Max Velmans, Dept of Psychology, Goldsmiths, London, New Cross SE14 6NW; email m.velmans@gold.ac.uk; URL http://www.goldsmiths.ac.uk/academic/ps/velmans.htm

[On-line background reading based on extracts from chapters in Velmans (1996) prepared for the World Wide Web "Dialogues on Consciousness" course, hosted by the Centre for Consciousness Studies, University of Arizona, Tucson, 1997.]

Abstract. The following extracts with connecting comments suggest a departure point for a definitions of consciousness that preserves its everyday phenomenology while allowing an understanding of what consciousness is to deepen as scientific investigation proceeds. I argue that current definitions are often theory-driven rather than following the contours of ordinary experience. Consequently they are sometimes too broad, sometimes too narrow, and sometimes not definitions of phenomenal consciousness at all. As an alternative, an ecologically valid, reflexive approach to consciousness is suggested that is consistent with science and with common sense.

Keywords. Consciousness, definitions, dualism, reductionism, reflexive model, perceptual projection, science. subjective, objective.

As George Miller (1987) notes, "Consciousness is a word worn smooth by a million tongues." Consequently, progress in understanding consciousness must grapple with the issue of how to define what it is that we are trying to understand. The following extract (from Velmans (1996) "An introduction to the Science of consciousness", in M.Velmans (ed) The Science of Consciousness: Psychological, Neuropsychological, and Clinical Research, London: Routledge) attempts to set some ground rules that seem consistent both with science and with common-sense.

Extract:

What consciousness is taken to be .... is partly a matter of arbitrary definition - and some confusion in the literature has resulted from differences in definition. In the present text we follow the common usage in which the term "consciousness" is synonymous with "awareness" or "conscious awareness" (sometimes "phenomenal awareness"). The "contents of consciousness" encompass all that we are conscious of, aware of, or experience. These include not only experiences that we commonly associate with ourselves, such as thoughts, feelings, images, dreams, body experiences and so on, but also the experienced three-dimensional world (the phenomenal world) beyond the body surface.

In some writings "consciousness" is synonymous with "mind." However, given the extensive evidence for nonconscious mental processing (Dixon, 1981; Kihlstrom, 1987; Velmans, 1991a) this definition of consciousness is too broad. In the present text "mind" refers to psychological states and processes which may or may not be "conscious".

In other writings "consciousness" is synonymous with "self-consciousness." As one can be conscious of many things other than oneself (other people, the external world, etc.), this definition is too narrow. Here, self-consciousness is taken to be a special form of reflexive consciousness in which the object of consciousness is the self or some aspect of the self.

The term "consciousness" is also commonly used to refer to a state of wakefulness. Being awake or asleep or in some other state such as coma clearly influences what one can be conscious of, but it is not the same as consciousness in the sense of "awareness." When sleeping, for example, one can still have visual and auditory experiences in the form of dreams. Conversely, when awake there are many things at any given moment that one does not experience. So in a variety of contexts it is necessary to distinguish "consciousness" in the sense of "awareness" from wakefulness and other states of arousal, such as dream sleep, deep sleep, coma and so on.

The above, broad definitions and distinctions are widely accepted in the contemporary scientific literature (see, for example, Farthing, 1992) although it is unfortunate that some writers continue to use the term "consciousness" in idiosyncratic ways. Agreeing on definitions is important. Once a given reference for the term "consciousness" is fixed, the investigation of its nature can begin, and this may in time transmute the meaning (or sense) of the term. As John Dewey (1991) notes, to grasp the meaning of a thing, an event or situation is to see it in its relations to other things; to note how it operates or functions, what consequences follow from it; what causes it, what uses it can be put to. Thus, to understand what consciousness is, we need to understand what causes it, what its function(s) may be, how it relates to nonconscious processing in the brain, and so on. As our scientific understanding of these matters deepens, our understanding of what consciousness is will also deepen. A similar transmutation of meaning (with growth of knowledge) occurs with basic terms in physics such as ‘energy’, and ‘time.’"

In short, the suggested strategy is to adopt definitions which are informed by science but which are as close as possible to common usage. This provides a relatively non-contentious departure-point from which investigations can begin. As our understanding of the nature of consciousness increases its definition, may, in time become more detailed and precise.

However, the puzzle of "What consciousness is" goes beyond definitional squabbles. In Velmans (1990, 1993, 1996) I argue that there are also deeply-rooted conceptual confusions involved.

In the following extract (from Velmans, 1996, "What and where are conscious experiences" in M.Velmans (ed) op cit.) I ask, "Where does one point, when one points at consciousness"? This may seem to be an odd question. But it is an important one. If one does not know how to pick out what one is investigating, how can one investigate it? In the context of current Dualist vs Reductionist debates, my suggested route through this is a radical one - although I argue that it is completely consistent both with science and with common-sense. Ultimately, it leads to a reflexive, nonreductionist science of consciousness.

Extract:

"What is consciousness?

At first glance this looks like an easy question, as consciousness is something that we all have. However, no question has been the subject of greater confusion. In Velmans (1996 - this volume) I have argued that definitions need not be final for research to get under way. It is enough that definitions are sufficiently similar for different investigators to be able to agree that they are investigating the same thing. As science begins to unravel the causes of consciousness, the functions of consciousness, how consciousness relates to nonconscious processing and so on, our understanding of what consciousness is will deepen - for the reason that such relationships form part of the meaning of the term (its connotative meaning, or sense). Such mutual focusing of attention followed by exploration of the nature of what is attended to (and how it relates to other things) is fundamental to how phenomena come to be understood in a socially shared way. In this respect, coming to understand the nature of consciousness is no different to coming to understand the nature of anything else.

Of course, to learn what something is, it is useful in the initial instance to know where it is, so that one can point to it - enabling the attention of different investigators to be focused upon it. But where does one point, when one is pointing at consciousness?

Where dualists and reductionists think consciousness to be. According to Descartes the material world is composed of res extensa, a substance that has both location and extension in space. Consciousness is formed out of res cogitans a substance which thinks, but which has no location or extension in space. If this is right, then one cannot point at consciousness as it has no location. At best, one might be able to point at the place where consciousness interfaces with the material world. According to Descartes this is at the pineal gland located in the centre of the brain.

Modern reductionist philosophers (e.g. Dennett 1991; Searle 1993) argue that consciousness is nothing more than a state or function of the brain. It might be difficult to point with any precision at such states or functions as they are likely to be distributed properties of large neuronal populations (cf Dennett & Kinsbourne 1992). Nevertheless, if one had to point one would point at the brain.

In short, classical dualists and reductionists disagree vehemently about what conscious is, but they agree (roughly) about where it is. In so far as consciousness can be located at all, that location is somewhere in the brain.

A common-sense view of consciousness. In Velmans (1990, 1993a) I have argued that this currently popular view has no basis either in science or in everyday experience. In order to decide where consciousness is (or whether it has any location) one has to attend to its actual phenomenology. It is true that there are some experiences which seem to be poorly localized in space, or at best localized somewhere in the head or brain, just as dualists and reductionists claim. Examples include thoughts and vague feelings such as the verbal thoughts, feelings of understanding and so on which accompany reading (as described above). However, most experiences have a very different phenomenology, for example experiences of the body or of the external world.

Let me illustrate with a very simple example. Suppose you stick a pin in your finger and experience a sharp pain. Within philosophy of mind pain is generally regarded as a paradigm case of a conscious, mental event. Now, where is the pain? Hampered by their theoretical presuppositions, dualists and reductionists take this to be a rather difficult question. However, if forced to point they would point (vaguely) in the direction of the brain (see comments by Nagel, Harnad, Searle, Marcel, and Dennett, following Velmans 1993a). I take this to be a very simple question. The pain one experiences is in the finger. If one had to point at it one should point at where the pin went in. Any reader in doubt on this issue might like to try it.

Let me be clear that this sharp difference of opinion is about the experience of pain and not about the antecedent physical causes (the deformation and damage to the skin produced by the pin) nor about the neural causes and correlates of pain. The proximal neural causes and correlates of pain are undoubtedly located in the brain. However, in science, the causes or correlates of a given event are not ontologically identical to that event. For example, the movement of a wire through a magnetic field causes an electrical current to flow through the wire. But that does not mean that the electrical current is ontologically identical to the movement of the wire through the magnetic field. Nor, if one reverses this experiment, is it right to say that the current one passes through a wire is ontologically identical to the surrounding magnetic field produced as a result.

The current is in the wire and the magnetic field is distributed in the space around the wire. They cannot be the same thing for the reason that they are in different places. Similarly, innervation of appropriate pain circuitry in the brain may cause an experience of pain in the finger. These cannot be the same thing because they are in different places.

No, I am not being facetious. This simple example demonstrates a general principle which leads one away from both dualism and reductionism towards a "reflexive" model of how consciousness relates to the brain and the physical world (cf Velmans 1990). In many respects, there is no difference between these theoretical positions. For example, dualism, reductionism and the reflexive model agree that there may be physical and neurophysiological causes and correlates of a given experience within the brain - and that we can leave it to science to discover what these are (the so-called "easy questions"). But they disagree about the nature and location of the effects (the resulting experiences). Dualists claim that experiences have no location or extension in space (although they interface with the brain). Reductionists claim that all experiences are in the brain. The reflexive model claims that experiences are where we experience them to be. If the pain seems to be in the finger then that is where the pain is. There is no other or second experience of pain in the brain, or 'nowhere' to point at. This, I submit, is common sense.

But is this consistent with science? In the reflexive model the sequence of events in perception (in highly simplified form) is as follows. An input stimulus activates peripheral and central nervous system activity to produce a representation of that stimulus in the brain of a subject (S). S's brain encodes the properties of the stimulus, which for exteroceptive stimuli and many interoceptive stimuli will include its location and extension in three-dimensional space. A mental model of the stimulus is formed which may be influenced by previous experiences stored in memory, by expectations and so on. From the third-person perspective of an external observer (E), the mental model in S's brain appears to take a neural or other physical form. Indeed, from the perspective of E, this is all that can be observed of S's representation of the input stimulus, as E cannot observe S's experience of the stimulus.

If S had no experience of the stimulus, E's description of S's perceptual processing in terms of peripheral and central nervous system activity might now be complete. Indeed in functional terms there might be nothing to distinguish S's perceptual processing from that of a nonconscious robot designed to emulate such processing.

But, if appropriate conditions are met (if the stimulus is supra-threshold, if it is attended to, etc.) S does have an experience. The form that the experience takes is determined by the way the input stimulus is modelled by the brain, but it is the result or conclusion of the modelling process that is manifest in S's experience. One aspect of such modelling is judging where things are. Consequently, damage to S's finger is represented both in his resulting mental model and in his consequent experience (accurately) as an event taking place in his finger. Damage to S's finger is not manifest in his experience as a pain in the brain.

In sum, damage to S's finger ends up as a pain in his finger. That is why the entire process is "reflexive." If S pricks his finger with a pin, there is only one experience of pain that results - the pain that he experiences in his finger. E has no access to S's experience, so he has no evidence that S is mistaken about where his pain is. On the contrary, E can easily confirm S's report by sticking a pin into his own finger. In this way, the observation that sticking a pin in a finger produces pain in the finger is intersubjective and repeatable (thereby fulfilling the basic conditions for scientific investigation of this phenomenon - see Velmans 1993a). Given this, why do many philosophers and scientists currently insist that the pain must be in the brain?

One reason has to do with the dominance of the third-person perspective in science - which can be caricaturised as, "If you can't see it from the outside it doesn't exist!" This was the driving force behind the now discredited behaviourist approach to psychology. And it persists in a more sophisticated form in current, reductionist philosophies of mind. If one views the brain from the outside one can only observe brain states, not conscious experiences. Consequently, they argue, in so far as conscious experiences exist they must be brain states and must therefore be in the brain. In essence, this approach attempts to reduce what is observed from a subject's first-person perspective to what can be observed from an external observer's third-person perspective. Reductionist philosophers accept that this seems to conflict with common sense (conscious experiences seem very different to brain states) but they maintain that one day, science will discover these to be one and the same.

Needless to say, no such discovery has yet been made. Given this, reductionist philosophers have had to content themselves with trying to show what kind of discovery could show experiences and brain states to be one and the same. I will not review these arguments in detail, as my aim is to present an approach that is consistent with science and common sense. Commonly, however, reductionists argue that if science manages to discover the neural causes of consciousness and can consequently explain the occurrence of consciousness in neural terms then consciousness will have been shown to be nothing more than a state of the brain (see, for example, Place 1956, Churchland 1988).

The counterargument to this is that causes are not ontologically identical to their effects (see the discussion of electricity and magnetism above). Penfield & Rassmussen (1950), for example, caused their patients to have somatosensory experiences by direct electrical stimulation of the somatosensory cortex via microelectrodes. However, this resulted in sensations of numbness and tingling in different regions of the body, not in the brain. In any case, nearly all theories of the consciousness-brain relationship accept that antecedent neural causes of given conscious experiences can in principle be found, whilst retaining very different views about the nature of the effects (the conscious experiences that result). This is true, for example, for interactionist dualism (which assumes a two-way causal interaction of consciousness with the brain), epiphenomenalism (which assumes that brain states cause conscious experiences but not vice versa), and emergent interactionism (which assumes that consciousness emerges from brain activity and then supervenes over the activity from which it emerges). The reflexive model also urges scientific investigation of the neural and psychological causes of given experiences. But a pin in the finger still produces a pain in the finger, not a pain in the brain.

One might of course ask how, if the neural causes and correlates of pain are in the brain, does the resulting experience of pain get to be in the finger? This is a scientific question rather than a philosophical one, roughly analogous to well-known puzzles in science like how is action at a distance possible (in gravity) how can remote events remain connected (Bell's theorem in quantum mechanics) and so on. In such instances, we simply have to accept, given the evidence, that such things take place and get on with examining the detailed conditions under which they take place. The main difference in the case of pain localisation is that a psychological process rather than a physical process is involved. In Velmans (1990) I have called this process "perceptual projection."

The experience of pain in the finger is initiated by stimulation of the afferent pain fibres which terminate there. But perceptual projection of pain to the finger cannot be explained by this purely physical connection - for, if the entire arm is severed from the body, pain may be still be experienced in the now, nonexistent hand of a "phantom limb"!

Livingston (1943) for example, reports that

"In 1926, a physician, who had long been a close friend of mine, lost his left arm as a result of gas bacillus infection ... The arm was removed by a guillotine type of amputation close to the shoulder and for some weeks the wound bubbled gas. It was slow in healing and the stump remained cold, clammy, and sensitive ... In spite of my close acquaintance with this man, I was not given a clear impression of his sufferings until a few years after the amputation, because he was reluctant to confide to anyone the sensory experiences he was undergoing. He had the impression, that is so commonly shared by layman and physician alike, that because the arm was gone, any sensations ascribed to it must be imaginary. Most of his complaints were ascribed to his absent hand. It seemed to be in a tight posture with the fingers pressed closely over the thumb and the wrist sharply flexed. By no effort of will could he move any part of the hand ... The sense of tenseness in the hand was unbearable at times, especially when the stump was exposed to cold or had been bumped. Not infrequently he had a sensation as if a sharp scalpel was being driven repeatedly, deep into ... the site of his original puncture wound. Sometimes he had a boring sensation in the bones of the index finger. The sensation seemed to start at the tip of the finger and ascend the extremity to the shoulder, at which time the stump would begin a sudden series of clonic contractions. He was frequently nauseated when the pain was at its height. As the pain gradually faded, the sense of tenseness in the hand eased somewhat, but never in a sufficient degree to permit it to be moved. In the intervals between the sharper attacks of pain, he experienced a persistent burning in the hand. The sensation was not unbearable and at times he could be diverted so as to forget it for short intervals. When it became annoying, a hot towel thrown over his shoulder or a drink of whisky gave him partial relief". (cited in Melzack, 1973)

Phantom limbs also demonstrate that perceptual projection is not confined to experiences of pain. Melzack (1973) in his review of phantom limb experiences, reports that -

"Most amputees report feeling a phantom limb almost immediately after amputation of an arm or a leg.....The phantom limb is usually described as having a tingling feeling and a definite shape that resembles the real limb before amputation. It is reported to move through space in much the same way as the normal limb would move when the person walks, sits down, or stretches out on a bed. At first, the phantom limb feels perfectly normal in size and shape - so much that the amputee may reach out for objects with the phantom hand, or try to get out of bed by stepping onto the floor with the phantom leg. As time passes, however, the phantom limb begins to change shape. The arm or leg becomes less distinct and may fade away altogether, so that the phantom hand or foot seems to be hanging in mid-air.

Sometimes the limb is slowly 'telescoped' unto the stump until only the hand or foot remain at the stump tip".

In addition to such tingling and kinaesthetic sensations, amputees report a variety of other sensations including pins-and-needles, itching, sweating, warmth or coldness and heaviness in their phantom limbs (Melzack, 1973; Craig, 1978).

Such evidence supports the view that the experienced body, including its experienced location and extension in space is, in part, a construction formed by mental modelling within the brain. In Velmans (1990) I review evidence that similar constructive processes involving perceptual projection take place in normal exteroception, that is, in audition and vision. I will not repeat that review here. Suffice it to say that in audition, the proximal stimulus is vibration at the eardrum, but sounds are generally experienced to be localised in the space beyond the body surface, not at the surface of the eardrum or in the brain. The factors which govern spatial localisation in audition have been extensively investigated (cf Blauert 1983). In vision, the factors which govern the perceived size, shape, location and movement of objects in space have been investigated in many different ways. Of particular relevance to the study of perceptual projection are the varied demonstrations of how information arranged on a two-dimensional surface may under appropriate circumstances be interpreted by the brain to have arisen from a three-dimensional scene, resulting in the two-dimensional information being experienced as objects and events in three-dimensional space. Recent examples include holograms, and virtual realities. Another recent demonstration is provided by stereoscopic pictures (Figure 1), a development of the random-dot stereograms initially developed by Julesz (1971) to investigate depth perception. Some of these appear, on first glance, to be multicoloured, random patterns on a two-dimensional surface. However if one focuses one's gaze behind the surface, the random patterns gradually form into shapes arranged in three-dimensional space. What is particularly striking about such pictures is that the transition from a two-dimensional pattern to three-dimensional shapes occurs sufficiently slowly to experience perceptual projection in action.

Figure 1 (not included)

Figure 1. A stereoscopic picture of "snowflakes." To experience the picture in depth, bring the picture up to your nose and look through it, so that the picture is completely blurred. Now leaving your eyes relaxed and looking through the picture, gradually move the picture away to a distance of a foot or more, and a three-dimensional scene should form. Notice that once an experienced three-dimensional scene is formed it is possible to inspect different parts of it without losing the experience of depth. This is an example of "perceptual projection" in action, demonstrating the brain's ability to create an experience of depth, in spite of the fact that the cues are arranged on a two-dimensional surface. "Snowflakes" is reproduced with permission from 3D Magic, taken from the 3D Magic Portfolio, published by Dragon's World.

In Velmans (1990, 1993a) I suggest that such demonstrations of perceptual projection exemplify the operation of normal exteroceptive and interoceptive processing. Of course, not all experiences are given a clear location or extension in space. For example, experienced thoughts and other "inner" experiences such as visual images, vague feelings and so on, represent the ongoing results of problem solving, planning and other cognitive and conative activities taking place within the brain itself. Consequently, in so far as these "inner" experiences have any location, they are (loosely) experienced to be within the head or brain. As before, mental modelling places such events more or less where they actually are. By contrast, events which originate in the body or beyond the body surface, once modelled by the brain, are reflexively projected in the form of experienced events within the body or beyond the body surface. Such inner, body, and external experiences together form the contents of consciousness, which are none-other than the contents of our everyday phenomenal world. We normally call some aspects of this phenomenal world the "physical world" (the experienced body and its experienced surround). But the appearance of such "physical" entities and events remains, in part, a construct of the brain. The appearance represents the entities and events which are detected by the sense organs in a biologically useful way, but it is not identical to those entities and events (the "things-themselves"). Physics, for example, would represent the same entities and events in a very different way (in terms of relativity, quantum mechanics, and so on).

To those accustomed to thinking in a dualist or reductionist way the claim that the phenomenal world includes what we normally think of as the "physical world" may seem odd. But note that this is entirely consistent with what we actually experience. With our eyes open, we experience a phenomenal world spread out before us in space, not a world in the brain (or without any location). Nor is this way of looking at things new. The view that the phenomenal world is a representation constructed by the mind, is central to the philosophy of Immanuel Kant (1781), along with the separation of the phenomenal world from some grounding reality (the "thing-itself"). The extension of consciousness to include the external world as-experienced occurs also in the work of Ernst Mach (1885), William James (1890), Alfred North Whitehead (1932), and Bertrand Russell (1948), as well as in the scientific theorising of Charles Sherrington (1942), Wolfgang Kohler (1966), and Karl Pribram (1979). It is also a basic assumption of phenomenology (cf Spinelli 1989). Needless to say, different theorists have argued for this position in different ways, and their opinions about the consequences also differ.

The reflexive model gives an account of how consciousness relates to the brain and the physical world which is neither dualist nor reductionist. Experiences arise from a reflexive interaction of initiating stimuli with perceptual processing. This interaction results in an experienced, phenomenal world which includes what we normally think of as the "physical world." That is, what we normally think of as the physical world is part-of what we consciously experience; it is not apart-from it. If so, there can be no unbridgeable divide separating the contents or "qualia" of consciousness from experienced physical phenomena.

This has many interesting consequences for the dualist vs reductionist debate within philosophy of mind, the issue of realism vs idealism, and the relation of psychology to physics. These have been discussed in Velmans (1990, 1993a). Initial attempts have also been made to challenge aspects of the model (see Gillett 1992; Rentoul 1992; Wetherick 1992 - and the replies by Velmans 1992a,b; see also the discussion with Marcel, Nagel, Gray, Searle, Libet, Humphrey, Wall, Lockwood, Shevrin, and Dennett, following Velmans 1993a). I do not have space to recount these discussions here. In what follows I deal only with some of the main implications of the reflexive model for psychological science.

1. The most obvious advantage of the reflexive model is its ecological validity. We experience the phenomenal world to be outside our heads. We do not experience this world to be inside our brains. Having a model which reflects what we actually experience, encourages exploration of how it comes to be that way. For example, it encourages the study of perceived spatial localization and extension, and in particular the mechanisms underlying perceptual projection. It also encourages the study of how perceptual processes in the brain combine to produce an integrated, three-dimensional, phenomenal world.

2. The model potentially enables a more unified understanding of a wide range of phenomena experienced to have both spatial location and extension, including phenomena as diverse as lucid dreams, hallucinations, eidetic imagery, the creation of virtual realities, the construction of a body-image, and the normal perception of events in a three-dimensional space. Accepting perceptual projection as a normal process (when it operates on representations of events out in the world) also makes it easier to understand what happens in pathological or artificial situations. For example, hallucinations can be understood to result from mental models which are erroneously subject to perceptual projection (following a breakdown of the usually reliable modelling of "inner" versus "external" events). And three-dimensional virtual realities can be understood to arise from artificial stimulation of the same projective processes which create normal, phenomenal worlds.

It should be clear from the reviews in this book that a science of consciousness is possible, as it is actual and flourishing. But it has often been claimed that the study of consciousness can never be a proper science, as consciousness and its contents have characteristics that are quite unlike the natural world. These assumptions about consciousness still persist.

Consider, for example, the situation depicted in Figure 2, in which a subject (S) is asked to focus on a stimulus (say a cat) while an experimenter (E) tries to observe what is going on in the subject's brain. E has access to S's brain states but has no access to what S experiences. Other experimenters can also access S's brain states. Consequently, what E has access to is thought of as "public" and "objective." S's experiences, by contrast, are considered to be "private" and "subjective." If so, how could S's experiences provide a data-base for science?

Figure 2. A Reflexive Model of the causal sequence in visual perception. Light rays from a cat (as perceived by an experimenter E) impinge on the eye of a subject S. Impulses travelling up the optic nerve produce neural representations of the cat within S's central nervous system. Information within this neural representation is formed into an "experiential model" of the cat, that is into the cat as-perceived by S. To S, the cat as-perceived is out in the world, not in his head or brain. In this, the cat that S experiences is similar to the cat that E experiences, although it is viewed from the perspective of S rather than the perspective of E. In short, an event in the world is experienced to be in the world, which makes the causal sequence reflexive (from Velmans 1990).

Note that this radical difference in status of the data accessible to E and S is enshrined in the very words we use to describe what they perceive. That is, E makes "observations," whereas S merely has "subjective experiences." The presumed "objectivity" of E's observations and the "subjectivity" of S's experiences also motivates reductionism in current philosophy of mind (for example, attempts to demonstrate that S's experiences are nothing more than the brain states observed by E).

But the reflexive model gives a very different story. According to the model, both E and S inhabit phenomenal worlds which are each, in a sense, private to themselves. E and S are no different in this respect to you and me. I cannot access your experienced world and you cannot access mine. In the situation depicted in Figure 2, E's private phenomenal world includes the events he observes in S's brain, while S's private phenomenal world includes the cat.

It is true that other experimenters (E1 to En) could also focus their attention on the events in S's brain and observe what E observes. In this way, their observations may become "public" in the sense of being communally shared. However, each observation remains private to a given experimenter. When the observations made by different experimenters are sufficiently similar, they become "intersubjective"; if they can be made on more than one occasion they also become "repeatable" (cf Velmans 1993a). But it is equally true that other subjects (S1 to Sn) could focus their attention on the cat and observe what S observes. In this sense, what S observes can also be made "public," "intersubjective," and "repeatable."

Note that this does not apply only to observed cats but also to less tangible experiences such as images and pains. For example, S1 to Sn might all report that a pin in the finger produces a pain in the finger, or that a dose of aspirin reduces the pain. The fact that staring at a red spot produces a green after-image is similarly "public," "intersubjective," and "repeatable." In short, there is nothing intrinsic about the epistemic status of E's observations which distinguishes them from those of S.

The same principle can be illustrated in another way by asking E and S to turn their heads, so that E switches his attention to the cat, while S switches his attention to what is going on in E's brain. In this situation, E becomes the "subject" and S becomes the "experimenter." Following current conventions, S would now be entitled to think of his observations (of E's brain) as "public and objective" and to regard E's observations of the cat as "private and subjective." But this outcome is absurd - as nothing has changed in the character of the observations of E and S other than the focus of their attention.

In sum, the effect of this analysis is to remove the pretence that observations have nothing to do with the "conscious experiences" of observers, and that E's observations are "objective" while S's experiences are "subjective." Either E or S can make observations that are objective in the sense of being dispassionate, truthful and so on. But neither E nor S can make observations that are objective in the sense of having nothing to do with what they experience. Both E and S observe or experience phenomenal worlds, which arise from a reflexive interaction of attended-to entities and events with perceptual processes. What E or S observe depends entirely on their focus of attention.

There is a good deal more to be said about the implications of the reflexive model for the relation of "public" to "private" events, and for "subjectivity", "intersubjectivity" and "objectivity" (cf Velmans 1993a). It should also be stressed that I have given a very simplified analysis of the basic procedures involved in the study of conscious experiences. The contents of consciousness vary greatly in their stability, repeatability, reportability, measurability, and so on. Consequently, the methods appropriate to investigating such phenomena also vary.

But it should be clear that the reflexive model gives quite a different view about whether the study of the phenomena that we experience can ever be a science. If the above analysis is correct, the "phenomena" observed by experimenters are as much a part of the world that they experience as are the "subjective experiences" of subjects. If so, the whole of science may be thought of as an attempt to make sense of the phenomena that we observe or experience.

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