Velmans, Max (1995) The Limits of Neurophysiological Models of Consciousness.  Behavioral and Brain Sciences, 18 (4), 702-703
(commentary on Gray, J. (1995) The contents of consciousness: a neurophysiological conjecture. BBS, 18 (4): 659-676).
Copyright Cambridge University Press 



(commentary on Gray, J. (1995) The contents of consciousness: a neurophysiological conjecture. BBS, 18 (4): 659-676).

Max Velmans
Department of Psychology
University of London
Lewisham Way
SE14 6NW


ABSTRACT. This commentary elaborates on Gray's conclusion that his neurophysiological model of consciousness might explain how consciousness arises from the brain, but does not address how consciousness evolved, affects behaviour or confers survival value. The commentary argues that such limitations apply to all neurophysiological or other third-person perspective models. To approach such questions the first-person nature of consciousness needs to be taken seriously in combination with third-person models of the brain. 

KEYWORDS: consciousness, functionalism, evolution, first person, third person, reductionism, neurophysiological models


What would a theory of consciousness need to explain? According to Gray it would need to explain (1) how consciousness evolved, (2) how it confers survival value (3) how it arises out of brain events, and (4) how it alters behaviour (introduction, para 5). Much of Gray's target article deals with question 3, focusing both on how consciousness relates to the neurophysiological structure of the brain and to the brain viewed as an information processing system. The research literature in this area is extensive (cf Farthing 1992, and reviews in Velmans 1996) - but Gray's closely-argued attempt to relate consciousness to the output of a subicular comparator approaches the issues from an unusual direction in that it draws on the blocking of latent inhibition in laboratory rats and studies of schizophrenia in humans, whereas it is more common in this area to draw on experimentally induced contrasts between conscious and pre- or nonconscious processing in normally functioning human adults (cf Baars 1988; Velmans 1991) or on clinical dissociations between consciousness and nonconscious functioning within neuropsychology (cf readings in Milner & Rugg 1992).

Gray's conclusions about the kind of information processing that might support consciousness nevertheless converge in some respects with those of other theorists. It is generally accepted, for example, that any theory which relates consciousness to human information processing needs to deal not only with the diversity of the contents of consciousness, but also with how those diverse contents are constructed into a coherent experience, already integrated, assessed for its novelty or importance, and served up in a way that enables adaptive interaction with the world. Whether this is achieved primarily by a "comparator system," as Gray suggests, or best thought of in another way depends heavily on the experimental phenomena one seeks to explain. Students of preconscious versus conscious input analysis, for example, usually allocate such functions to either "pre-attentive" or "focal-attentive" processing, whereas those concerned with conscious versus nonconscious control of action tend to speak of a central "executive," "monitoring," or "control" system. Gray's suggestion that input stimuli take around 50ms to become conscious (sect. 5.3) is also debatable, as there is converging evidence that the first 200 ms or so of input processing is preconscious, which would allow time for analysis, identification, selection and integration of attended-to input before they enter consciousness (Posner & Snyder 1975; Neeley 1977; Libet 1993). Many would also take issue with Gray's association of consciousness with neurophysiological activity in a fixed location. But I will leave the fuller discussion of such details to other commentators - and turn to the wider issues.

Although the bulk of Gray's article is concerned with neurophysiological modelling, he has a fine grasp of the limits of neurophysiological accounts of consciousness. As he notes (sect. 4) biological forms are embodied in physicochemical processes, but the evolution of biological forms cannot be fully understood in terms of physics or chemistry. Rather, the combinatorial options in the genetic code have a syntax and semantics that can only be understood in terms of selection by consequences, following biological laws of Darwinian survival and Mendelian genetics. In similar fashion, emergent patterns of neural activity can only be understood in terms of their wider adaptive consequences. The syntax and semantics of language, for example, may be embodied in neurophysiological activity, but can only be understood in terms of the constraints required for successful communication between individuals. In short there is a un-mysterious sense in which genetics does not reduce to chemistry and the higher-order patterning of neural activity does not reduce to neurophysiology.

But in what way do such emergent properties relate to consciousness? As Gray notes, one can give "a perfectly good materialist account of brain events, whether considered under a physicochemical or a syntactic (computational) description ... without recourse to the hypothesis of consciousness." The main reason for bringing in consciousness is because it is there (sect. 4, para 6). However, he argues, there is one further level of organization in the brain which is the same as the level of conscious experience. At this level, "the semantically interpreted content of representations plays a causal role in the unfolding of events." Following Pylyshyn (1984) such semantically interpreted content is also "cognitively penetrable." As with other levels of organization, this "conscious" level does not reduce to lower levels, but again for un-mysterious reasons.

However, there are difficulties in linking consciousness exclusively to cognitive penetrability, as this would imply that sensations which are not cognitively penetrable (alterable by cognition) are not conscious - which would seem to rule out bee-stings, the smell of camphor, and the roar of a jet engine. But these sensations clearly are conscious. And there is a more fundamental problem: even if there were a distinct level of neural organization to which consciousness corresponds, one would not need to refer to consciousness to explain that organization. Cognitive-penetrability, for example, can be explained in information processing terms, without reference to consciousness. In short, although Gray comes closer than most other theorists to accepting the sense in which consciousness seems to be tangential to information processing or neural accounts, he shies away from the logical conclusion that it is tangential to such accounts (cf Velmans 1991).

The reasons, of course, have do with the "dire" theoretical consequences. The attempt to relate consciousness to neurophysiological activity or information processing in the brain is unquestionably important for the reason that this will eventually reveal something about the necessary and sufficient conditions (within the brain) for conscious experience, thereby providing an answer to question 3. But if we can explain how such processing fulfils its adaptive purposes without reference to consciousness we would seem to be in trouble with questions 1, 2, and 4. And this would produce an awkward gap in evolutionary theory. Gray is acutely aware of the problem. As he notes, "if consciousness is a product of Darwinian evolution, it must confer survival value and therefore must affect behaviour." Rather than abandon this biological perspective he proposes to search on for what this influence might be (sect. 6).

In Velmans (1991) I suggest that the function to which consciousness is most closely linked is information dissemination, a late-arising stage of focal-attentive processing which enables the brain to respond to the most pertinent, selected information in an integrated way. Absence of information dissemination produces dissociations of functioning, for example, in blindsight (where part of the system has the ability to make visual discriminations but the system as a whole does not "know that it knows"). Similar proposals have been made by Baars (1988), Navon (1991) and Van Gulick (1991). However, even if this were the most closely associated function the problem outlined above would not go away. Information dissemination, like cognitive penetrability can be explained in purely information processing terms without reference to consciousness - and the same would be true of any function that can be described in information processing terms. If so, a prolonged search for consciousness within an information processing model of the brain is doomed to failure.

Yet, as Gray rightly points out, consciousness exists - and there are aspects of consciousness (qualia, what it is like to be something, how things appear from a first-person perspective) that do not seem reducible to either a physical or functional state of the brain (see discussions between Dennett, Fenwick, Gray, Harnad, Humphrey, Libet, Lockwood, Marcel, Nagel, Searle, Shoemaker, Singer, Van Gulick, Velmans, and Williams in Marsh, 1993). Given this, it is time for radical measures.

My suggestion is that we should stop trying to reduce consciousness to a physical or functional state of the brain and start to take consciousness in the form that we normally experience it seriously. That is, we need to reincorporate the first-person perspective into psychological science in order that we may properly come to understand its relation to traditional third-person perspective science. There are many arguments in favour of this, and the consequences which follow for our understanding of how consciousness relates to the brain and physical world are radical. I cannot go into these matters in the limited space available for commentaries (but see Velmans 1990, 1991, 1993a, 1993b). In passing, however, it is interesting to note that Gray's questions 1, 2, and 4 which seem to be unapproachable from a purely third-person perspective seem to be more tractable when they are simultaneously approached from a first-person perspective. For example, if one accepts that given conscious states have correlates which (viewed from a third-person perspective) take the form of given neural representational states, then as neural representations evolve, their conscious correlates will also evolve (question 1). From a first-person perspective, what we perceive, think, feel and so on has obvious effects on what we do - that is, conscious states alter behaviour in an indefinitely large number of ways (question 4). From a first-person perspective consciousness also has an obvious "survival value" for without it, few human beings would wish to survive (question 2). How such first-person facts relate to some expanded evolutionary theory presents a new challenge for science.

Kuhn (1970) has described normal science as a strenuous and devoted attempt to forced nature into the conceptual boxes supplied by the existing paradigm. Our understanding of consciousness has been blocked by the attempt to squeeze its manifest first-person nature into a third-person information processing model of the brain. It is time for the squeezing to stop.

Additional references.(to those in the target article)

Kuhn, T.S.(1970) The structure of scientific revolutions. University of Chicago Press.

Milner, A.D. & Rugg, M.D. (eds.) (1992) The neuropsychology of consciousness. Academic Press.

Navon, D.(1991) The function of consciousness or of information?

Behavioral and Brain Sciences 14(4):690-691.

Neely, J.H.(1977) Semantic priming and retrieval from lexical memory: Roles of inhibitionless spreading activation and limited capacity attention. Journal of Experimental Psychology: General 106:226-254.

Posner, M.I. & Snyder, C.R.R.(1975) Facilitation and inhibition in the processing of signals. In: Attention and Performance V. eds. P.M.A. Rabbitt & S. Dornick. Academic Press.

Van Gulick, R.(1991) Consciousness may still have a processing role to play. Behavioral and Brain Sciences 14(4):699-700.

Velmans, M.(1990) Consciousness, brain, and the physical world. Philosophical Psychology 3(1):77-99.

Velmans, M.(1993a) A reflexive science of consciousness. In Experimental and theoretical studies of consciousness ed. J Marsh. Ciba Foundation Symposium No.174. Wiley, Chichester.

Velmans, M.(1993b) Consciousness, causality, and complementarity. Behavioral and Brain Sciences 16(2):404-416.

Velmans, M. (ed) (1996) The Science of Consciousness: Psychological, neuropsychological and clinical reviews. Routledge, London (in press).