stimulus pattern and it attempts to assess its significance. That assessment may change over time, and as the interpretation of the stimulus changes so may the accompanying experience. Consequently, under some conditions the same stimulus can be experienced in more than one way, and one may also be aware of a transition between experiencing a stimulus one way or the other (a similar effect occurs with the Necker cube).
Wall: But to suggest that I can't experience the red after-image as a sensation belonging to me is just wrong. It moves when I move my eyes; an object in the real world does not. The crucial test of something being mine, which I can move around and manipulate, applies to the red after-image. Therefore, it's mine and it's not an object in the external world.
Velmans: I agree. I don't see why that's a problem for the reflexive model.
Wall: I like your introduction of virtual reality, but there's an important additional property of virtual reality machines. The subject experiencing such a machine has to move his head, move his hands, has to explore. The reason the hologram is better than the best photograph is that you can explore it and discover three dimensions in it. In those situations, where you are exploring the outside world, I understand your reflexive model. But when you explore memory traces inside your brain, you bring no new information from the outside world. Internal and external explorations are quite different phenomena.
Velmans: I agree with you, but again I'm not sure why this is a problem for the model. We experience an after-image differently from an actual object out there in the world, because the relationship of visual stimulation to events in the world is different, and the brain detects that difference. The fast that the retinal stimulation associated with an after-image moves as the eyes move gives the brain the information that the stimulation is associated with the eyes themselves rather than some stable object out in the world. The fact that our bodies move independently of the entities out in the world enables the brain to distinguish what's in the world from what is part of the body. The reflexive model assumes that different functional relationships detected by the brain are likely to result in different experiences. So that's not a problem for the model (see Velmans 1990, p 95).
Lockwood: Could you say more about how you think the kinds of considerations you offered actually provide a way forward in relation to the mind-body problem?
Velmans: One of the fundamental moves that the reflexive model makes relates to the very first question mind-body theories have to address: what consciousness is. When we are talking about consciousness or its contents we have to talk about all the contents, not just the ones traditionally associated with Cartesian dualism, such as images, thoughts and so on. In the reflexive model the contents of consciousness include the entire world as perceived. Once you accept that the entire phenomenal world is part of consciousness, you can no longer think of consciousness as being the insubstantial, non-extended substance proposed by Descartes. While some contents of consciousness (of interest to psychology) remain relatively ephemeral (images, dreams, thoughts), the physical world as experienced seems to be solid and extended in space. According to this way of thinking, inner experiences, body experiences and external objects and events as experienced are just subsets of the contents of consciousness. Consequently, the Cartesian separation of consciousness from what is not consciousness in terms of ‘thinking substance’ versus ‘extended substance’ breaks down.
At the same time, once you accept that the external phenomenal world is part of the contents of consciousness, reductionism loses its appeal. While it might be tempting to reduce some ghostly Cartesian consciousness to a state of the brain to make it respectable for science, to reduce the entire phenomenal world to a state of the brain is absurd. The reason is that states of the brain (of a subject) as observed by a neurophysiologist are just a part of the neurophysiologist's phenomenal world. Consequently, reductionism requires the neurophysiologist to deny the scientific status of the subject’s experience while simultaneously taking for granted the scientific status of his own experience - a form of solipsism that philosophers of mind are usually concerned to avoid.
In the reflexive model, physical events as experienced are included within the contents of consciousness. Consequently, there is no unbridgeable mind-matter separation. This also has consequences for how one thinks about physics and the way physics relates to psychology. According to the model, physical science attempts to ascertain the deeper nature of the external phenomenal world, that is, the deeper nature of the external world that we experience. Strictly speaking, a ‘phenomenon’ isn't a ‘phenomenon’ unless it is observed or experienced (that is, unless it is part of the phenomenal world). Looked at in this way, physics investigates the deeper nature of what is experienced much as psychology does, although the relationships of interest in these disciplines differ.
The reflexive model just assumes that all observers have phenomenal worlds. If their focus of scientific interest is the nature of the external world that they experience, they are probably doing physics (or some other natural science); if their focus of interest is each other, or themselves, they are probably doing psychology (or some related science). These differences of focus are accompanied by different methodological problems. For, example, different observers may have similar, (symmetrical) access to events out in the world. This is taken for granted in physics. But an external observer’s access to events taking place within the body, brain and experience of a subject is likely to be different to that of the subject (asymmetrical access); in this situation, third-person perspective information may differ from first-person perspective information. It may then be necessary to examine the relative utility of first- and third-person information, and to gain a deeper understanding of how these perspectives elate to each other. But this presents no irresolvable metaphysical difficulties. So the model takes you right out of the dualist/reductionist debate.
Shevrin: There is one puzzle I have. Are you offering your reflexive model to explain, for example, intentionality and subjectivity, or do you define them as givens?
Velmans: If intentionality is construed just as something being ‘about something’, the reflexive model simply assumes that the contents of consciousness are representational. Representations, by definition, are representations of something. Therefore, consciousness is intentional because it is representational, but, for me, the property of being ‘about something' isn't peculiar to consciousness. It seems perfectly reasonable to assume that unconscious representational states are also about something; they are constantly used by the brain to organise meaningful interaction with the world. Subjectivity, in the model, is assumed to be unavoidable. It follows from conscious experiences always being the experiences of a given observer, with his/her unique vantage point on the world. In my paper, I argued that there is no such thing s observer-free objectivity, even for physics. We all have experiences, we share them in certain circumstances, we can agree about our experiences in certain circumstances, thereby establishing our intersubjectivity. It is not possible to be an observer without subjectivity. Nevertheless, there is a difference between intersubjectivity and what is purely a subjective experience.
Searle: There is problem about this, and it's what I was trying to get at earlier. 0n the common-sense view there is the world that exists totally independently of any observation whatever. If we all die, that world remains the same: Mount Everest still has snow on the summit and a hydrogen atom still has one electron. Are you denying that?
Searle: Now, if you accept that much, the next step is: sometimes when we experience that world, it impacts on our nervous system in such a way that the external independently existing world causes us to have in our heads conscious experiences of that world.
Velmans: I would say that such experiences are not phenomenally ‘in our heads’; they are phenomenally distributed out in the space surrounding our bodies. But, I agree with the basic point you are making that there really is a world (a thing-itself) that such experiences represent.
Searle: There really is a world, it causes us to have experiences,
those experiences are all in our heads, though of course they make reference
to the world that is not in our heads.
Velmans: But the world is not normally experienced to be inside our heads!
Marcel: Max, there is some confusion here. First, will you accept
the vehicle-content distinction? Are there vehicles out there? Part of
the vehicles are out there in a causal chain. Let me give an example: I
have a pain in my finger at the moment, my finger is on the table, is the
pain on the table?
Velmans: No, the pain is in your finger.
Marcel: But my finger is on the table!
Velmans: I agree that your finger is on the table. And both your finger and the table are experienced to be out in the world - a case of perceptual projection. Suppose you pick up a pen and touch the paper on the table with the pen. Can you feel the tip of the pen touching the paper? If we don't think about it, our impression is that we can feel the tip of the pen touching the paper. That is another example of perceptual projection.
Marcel: That is irrelevant. The content of your experience may refer to what is in the world. But the experience itself is not in the world. The experience (as a vehicle) is in your head.
Dennett: Max, I can't understand your idea of the phenomenal world. I'm going to push you with an example. In the field of robot vision, they worry about such things as whether or not a ‘mote’ in the eye of the robot gets interpreted by the robot as something out in the world rather than something in the robot's visual system. All of the issues about illusion and subjectivity and objectivity have counterparts in this world. You can do an amazing amount of research in so-called robot vision, where all these issues come up again and again. In the sense in which you are talking about a phenomenal world, do these robots have a phenomenal world?
Velmans: My own assumption would be that they don't. I find it perfectly meaningful for people involved in building robotic representational systems to include information about the location of the events with which the robot is required to interact. One essential feature of location information would be: is an event located beyond the robot body surface or isn't it?
I would assume that the brain is doing a similar kind of calculation. The difference, I would argue, is that in the brain the processing doesn't stop there: there is not just calculation going on in the brain. There are, in addition, for reasons we don't fully understand, the conditions for, having a phenomenal world. I would be quite happy to accept that robots and human bodies and brains might be functionally equivalent, in terms of their ability to interact with the world. But, while we clearly have a phenomenal world, I have doubts about the robot.
Dennett: Then I want to know why, as a psychologist, you worry about the phenomenal world and don't just pretend you are doing robotic vision. Every investigatable issue that comes up for you as a psychologist seems to have a parallel version in the land of robot vision.
Velmans: I would deny that. I would say that much of what's investigated in psychology is actually looking at the relationship between how bodies and brains function and how things are experienced. For instance, there is a difference between being able to discriminate between two colours and thereby being able to operate in a functionally appropriate way (say, having a moving device that is triggered to stop by the colour red and to move by the colour green) and actually having an experience of red or green. The whole study of colour vision, its neural antecedents, how different cultures label and categories the colour spectrum in different ways and so on, takes it for granted that humans have a colour phenomenology and that one of the central points of interest is how the phenomenology depends on visual processing or is used in different ways in different cultures.
Bach-y-Rita P 1972 Brain mechanisms in sensory substitution. Academic Press, London
Laws, P 1972 0n the problem of distance hearing and the localization of auditory events inside the head. Dissertation, Technische Hochschule, Aachen, cited in Blauert J (ed) 1983 Spatial hearing: the psychophysics of human sound localization. MIT Press, Cambridge, MA
Velmans M 1990 Consciousness, brain, and the physical world. Philos. Psychol 3:77-99
von Békésy G 1967 Sensory inhibition. Princeton University Press, Princeton, NJ