consciousness

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The twentieth-century British psychologist Stuart Sutherland once defined consciousness as ‘a fascinating but elusive phenomenon: it is impossible to specify what it is, what it does, or why it evolved. Nothing worth reading has been written about it.’ Consciousness is indeed hard to define, but most people have an intuitive idea of what it is. It encompasses two different concepts: the notion of a self, and the feelings of which the self is aware, especially qualia — our raw sensory experiences.

Although some philosophers (panpsychists) have believed that all things, including inanimate objects such as chairs and umbrellas, are conscious, most people agree that consciousness is associated with brains (and, some would argue, with inanimate machines that work, in some crucial respect, like brains). Stated simply, then, the problem is how does the activity of nerve cells in the brain give rise to our subjective mental life? Neurons — specks of jelly in the brain, with their electrical impulses and their little squirts of neurotransmitter — seem so utterly different from the redness of red or the flavour of Marmite on toast.

The riddle of qualia is best illustrated with a thought experiment. Imagine a neuroscientist in some future century, who has complete knowledge of the workings of the brain — including the mechanisms of colour vision — but who happens to be colour blind and cannot herself distinguish between red and green. She uses the latest scanning techniques to generate a total description of all the electrical and chemical events in the brain of a normal human as he looks at a red object. The functional account may seem complete, but how could it be so without an explanation of the nature of the unique experience of red, which the scientist herself has never had? There is a deep epistemological gulf between descriptions of physical events in the brain and the personal, subjective experiences that we presume to be associated with those events.

Is consciousness a property of the entire brain — does it ‘emerge’ when the brain reaches a certain level of complexity? Or are only some parts of the brain conscious? (After all, if we argue that only brains and not other organs are conscious, why not imagine that only some parts of the brain are involved?) Indeed, neurological evidence suggests that we are unconscious of most of the activity in our brains — not just the below-stairs business of running the heart, digestion, posture, and so on, but also the pre-perceptual processing of information from the senses, and the complex task of selecting and controlling the individual muscles that carry out actions.

A rare disorder, aptly called ‘blindsight’, strikingly demonstrates a dissociation between conscious and unconscious visual processing. It results from damage restricted to the primary visual cortex in the cerebral hemispheres, which classically causes ‘cortical blindness’ in a corresponding part of the visual field. Although the patient denies seeing, say, a small spot of light presented in the blind part of the field, he or she can fairly accurately point towards the spot. Moreover, if a moving spot or a line is shown, the patient can ‘guess’ the direction of movement or the angle of the line, all the time unaware that it exists! This amazing paradox is explained by the fact that there are two main pathways of interconnected nerve cells from the eyes and through the brain. One goes to the primary visual cortex, and on into the lower parts of the temporal lobe, which is responsible for the identification of objects and the laying down of personal memories. The other projects via the reflex visual centres of the midbrain (which control eye movements) and thence up to the parietal lobes of the cortex, where the information is used to guide hand movements. Since the latter pathway is still intact in the patient with blindsight, he or she can use it for reaching for the object. But the other pathway into the temporal lobe seems to be intimately involved in conscious perception. A more subtle dissociation can occur in patients who have extensive damage to the temporal lobe, which does not interfere with basic visual functions but can cause agnosia — an incapacity to distinguish consciously between different objects and shapes. However, such patients can correctly shape their hands to pick up different objects that they cannot perceptually distinguish. It is almost as though there is an unconscious ‘zombie’ inside the heads of such patients, ‘seeing’ the world and guiding the hands but not troubling consciousness with what it is doing.

Unconscious vision is not just a neurological anomaly — it occurs even in normal people. If you are driving a car while talking to the person next to you or on a mobile telephone, many parts of your brain are processing enormous amounts of visual information to enable you to negotiate the traffic. Yet little of it reaches consciousness so long as your attention is focused on the conversation. Interestingly, it is hard to imagine the opposite scenario — of having a conversation unconsciously while paying attention to the traffic. At any instant, we seem to be fully aware of only a minute fraction of the things that we could be aware of. As you stand chatting to a friend at a party, you are unaware of the content of the other conversations around you — unless you deliberately eavesdrop out of the ‘corner of your ear’. Equally, our embarrassingly poor ability to recall the detail of a visual scene if the lights are suddenly switched off indicates that we are genuinely aware of only a tiny fraction of the flood of information that pours into our brains from our eyes. Only the focus of current attention seems fully represented in our consciousness, in the sense that it can be remembered. This all suggests that there is a link between consciousness, attention, and memory, and also that we cannot use language creatively without being conscious.

This raises the so-called ‘Zombie problem’. If we are able to do so much without being aware of it, what purpose does consciousness serve, and how did it evolve? Imagine an unconscious zombie that looks exactly like a person and does all the things a conscious human does, but without being conscious. There seems to be nothing logically impossible about this. Indeed, we have no way of knowing, for sure, that machines, animals, or even other human beings are truly conscious in the way that we feel ourselves to be. Some philosophers, most notably Gilbert Ryle, have argued that concepts of mind, such as self and intention, are merely ‘category mistakes’ — muddles that arise from the misuse of language. Such virtuosic philosophical argument reinforces the ‘Zombie problem’, but is deeply unsatisfactory. We know that we are conscious. Indeed, as René Déscartes pointed out, knowing that we are aware is the only thing that we are really sure about — ‘cogito, ergo sum’.

In parallel with Ryle's attempt to explain away the ‘Ghost in the Machine’, the school of psychology called behaviourism also argued that consciousness does not (or need not) exist and that science should confine itself to an attempt to explain externally observable behaviour. To behavioural psychologists, it has indeed been valuable to view the brain objectively, merely seeking accounts of behaviour without the baggage of common-language concepts such as will, intention, and need. However, it is difficult for most people — even brain researchers — to accept the extreme notion of ‘eliminative materialism’, namely that words such as ‘love’, ‘want’, and even ‘red’ have the same logical status as the once universal but now arcane view that living things have some kind of ‘vital essence’, which distinguishes them from the inanimate world.

More intriguing is epiphenomenalism. Just as the shadow of a running horse appears to run along with it but plays no causal role in the running, consciousness may simply accompany certain brain events but not itself have a function. Can it really be true that when you feel that you are choosing to pick up a cup, it is not the conscious intention that initiates the picking up? In fact, there is growing evidence that our subjective impressions of events in the world and of our intended actions are a kind of post-hoc ‘commentary’ on things that have already happened. Disturbing though it is, our conscious lives may be a plausible but illusory tale, a translation of the zombie world into the domain of subjectivity. But why should we have such a self-deluding system in the brain? How did it evolve? What could its value be?

Faced with such philosphical conundrums, many neuroscientists, with Francis Crick as their standard-bearer, have argued that we should simply aim to define the ‘neural correlate of consciousness’ — the parts of the brain and the nature and activity of nerve cells that implement conscious states. Once we have a clear understanding of the neural activity that is both necessary and sufficient for subjectivity, perhaps many of the philosophic problems will disappear.

The pragmatic advantage of this approach is that it transforms consciousness into an empirical problem that is approachable experimentally. Instead of asking ‘What is consciousness?’, one asks ‘What parts of the brain are active, or in what special way are they active, when someone does something consciously?’ One experimental approach that is proving fruitful is to monitor the activity of different parts of the cerebral cortex (with microelectrodes in animals, or with imaging techniques in human beings) while the retinal image is unchanging but the content of consciousness changes. For instance, how does activity in the brain change as a person or animal shifts attention from one thing to another? What happens when they view ambiguous visual images that can appear, at one moment, to be one thing, but, at another instant, to be something else?

That other mysterious aspect of subjectivity — the feeling of ‘free will’ and intention — is more difficult to study. However, fingers of evidence point towards the anterior cingulate cortex, a region on the inner surface of the frontal lobe. Patients with damage here sometimes feel that their own actions occur without being intended — alien hand syndrome. Conversely, they may be fully conscious but feel that they don't want to do anything at all — akinetic mutism.

The early decades of the twenty-first century will undoubtedly see great advances in our understanding of the neural correlate of consciousness. What is less certain is whether such empirical observations will take us any closer to resolving what philosopher David Chalmers has called the ‘Hard Problem’, that is, what really is the nature of subjectivity? We may be forced to admit that consciousness, like infinity and the particle-wave concepts in quantum mechanics, is a property that cannot be made intuitively straighforward. Consciousness, like gravity, mass, and charge, may be one of the irreducible properties of the universe for which no further account is possible.

— V. S. Ramachandran, Colin Blakemore

Bibliography

• Churchland, P. M. (1996). The engine of reason, the seat of the soul. MIT Press, Cambridge MA.
• Crick, F. H. C. (1993). The astonishing hypothesis. Charles Scribner, New York.
• Ramachandran, V. S. (1998). Phantoms in the brain. William Morrow, New York.
• Searle, J. (1994). The rediscovery of the mind. MIT Press, Cambridge MA.
• Weizkrantz, L. (1986). Blindsight. Oxford University Press

See also brain; colour blindness; illusions; imaging techniques; perception; vision.

noun

The condition of being aware: awareness, cognizance, perception, sense. See knowledge/ignorance.

n

Definition: knowledge
Antonyms: senselessness, stupidity, unconsciousness

Possibly the most challenging and pervasive source of problems in the whole of philosophy. Our own consciousness seems to be the most basic fact confronting us, yet it is almost impossible to say what consciousness is. Is mine like yours? Is ours like that of animals? Might machines come to have consciousness? Is it possible for there to be disembodied consciousness? Whatever complex biological and neural processes go on backstage, it is my consciousness that provides the theatre where my experiences and thoughts have their existence, where my desires are felt and where my intentions are formed. But then how am I to conceive the ‘I’, or self that is the spectator, or at any rate the owner of this theatre? These problems together make up what is sometimes called ‘the hard problem’ of consciousness. One of the difficulties in thinking about consciousness is that the problems seem not to be scientific ones; Leibniz remarked that if we could construct a machine that could think and feel, and blow it up to the size of a mill and thus be able to examine its working parts as thoroughly as we pleased, we would still not find consciousness (Monadology, para. 17), and drew the conclusion that consciousness resides in simple subjects, not complex ones. Even if we are convinced that consciousness somehow emerges from the complexity of brain functioning, we may still feel baffled about the way the emergence takes place, or why it takes place in just the way it does.

The nature of conscious experience has been the largest single obstacle to physicalism, behaviourism, and functionalism in the philosophy of mind: these are all views that according to their opponents, can only be believed by feigning permanent anaesthesia. But many philosophers are convinced that we can divide and conquer: we may make progress not by thinking of one ‘hard’ problem, but by breaking the subject up into different skills and recognizing that rather than a single self or observer we would do better to think of a relatively undirected whirl of cerebral activity, with no inner theatre, no inner lights, and above all no inner spectator.

1. The condition of a person who is awake, rather than asleep, so that he or she is able to respond to stimuli.

2. Clinically, different levels of behaviour that can be described on a continuum from a high state of consciousness (alertness and great awareness) to a depressed state of consciousness (coma).

3. The mechanism or process by which humans are aware of sensations, elements in memory, or internal events.

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In psychology, consciousness is the subject's immediate apprehension of mental activity. Although Freud thought that conscious processes are "the same as the consciousness of the philosophers and of everyday opinion" and "a fact without parallel, which defies all explanation or description" (1940a [1938], pp. 159, 157), he argued that they could not be considered the "essence" of mental life. Rather, consciousness has a fugitive quality and does not "form unbroken sequences which are complete in themselves" (p. 157). "The psychical, whatever its nature may be, is in itself unconscious and probably similar in kind to all the other natural processes of which we have obtained knowledge" (1940b [1938], p. 283). Freud stressed, however, that consciousness still plays an importance role; indeed, it is "the one light which illuminates our path and leads us through the darkness of mental life" (p. 286).

The work of psychoanalysis, as Freud saw it, is "translating unconscious processes into conscious ones, and thus filling in the gaps in conscious perception" (p. 286). Consciousness is the qualitative perception of information arising both from the external world and from the internal world: an external world that is unknowable in itself and to which we have access only via subjective elements collected by our sense organs and an internal world that consists of unconscious mental processes and that we are aware of solely through sensations of pleasure/unpleasure and revived memories. According to Freud, "A person's own body, and above all its surface, is a place from which both external and internal perceptions may spring" (1923b, p. 25).

From the beginning Freud treated consciousness and perception as indissolubly linked, indeed, so much so that throughout his work he deemed them to constitute a single structure, the perception-consciousness system. Freud also drew a distinction, within nonconscious phenomena, between latent states susceptible of becoming conscious at any moment and repressed psychic processes inaccessible to consciousness. This led him to differentiate the unconscious system proper from a preconscious system, cut off from consciousness by censorship but also controlling access to consciousness. In this sense, the preconscious and the conscious are very close: both are governed by secondary processes and both draw on a bound form of psychic energy. In The Interpretation of Dreams (1900a), Freud spoke of the preconscious-conscious system, and in "The Unconscious" (1915e), he described the preconscious as "conscious knowledge" (p. 167), even though it provides access to unconscious contents and processes, provided that they have been transformed.

From his earliest writings on, Freud saw the link between consciousness and the ego as very close. And although by 1920 Freud viewed the ego as in large part unconscious in its defensive activities, he continued to attach consciousness to it as both the "nucleus" and the "surface of the mental apparatus" (1923b, p. 19).

By the early twenty-first century, the problem of perception had become increasingly complex. Freud's near conflation of perception and consciousness, which required him to postulate that perceptual phenomena and the laying down of memory traces are incompatible, has come in for serious reconsideration. It is worth noting, though, that Freud himself, in his last years, was given pause on this issue by the problem of fetishism, apropos of which it was apparent that perceptions and mnemic traces could be caught up in one and the same conflict. This line of thinking has led to a reevaluation of all psychopathologies where disavowal and splitting predominate, such as borderline conditions, and more generally, to a review of all states involving the relationship between perception and hallucination (see Donald W. Winnicott's notions of the subjective object and of transitionality [1953]).

Bibliography

Freud, Sigmund. (1900a). The interpretation of dreams. SE, 4-5.

——. (1915e). The unconscious. SE, 14: 166-204.

——. (1923b). The ego and the id. SE, 19: 12-59.

——. (1940a [1938]). An outline of psychoanalysis. SE, 23: 139-207.

——. (1940b [1938]). Some elementary lessons in psycho-analysis. SE, 23: 279-286.

Winnicott, Donald W. (1953). Transitional objects and transitional phenomena: A study of the first not-me possession. International Journal of Psycho-Analysis, 34, 89-97.

—RAYMOND CAHN

Michael A. Arbib
Susan Blackmore
Ned Block
David Chalmers
Paul M. Churchland
Dan Dennett
Ian Glynn
Richard L. Gregory
Nicholas Humphrey
David Papineau
Roger Penrose
Brian Pippard
Steven Rose

Michael A. Arbib

Even 'simple' mammals may be aware of the difference between feeling maternal and feeling enraged. Such 'animal awareness' seems to be part of human consciousness but the latter seems qualitatively different in nature. I argue that we are conscious in a fully human sense only because we have language. However, I deny that consciousness is merely a function of language. For example, one may have a vivid, conscious perception of a face yet be unable to put it into words. The argument of this article is further developed in Arbib (2001).

The neurological literature shows that consciousness is not a direct property of having neurons of a particular structure or complexity because the same data can be represented in two networks of comparable neural complexity, yet be accessible to consciousness only when one of the networks rather than the other is intact. In particular, clinical studies show a double dissociation between the 'declarative' ability to communicate the size of an object, whether verbally or by pantomime, and the 'procedural' ability to act upon objects (Goodale et al. 1991, Jeannerod, Decety, and Michel 1994). Since there is no data suggesting that the two regions of the brain involved in the double dissociation contain different microtubules, I think we can reject the space–time geometry view of microtubules in consciousness (Hameroff 2001). Again, since thalamocortical oscillations are equally important for the functioning of these 'conscious' and 'unconscious' regions of cerebral cortex, we must treat Llinás and Ribary's (2001) view of the role of thalamocortical oscillations with care. Perhaps we may see thalamocortical oscillations as the sign that cerebral cortex is 'powered up' into the waking state, without regarding the oscillations as themselves the 'carriers' of consciousness.

Arbib and Hesse (1986) offer a specific account of the co-evolution of human consciousness and language. There are perhaps hundreds of schemas (Arbib et al., 1998: ch. 3) active at any time to subserve the current interaction of the organism with its environment. By contrast, consciousness seems rather focused. But what is the role of consciousness? Wouldn't these schemas do their jobs just as well if there were no such thing as consciousness?

Hughlings Jackson (1878–9) viewed the brain in terms of levels of increasing evolutionary complexity. He argued that damage to a 'higher' level of the brain disinhibited 'older' brain regions from controls evolved later, to reveal evolutionarily more primitive behaviours. But the crucial point is that, once new regions are in place, they provide an enriched environment for the older parts of the brain. These now have new possibilities for further evolution.

Primitive communication subserves primitive coordination of the members of a social group and may not involve consciousness. As communication evolves, the 'instructions' that can be given to other members of the group increase in subtlety. Communication evolves at first purely as a way of coordinating the actions of a group. For this to succeed, the brain of each group member must be able not only to generate such signals, but also to integrate signals from other members of the group into its own ongoing motor planning. The key transition in going from the limited set of vocalizations used in communication by, say, vervet monkeys to the richness of human language came with a migration in time from

(i) an execution/observation matching system enabling an individual to recognize the action (as distinct from the mere movement) that another individual is making (see mirror cells), to
(ii) the individual becoming able to pantomime 'this is the action I am about to take'.

Arbib and Hesse (1986) do not emphasize the external process of 'group selection' which must have evolved in the population as a whole, but rather the changes within the individual brain made possible by the availability of a 'précis' — a gesturable representation — of intended future movements (as distinct from current movements). They use the term communication plexus for the circuits involved in generating this representation. The Jacksonian element of their analysis is the suggestion that once the brain has such a communication plexus, then a new process of evolution begins whereby the précis comes to serve not only as a basis for communication between the members of a group, but also as a resource for planning and coordination within the brain itself. This 'communication plexus' thus evolves a crucial role in schema coordination. The thesis is that it is the activity of this co-evolved process that constitutes consciousness. As such it will progress in richness along with the increased richness of communication that culminates as language in the human line.

Arbib and Hesse's thesis, then, is that it is the activity of this communication plexus that constitutes the essentially human dimension of consciousness, i.e. that 'consciousness' is defined by a neurally represented précis of potential behaviour. Such a view does not explain the phenomenology of consciousness — i.e. the way consciousness 'feels' to each of us — but it does accord well with this phenomenology. The fact that lower-level schema activity can often proceed successfully without the high-level coordination afforded by the communication plexus explains why consciousness may sometimes be active as a monitor rather than as a director of action. In other cases, the formation of the précis of schema activity plays the crucial role in determining the future course of schema activity, and thus of action — and this accords with those occasions in which we experience a conscious effort in weighing a number of courses of action before we commit ourselves to behave in a specific way.

(Published 2004)

Bibliography
• Arbib, M.A. (2001). 'Co-evolution of human consciousness and language', Annals of the New York Academy of Sciences, 929.
• — —  and Hesse, M. B. (1986). The Construction of Reality.
• — —  Érdi, P., and Szentágothai, J. (1998). Neural Organization: Structure, Function, and Dynamics.
• Goodale, M. A., Milner, A. D., Jakobson, L. S., and Carey, D. P. (1991). 'A neurological dissociation between perceiving objects and grasping them'. Nature, 349.
• Hameroff, S. (2001). 'Consciousness, the brain, and spacetime geometry'. Annals of the New York Academy of Sciences, 929.
• Jackson, J. H. (1878–9). 'On affections of speech from disease of the brain'. Brain, 1, 2.
• Jeannerod, M., Decety, J., and Michel, F. (1994). 'Impairment of grasping following a bilateral posterior parietal lesion'. Neurophysiologia, 32.
• Llinás, R., and Ribary, U. (2001). 'Co-evolution of human consciousness and language'. Annals of the New York Academy of Sciences, 929.
• Weiskrantz, L. (1974). 'The interaction between occipital and temporal cortex in vision: an overview'. In Schmitt, F. O., and Worden, F. G. (eds.), The Neurosciences Third Study Program.

Susan Blackmore

Whenever we ask 'Am I conscious now?' the answer seems to be 'Yes'. We always seem to be consciously feeling, hearing, and seeing something. But how can the existence of millions of interconnected brain cells give rise to this personal, private, ineffable experience? Either we must answer this question, or show why it is the wrong question.

Ever since William James (1890) coined the phrase the 'stream of consciousness', it has seemed indisputable that this rich, flowing succession of thoughts and perceptions is what needs explaining. Research on the 'contents of consciousness', the 'neural correlates of consciousness', and popular global workspace models all depends on distinguishing between what is in and what is out of the conscious stream. But what if it simply is not like that? What if there is no stream and no experiencer?

In experiments on 'change blindness' people look at a picture of a complex scene and, just as they blink or move their eyes, some key feature of the picture is changed. Most of the time they simply do not notice. The effect is very robust and has been shown using cuts in film and video, by making the change just as a 'mud splash' hits the picture, and even in real-life situations. The changes can be very large or right in the centre of the display and still not be noticed.

These surprising results suggest that we do not hold in our heads a rich visual image of the world, for if we did we would surely notice the changes. Rather, during each fixation we see only a small area, and when our eyes move that information is lost, leaving at most only a sketchy description. We think there is rich detail in our stream of consciousness because if ever we forget something we can look again and there it is. By using the outside world as a memory, we get the illusion of seeing much more than we really do. This alone shows we are wrong about our stream of consciousness. The stream of sounds is peculiar in a different way. The classic example is when the clock chimes several times before you notice. At that point you can distinctly count the number of chimes — chimes you did not consciously hear. With practice it is possible to pull out several such sound threads and, as it were, rehear the past few moments in different ways. Which then was really in the stream of consciousness?

One way of understanding these oddities is to replace the notion of a continuous stream with the idea that much of the time there is no distinction between 'in' and 'out' of consciousness. Then every so often we wonder 'Am I conscious now?' and an answer is concocted, backwards, from memory. A stream of consciousness and a self who observes it, both appear together — and both are illusions.

This may not be how it seems, but then how it seems can change dramatically with a little practice and attention. Perhaps we might even see through the illusion.

(Published 2004)

Bibliography
• Blackmore, S. (2003). Consciousness: An Introduction.
• Dennett, D. C. (1991). Consciousness Explained.
• James, W. (1890). The Principles of Psychology (2 vols.).
• Metzinger., T. (ed.) (2000). Neural Correlates of Consciousness.
• Nok, A. (ed.) (2002). Is the Visual World a Grand Illusion?

Ned Block

There are two broad classes of empirical theories of consciousness, which I will call the biological and the functional. The biological approach is based on empirical correlations between experience and the brain. For example, there is a great deal of evidence that the neural correlate of visual experience is activity in a set of occipitotemporal pathways, with special emphasis on the inferotemporal cortex.

The functionalist approach is a successor of behaviourism, the view that mentality can be seen as tendencies to emit certain behavioural outputs given certain sensory inputs. The trouble with behaviourism is that it did not allow that mental states were causes and effects, but functionalists do allow this. They characterize consciousness in terms of its causal role: the causal influence on it from inputs and other mental states, and its causal efficacy with respect to other mental states and behaviour. The central idea of functionalism is a proposal about the concept of consciousness, but scientific functionalists have filled the view in with empirical details — the idea is that a representation is conscious if it is broadcast in a global neuronal workspace. (See the article by S. Dehaene in Dehaene 2001.)

The functional approach says consciousness is a role, whereas the biological approach says consciousness is a realizer of that role. For example, one could take solubility to be a role — dissolving in certain circumstances — or, as with the biological view of consciousness, the physicochemical configuration that has that role.

The key empirical difference comes down to the question of whether consciousness might sometimes exist without having its normal role or whether something else might in some circumstances play that role. There is some evidence for the first possibility. There are unusual circumstances in which the occipitotemporal stream is activated at the level that is correlated with experience but in which the subject says he sees nothing. For example, there is a kind of brain damage in which, if objects are presented on both sides, the subject claims not to see one side, but the part of the occipitotemporal stream stimulated by the 'invisible' object is just as active as when it is seen. (See the articles by Kanwisher and by Driver and Vuillemer, in Dehaene 2001.) It seems possible that these patients have a phenomenal representation that they cannot properly access. If so, a phenomenal state needn't always have its characteristic behaviour, and consciousness in one sense of the term — phenomenality — would not be captured by the functionalist theory. (See also .)

Liss (1968) presented subjects with four letters in two circumstances, long, e.g. 40 milliseconds followed by a 'mask' known to make stimuli hard to identify, or short, e.g. 9 milliseconds, without a mask. Subjects could identify three of the four letters on average in the short case but said they were weak and fuzzy. In the long case, they could identify only one letter, but said they could see them all and that the letters were sharper, brighter, and higher in contrast. This experiment suggests a double dissociation: the short stimuli were phenomenally poor but perceptually and conceptually OK, whereas the long stimuli were phenomenally sharp but perceptually or conceptually poor, as reflected in the low reportability.

The picture that emerges is that phenomenality and accessibility may vary somewhat independently and that there is one concept of consciousness keyed to the former and another keyed to the latter. Phenomenality may be best thought of in biological terms, whereas accessibility is best thought of in terms of global neuronal broadcasting.

(Published 2004)

Bibliography
• Dehaene, S. (ed.) (2001). The Cognitive Neuroscience of Consciousness.
• Liss, P. (1968). 'Does backward masking by visual noise stop stimulus processing?' Perception and Psychophysics, 4.

David Chalmers

The conscious life of a subject comprises all sorts of subjective experiences: visual experiences, other sensory experiences, bodily sensations, mental imagery, and a stream of occurrent thought. There is something it is like to have these experiences, from the subject's point of view. The hard problem of consciousness is that of explaining how it is that physical processes in a brain are associated with experiences of this sort.

The problems of explaining how the brain supports complex behaviour, memory, learning, and language are 'easy' problems in comparison. These problems all concern the objective functioning of the brain, and can be approached by specifying appropriate neural or computational mechanisms. The hard problem, by contrast, concerns the relationship between objective functioning and subjective experience. Even once one has explained all the complex functions above, there may still arise a further question: why is there something it feels like to be a system of this sort? This is the key mystery of consciousness.

The fundamental issue concerns how to integrate two sorts of data about the mind. We have 'third-person data' about the brain and we have 'first-person data' about subjective experiences. Both are equally real, and both need to be explained. The task of a science of consciousness is to integrate them into a single framework.

In my view, we cannot 'reduce' first-person data to third-person data. If one's catalogue of what needs to be explained mentions only third-person data, one is simply overlooking some of the most important data that a science needs to explain. More controversially, I think that we cannot wholly 'explain' first-person data in terms of the third-person data. Third-person data is all data about objective structure and functioning. From this sort of data, one can deduce more third-person data about higher-level structure and functioning. But first-person data is not data about structure and functioning, so the gap is as wide as ever.

Instead, I think a science of consciousness needs to admit both first-person data and third-person data as real and mutually irreducible. The task of a science of consciousness is to investigate the systematic connection between these. First-person data can be gathered directly, through phenomenological methods, or indirectly, by inference from others' verbal reports. Third-person data can be gathered by the usual methods of psychology and neuroscience. One can then find systematic 'correlations' between the two. For example, conscious experiences seem to correlate directly with certain sorts of brain processes. We can eventually hope to find a highly detailed set of correlations between properties of the brain and properties of consciousness. Once this is done, we can attempt to infer a set of underlying 'fundamental principles' connecting physical processes and consciousness. If all goes well, these principles will be simple, basic, and universal.

As I see things, this will not 'reduce' consciousness to a brain process. The fundamental principles here will be analogous in some respects to fundamental laws of nature; on this view, consciousness can itself be seen as fundamental. But importantly, all this is quite compatible with the existence of a science of consciousness. I think that much recent work in the area can be seen as contributing toward a science of the sort I have outlined. There is a long way to go, and we do not yet know if all the obstacles can be overcome. But I think it is reasonable to hope that one day we will have a theory of the fundamental principles that connect physical processes to conscious experience.

Paul M. Churchland

This ill-defined topic, which has yet to find a governing research paradigm, is perhaps best defined by a series of unanswered questions. What distinguishes our waking state from such diverse states as deep sleep, trauma-induced coma, and the unconscious state induced by anaesthetics? Also, what distinguishes the brain's conscious representations and activities from the vast majority of its representational and computational activities that never ascend to that special status? Further, what structural, representational, or dynamical features of the brain are responsible for the emergence of conscious activity? And finally, what special functions does it perform that made conscious brains worthy of natural selection in the first place?

Aspirant theories are plentiful, as are thought-provoking empirical data, but no success has joined them decisively. Herewith, a critical summary of some popular suggestions.Special location accounts. Because consciousness is partly or wholly abolished when certain circumscribed brain areas are damaged, it is tempting to identify neuronal activity in those areas as the basis or embodiment of consciousness. For example, unilateral lesions to the thalamic intralaminar nucleus typically produce in the agent a profound hemineglect on the contralateral side, and bilateral lesions yield permanent coma (Bogen 1995). But for any suggested location, we want an explanation of what is special about the activities therein. This lacuna leads theorists to a variety of functional accounts.Self-representation accounts. On these, consciousness is said to occur when the brain perceives, or otherwise represents, some of its own cognitive states and activities. Consciousness is thus a form of metacognition. The favoured subjects of such occasional meta-representations are thereby elevated into consciousness (Armstrong 1981, Lycan 1987, Damasio 1999). A standard objection is that this wrongly conflates one special case of consciousness — awareness-of-self — with the more general form of consciousness displayed when any awake, alert creature is selectively aware of some feature of its external environment. That phenomenon, presumably, need require no self-representation at all. Also, the brain is massively engaged in 'monitoring' its own states at all times, whereas only a very few of those states are ever present to consciousness.Self-control accounts. On these, a brain is conscious to the extent that it is modulating, manipulating, and steering its own cognitive activities. Consciousness is thus the mark of an agent that is partly autonomous in generating not just its own behaviour, but its own cognition as well (Churchland 1995, Damasio 1999, Taylor 2001). Objections parallel those just given for meta-perceptual accounts. An awake, alert agent can be conscious solely by virtue of steering its own gross motor behaviour. And a live brain engages in widespread self-modulation as a matter of course, whereas only a few of the activities thus modulated are ever present to consciousness. A deliberate hybrid of views 2 and 3 might alleviate the second of these two problems (states at the focus of both self-perception and self-modulation might be comparatively rare). But the first problem would remain.Competition for executive control accounts. These readdress the brain's control of the physical body. Consciousness is here portrayed as the solution to a serious problem confronting any system as complex as the brain, an organ with diverse subsystems devoted to monitoring and controlling a wide range of internal and external phenomena. These subsystems, it is said, are all in competition with one another for here-and-now control of how the body's motor and sensory systems are to be deployed. The current contents of anyone's consciousness are always the current representations of whichever brain subsystem has managed to elbow aside or eclipse the clamouring competition. Those representations are distinguished by their having at least temporary executive control — over our speech mechanisms and over the body as a whole — and also, perhaps, by their being made candidates for storage in long-term memory (Baars 1988, Dennett 1991). In the awake state, this competition is never-ending, and so the contents of consciousness are typically ephemeral.

One wants, of course, an account of the mechanism of such selective dominance or focal attention. Here the suggestions diverge. The global workspace account posits a distinct brain area to which the unconscious subsystems continually submit information, which information enters consciousness only when it is taken up as somehow relevant to the computational activities already under way in that focal workspace. Another version eschews any special area, and posits a process of shifting coalitions of spatially distributed neural activity, coalitions of neurons temporarily united by their mutual interaction, perhaps (Baars 1988, Leopold and Logothetis 1999), or by a temporary synchrony in their physiological activities, a synchrony that yields them a temporary collective dominance over non-synchronous neurons (Crick and Koch 1990, Singer 2000).Special architecture and dynamics accounts. Here we return to the brain's microarchitecture and dynamic profile in search of functional insights. Normal brains display an information-processing ladder that leads ever forward from sensory neuronal populations through many intermediate populations and ultimately to populations of motor neurons. But there are also many axonal back-projections from populations higher and later on the ladder to populations lower and earlier. These 'descending' or 'recurrent' pathways introduce an intriguing variety of dynamic possibilities — such as self-modulation, selective attention, and autonomous activity — of interest to all of the functional accounts just scouted (Edelman 1993, Churchland 1995).

In particular, such a recurrent network can be configured so as to generate, autonomously, an unfolding trajectory in its neuronal activation space, a trajectory that partially represents an unfolding external reality. That trajectory can be continuously steered and edited by sensory input during the awake state; it can be left to wander freely during a disconnected 'dreaming' state, and it can be shut down entirely by the suppression of recurrent activity during 'deep sleep' (Llinás 2001).

These considerations hint that consciousness can come in a wide variety of degrees and flavours, depending on the character, the location, and the extent of such recurrent modulatory activity. Consciousness, some say, is like a light bulb — either it's on or it's off (Searle 1992). But perhaps not. A better analogy might be with light itself — which comes in endlessly different wavelength profiles and radiant intensities. Understanding light is a matter of grasping the relevant dimensions of variation. And just as genuine instances of light can vary widely along such dimensions, perhaps genuine consciousness may vary substantially from one species to another; or from one individual to another; or indeed, within a single individual over time.Extravagant accounts. These deserve mention for reasons of history and completeness, but they look increasingly barren as sources of fecund research. Dualism posits an immaterial substance, distinct from the brain, in which consciousness inheres, forever beyond the explanatory reach of the physical sciences (Popper and Eccles 1978). Epiphenomenalism posits, not a substance, but a range of non-physical properties of the brain, similarly beyond any physical explanation (Jackson 1982, Chalmers 1996). And a recent suggestion posits quantum-gravitational coherence within the microtubules of the brain's axonal fibres as the hallmark or essence of consciousness, on grounds that blocking such coherence may explain how anaesthetics work, while the achievement of such quantum-level coherences may explain the existence of sound but non-algorithmic mathematical knowledge (Penrose 1994). Such options may be discussed in undergraduate classes, or in the media, but they play a negligible role in guiding empirical research.

(Published 2004)

Bibliography
• Armstrong, D. (1981). The Nature of Mind.
• Baars, B. J. (1988). A Cognitive Theory of Consciousness.
• Bogen, J. E. (1995). 'On the neurophysiology of consciousness: an overview'. Consciousness and Cognition, 4.
• Chalmers, D. (1996). The Conscious Mind.
• Churchland, P. M. (1995). The Engine of Reason, The Seat of the Soul: A Philosophical Journey into the Brain.
• Crick, F., and Koch, C. (1990). 'Towards a neurobiological theory of consciousness'. Seminars in the Neurosciences, 2.
• Damasio, A. (1999). The Feeling of What Happens.
• Dennett, D. C. (1991). Consciousness Explained.
• Edelman, G. (1993). 'Neural Darwinism: selection and re-entrant signalling in higher brain function'. Neuron, 10.
• Jackson, F. (1982). 'Epiphenomenal qualia'. Philosophical Quarterly, 32.
• Leopold, D. A., and Logothetis, N. K. (1999). 'Multistable phenomena: changing views in perception'. Trends in Cognitive Science, 3.
• Llinás, R. (2001). I of the Vortex: From Neurons to Self.
• Lycan, W. (1987). Consciousness.
• Penrose, Roger (1994). Shadows of the Mind.
• Popper, K., and Eccles, J. (1978). The Self and its Brain.
• Searle, John (1992). The Rediscovery of the Mind.
• Singer, W. (2000). 'Phenomenal awareness and consciousness from a neurobiological perspective'. In Metzinger, T. (ed.), Neural Correlates of Consciousness.
• Taylor, J. G. (2001). 'The central representation: the where, what and how of consciousness'. In Colona, S. (ed.), The Emergence of Mind.

Dan Dennett

Consciousness often seems to be utterly mysterious. I suspect that the principal cause of this bafflement is a sort of accounting error that is engendered by a familiar series of challenges and responses. A simplified version of one such path to mysteryland runs as follows:












Thus we arrive in mysteryland. If you define qualia as intrinsic properties of experiences considered in isolation from all their causes and effects, logically independent of all dispositional properties, then they are logically guaranteed to elude all broad functional analysis — but it is an empty victory, since there is no reason to believe such properties exist. To see this, compare the qualia of experience to the value of money. Some naive Americans cannot get it out of their heads that dollars, unlike francs and marks and yen, have intrinsic value ('How much is that in real money?'). They are quite content to 'reduce' the value of other currencies in dispositional terms to their exchange rate with dollars (or goods and services), but they have a hunch that dollars are different. Every dollar, they declare, has something logically independent of its functionalistic exchange powers, which we might call its vim. So defined, the vim of each dollar is guaranteed to elude the theories of economists forever, but we have no reason to believe in it — aside from the heartfelt hunches of those naive Americans, which can be explained without being honoured.

Some participants in the consciousness debates simply demand, flat out, that their intuitions about phenomenal properties are a non-negotiable starting point for any science of consciousness. Such a conviction must be considered an interesting symptom, deserving a diagnosis, a datum that any science of consciousness must account for, in the same spirit that economists and psychologists might set out to explain why it is that so many people succumb to the potent illusion that money has intrinsic value.

There are many properties of conscious states that can and should be subjected to further scientific investigation right now, and once we get accounts of them in place, we may well find that they satisfy us as an explanation of what consciousness is. After all, this is what has happened in the case of the erstwhile mystery of what life is. Vitalism — the insistence that there is some big, mysterious, extra ingredient in all living things — turns out to have been not a deep insight but a failure of imagination. Inspired by that happy success story, we can proceed with our scientific exploration of consciousness If the day arrives when all these acknowledged debts are paid and we plainly see that something big is missing (it should stick out like a sore thumb at some point, if it is really important), those with the unshakeable hunch will get to say they told us so. In the meantime, they can worry about how to fend off the diagnosis that they, like the vitalists before them, have been misled by an illusion.

Ian Glynn

So far as we can tell, consciousness is always associated with nervous activity in a complex brain, and it is clear that interference with such activity — by changes in sensory input, or injury, or disease, or drugs, or direct electrical stimulation — can alter conscious states. It therefore seems likely that individual conscious states can exist only in the presence of particular patterns of nervous activity, and that the existence of these patterns is always associated with the corresponding conscious states. It is such patterns that are referred to as the neural correlates of consciousness. Why certain patterns of nervous activity should be always associated with certain thoughts or feelings is, of course, among the most difficult of all problems, but determining what these patterns are would seem to be a necessary first step — though only a first step — towards solving it.

It is a first step that is surprisingly difficult to take. Stimulating various sense organs is the usual way to produce a variety of sensations, and we know a good deal about many of the neural events that are links in the causative chains involved. A direct approach would therefore be to follow along the chain of events initiated by some sensation- or perception-causing stimulus, in the hope that at some stage it would lead to a pattern of neural events that not only correlated well with the current 'contents of consciousness' but which could be shown to be both necessary and sufficient for causing those particular thoughts or feelings. That is a very tall order indeed, not just because of the difficulty of elucidating the neural machinery likely to be involved, but also because of the need to monitor the contents of consciousness during the investigation.

The most successful attempts, so far, have involved first exposing a monkey to a stimulus that is ambiguous and can give rise to two different conscious perceptions, then training the monkey to indicate which perception it currently has (and when there is a change), and finally looking for neurons in the monkey's brain whose behaviour changes when the perception changes. The point of this procedure is that, because the stimulus remains constant, all the early processing should remain constant, and neurons whose behaviour changes when the perception changes are likely (though not certain) to be part of the machinery specifically involved in conscious perception. Ingenious experiments along these lines have been done by Nikos Logothetis and his colleagues, and by others. Another approach has been to look for neural activity associated with illusory perceptions.

These approaches are, of course, limited to situations in which the contents of consciousness are determined by something in the current environment acting through sensory pathways. Conscious memories must involve the neural machinery in which the memories are stored, and it seems likely that the conscious remembering of a past perception or event involves the partial re-creation, in appropriate areas of the cerebral cortex, of the patterns of activity caused by the perception or event at the time it was experienced. If that is right, the conscious aspect of a memory could depend on the same (unknown) machinery that allows us to be conscious of current perceptions and events.

If individual mental states and processes are inseparable from particular patterns of neural activity, they can have effects in the physical world, and the evolution of consciousness through natural selection is a plausible and attractive hypothesis. There is, though, a difficulty — first pointed out by William James in 1879. A strong correlation exists between the pleasantness or unpleasantness of sensations and the survival value (or threat to survival) of the situations that engender them. We like eating, drinking, and making love; we dislike hunger, injury, exhaustion. If we believe in old-fashioned, common-sense, interactive dualism, this correlation is to be expected; our mental states influence our behaviour, so, for our ancestors to have survived, their mental preferences must have tended to favour their survival. But once this belief in interactive dualism is relinquished (as it now generally is), and we assume that it is only through their neural correlates that mental events can influence behaviour, the subjective character of mental processes seems irrelevant. Why, then, is there this association between pleasure and situations promoting survival, and between discomfort and situations threatening survival? Whether study of the neural correlates of consciousness will help to solve this problem remains to be seen.

(Published 2004)

Bibliography
• Crick, F., and Koch, C. (2000). 'Some thoughts on consciousness and neuroscience'. In Gazzaniga, M. S. (ed.), The New Cognitive Neurosciences.
• Glynn, I. (1999). An Anatomy of Thought: The Origin and Machinery of the Mind.

Richard L. Gregory

1. Flagging the present
2. Exceptional cases

1. Flagging the present

One can imagine a bunch of interacting robots getting on fine without any awareness, or qualia, but surely they would not spend hours looking at pictures or listening to Beethoven. This is just how, only a few decades ago, behaviourist psychologists described us — as lacking qualia of red or pain, or the sound of violins. Why audiences without music qualia would sit through a symphony was hardly questioned. Psychology has now abandoned the behaviourism of J. B. Watson and B. F. Skinner, who tried to make psychology seem more scientific and less whimsical by denying consciousness, though at the cost of throwing out the baby with the bathwater. The situation is indeed reversed, as physicists, especially Roger Penrose, are now asking how the physical world can have consciousness.

Why should consciousness have evolved if it is useless? Yet, if qualia affect the nervous system, how can chemistry and physiology give adequate explanations of how the brain works, to give learning, perception, and behaviour?

We might hazard a guess at what qualia do. As perception depends on rich knowledge from the past, stored in the brain, there must surely be a problem identifying the present moment from past memories. And also from anticipations running into the future. As human perceptions are very largely stored knowledge, the present moment needs to be identified, for our behaviour to be appropriate to what is happening now. It is vitally important to recognize the present as special — as the only time that actions can occur. Crossing the road, it is essential to know that the green light is now, not in some remembered or anticipated time.

There is no such problem for primitive reflex actions. The present is signalled purely and simply by the onset of stimuli; but with rich memory and imagination, there must be a problem identifying neural activity of present stimuli, from memory and anticipation of other times. Our present, though signalled by stimuli, seems to be marked or 'flagged' by qualia.

Try this simple experiment. Look at the scene around you. Then close your eyes, and imagine it. What happens? Surely the vividness of the scene is lost. Memory and imagination are dim by comparison with the present. To reverse the experiment: imagine the scene, or a particular object known to be out there, then open the eyes and look at it. The qualia of the present visual world are suddenly startlingly vivid. So, perhaps an important role for qualia is to flag the present, so we are not confused with remembered past or anticipated future.

2. Exceptional cases

This is not infallible. At least one person with exceptionally vivid memories has been described who confused memories with present reality. This is the remarkable case of Mr S, described by the Russian neuropsychologist Alexander Luria. Mr S was a professional memory man, with incredibly vast memory and extremely vivid imagination. But he confused his vivid memories with real-time reality, to the point of danger. He would confuse imagined with real traffic lights. And, as he said, 'I'd look at a clock and for a long while continue to see the hands fixed just as they were, and not realize time had passed ... That's why I'm often late.'

Another exception is dreams. In dreams vivid qualia unrelated to present sensory signals may be experienced. But in sleep, in a safe place, the present moment has no special significance, as the muscles are inhibited and behaviour is essentially absent.

When sensory inputs are cut off for a long period, perception may become abnormal as in isolation experiments. In schizophrenia, and hallucinogenic drug-induced states, vivid qualia are also experienced with no sensory input. We may assume the normal qualia-flagging-the-present system is malfunctioning with sleep, and in schizophrenia and hallucinogens. Then the hypothesis is 'saved', and perhaps we have learned more about these states.

It is reported that in drug-induced states, time may seem to slow or stop. In Doors of Perception (1954), Aldous Huxley describes changes of consciousness experienced with mescaline. He ceased to be interested in action, becoming a passive observer — 'the will suffers a profound change for the worse' — though his ability to think is little if at all reduced. So he becomes almost a 'not-self'. Most suggestive: 'Visual impressions are greatly intensified', while 'interest in space is diminished and interest in time falls almost to zero'. Huxley emphasizes that colours are immeasurably enhanced in vividness, ordinary objects appearing self-luminous, with the inner fire of jewels, while time essentially stops — becoming 'an indefinite duration alternatively a perpetual present'. With mescaline and other hallucinogenic drugs sensations become enhanced, as super qualia, and the present is emphasized with correspondingly little flow of time.

Although memories usually lack visual or other qualia, sensations are surprisingly vivid in remembered emotions, as when an embarrassing situation is recalled years later. With the Danish physician Carl Lange, William James suggested that emotions have a basis in autonomic changes of the body. The James–Lange theory of the emotions is that the body responds, for example to danger, by unconsciously preparing for action, and these autonomic physiological changes are then sensed as emotions of fear or rage or whatever.

For the emotion of shame, there is autonomic change with visible blushing. Darwin suggested that blushing is a social signal warning others that this person is not to be trusted. We may blush at the memory of a shame-making deed, experiencing qualia of shame years after the event — presumably when afferent inputs from autonomic bodily changes are evoked by memories. These autonomic changes are in the present, so this is not really an exceptional case.

This idea of flagging the present by qualia has implications for consciousness in other animals. As perception evolved, to become more intelligent, it drew away from direct control by stimuli. But as intelligence cannot be tied to the sensed present they can be dangerous. Imagination and intelligence push the mind away from present reality, but nudges of qualia seem to bring us to our senses, to handle the present situation in real time.

Bibliography
• Luria, A. (1969). The Mind of a Mnemonist: A Little Book about a Vast Memory.
• Huxley, A. (1968). The Complete Works of Aldous Huxley.
• James, W. (1890). Principles of Psychology.
• Darwin, C. R. (1872). Expression of the Emotions in Man and Animals.

Nicholas Humphrey

Fashions change. The problem of consciousness, once banned from serious consideration by psychologists, is again high on the agenda. Yet typically researchers are looking under the lamp that currently shines brightest rather than in the area where the phenomenon went missing. They are identifying consciousness with high-level thought processes and seeking to explain it in 'thinking machine' terms, but they are largely ignoring bodily feeling.

Yet if we listen to the kinds of questions ordinary people ask — 'Are babies conscious?', 'Will I be conscious during the operation?', and so on — it is clear that, again and again, the central issue is not thinking but feeling. People's concern is not with the stream of thoughts that may or may not be running through their heads but with the sense they have of being alive at all — which is to say, alive and living in the presence of sensation. The problem, then, is to explain just what these sensations — conscious sensations — are. We want a theory of why it feels to us as it does to taste salt on our tongues, to look at the blue sky with our eyes, to burn our fingers on the stove. But — and here is what is going to make this problem hard — the theory must not beg the question by assuming any prior acquaintance with what is being explained: namely, sensory consciousness as such.

Let's stipulate, then, that the theory has to be comprehensible to a scientist from Mars — an individual in many ways not unlike ourselves, highly intelligent, perceptive, and even capable of self-reflection, but who none the less has never evolved into the kind of being who has sensations. Suppose we could explain to this Martian what happens in the brain of a human being who is engaged, say, in smelling a rose. And suppose he could thereby arrive at the entirely novel (to him) conclusion that it must be like something to be this human being, and indeed like this: 'I am feeling this thick, sweet, olfactory sensation in my nostrils.' It's a tall order, but, still, it is what the theory ought to do.

Is a theory, which could bring this off, a possibility even in principle? Since the theory must employ only such concepts as the Martian can make sense of at the outset, we need to consider what kind of pre-theoretical notions he brings with him. Given that as yet he knows nothing about sensations, will he have other essential concepts on which to build?

We want him to understand that the human being is the subject of sensations. Can we assume he will at least have, to start with, the idea of what it is to be a 'subject'? I'd say we can. For presumably the Martian is already himself a subject in the following crucial sense: an autonomous agent who acts in the world. Provided he can take himself as a model, he ought already to have the basic concept of an 'I'. Then, can we assume he also understands the idea of being the 'subject of' something? Again, we can. For, as an 'I' who does things with his body, he himself already has this genitive relationship to his own actions: he is the author of everything he does. So, will he even have the idea of being the subject of something with some of the peculiar properties of sensations: especially, that

(i) they belong to the subject,
(ii) they implicate part of his body,
(iii) they are present tense,
(iv) they have a qualitative modality,
(v) their properties are phenomenally immediate? In fact he will: for analysis shows that bodily actions already have precisely these characteristics (i)–(v).

Now, this may not seem much as a basis for understanding sensory consciousness. But I believe that, with the right theory, it will be enough. Suppose we suggest the following theory to the Martian (it is my theory, but others like it might also do the trick).

When a person smells a rose, he responds to what's happening at his nostrils with a 'virtual action pattern': one of a set of action patterns that originated far back in evolutionary history as evaluative responses to various kinds of stimulation at the body surface — wriggles of acceptance or rejection. In modern human beings these responses are still directed to the site of stimulation, and still retain vestiges of their original function and hedonic tone; but today, instead of carrying through into overt behaviour, they have become closed off within internal circuits in the brain; in fact the efferent signals now project only as far as the sensory cortex, where they interact with the incoming signals from the sense organs to create, momentarily, a self-entangling, recursive, loop. The theory is that the person's sensation, the way he represents what's happening to him and how he feels about it, comes through monitoring his own signals for the action pattern — as extended, by this recursion, into the 'thick moment' of the conscious present.

Then, how will the Martian understand this? Presumably nothing in his own direct experience corresponds to what we have just described to him. But, still, he should be able to work it out. He will be able to grasp the key fact that sensation consists in monitoring commands for action in response to stimulation. He will be able to appreciate the peculiar features of the action pattern that has in fact evolved. And so he will be able to work out that, if a subject like himself were to get involved in doing what the human being is doing, the result would be that he would have just these beliefs about it, these attitudes, these things to say, these that he cannot say, and so on — in short he would experience it like this.

But if the Martian can work all this out from the theory, would this mean he actually acquires first-hand experience of sensations in the process? No: no more than someone who works out from physics and chemistry that H₂O makes water gets wet. A theory of consciousness is not a way of conferring consciousness; it is a way of understanding why consciousness-generating brain states have the effects on people's minds they do. The Martian himself may indeed have no sense organ with which to smell the rose at all: and yet, if the theory is right, he will still be able to discover all that we ourselves can discover by direct acquaintance. (One day, of course, when we get to study Martians, the boot may be on the other foot.)

(Published 2004)

Bibliography
• Humphrey, N. (1992). A History of the Mind.

David Papineau

To many it seems obvious that the conscious mind must be distinct from the physical brain. How could mere neural activity possibly constitute the vibrant subjective world of colour experience, pain, and emotion?

However, this dualist intuition should be resisted. The cost of dualism is epiphenomenalism — that is, the doctrine that conscious experiences are mere side effects of brain activity, and do not themselves affect our physical behaviour. This follows because modern physiological science has shown convincingly that all limb movements, muscle contractions, and so on are caused solely by neural and other purely physical antecedents. This leaves no room for a distinct realm of conscious experience to make a difference to what we do.

If we are to avoid this absurd epiphenomenalist conclusion, we therefore have no option but to deny dualism, and identify conscious experiences with the neural causes of behaviour.

But, again, how could mere neural activity constitute conscious experience? A first step towards an answer is to admit that, even if the conscious mind is identical to the physical brain, we humans have two quite different ways of thinking about this single realm: we can conceive of it as physical, or we can conceive of it in terms of how it feels. (Suppose the dentist's drill were to slip on your next visit. You can think of the result in terms of nociceptive-specific neuronal activity. Or you can think of it in terms of how it would feel to you.)

Following David Chalmers (1996), I shall say that the latter mode of thought deploys a 'phenomenal concept', and I shall take the exercise of such phenomenal concepts to involve powers of imagination and introspection. However, as a physicalist, and unlike Chalmers, I take phenomenal concepts to refer to just the selfsame neural items as we refer to using physical concepts of the mind–brain. (When you think of what the tooth pain would feel like you refer to just the same thing in reality as when you think of nociceptive-specific neuronal activity — just as when you think of Judy Garland you refer to just the same person in reality as when you think of Frances Gumm.)

Not all physicalists recognize distinct phenomenal concepts. But physicalists are far better off with them than without them. For one thing, phenomenal concepts allow physicalists to explain why mere knowledge of brains as such will never tell you what some experience feels like: the point is that 'knowing what it's like' requires phenomenal concepts, and you cannot get these from brain science; rather, you typically need to have had the experience yourself, to develop the requisite powers of imagination and introspection.

In addition, the special structure of phenomenal concepts can help explain why mind–brain identity seems so persistently counter-intuitive (unlike the identity of Judy Garland and Frances Gumm). When we think about conscious items phenomenally, we typically imagine or introspect those same items. Not so when we think about them as physical. So it can strike us that the physical concepts 'leave out' the experiences themselves. And in a sense they do: they do not activate those experiences in the way phenomenal concepts do. But it is a fallacy — which elsewhere (2002) I dub 'the antipathetic fallacy' — to conclude that physical concepts do not refer to the experiences themselves. After all, most concepts do not activate the things they refer to.

As a physicalist, I hold that phenomenal concepts refer to physical items. But since phenomenal concepts are distinct from physical concepts, it need not be immediately clear which specific physical items they refer to. It is a task for science to identify the physical referents of phenomenal concepts. This is how a physicalist will think of Chalmers's 'hard problem'. The scientific problem of consciousness isn't just the (relatively) easy matter of understanding the brain in physical terms. We also want to know which brain processes are referred to by such phenomenal concepts as pain, or seeing something red, or indeed feeling like anything.

However, once we get this 'hard problem' into proper focus, there is reason to doubt that it will admit of very definite answers. We may be able to identify brain processes that are present in humans whenever they are phenomenally aware of themselves as in pain, or seeing something red, or feeling like anything. But nothing will tell us which specific features of these brain processes are referred to by these phenomenal concepts, nor correspondingly whether non-human creatures, who will share some of these features but not others, will fall under these concepts.

This doesn't mean that there is some mystery about consciousness that lies beyond science. The trouble is simply that all phenomenal concepts are vague. They offer crude, ancestral ways of thinking about conscious states, and because of this go fuzzy when stretched beyond their normal application to humans.

(Published 2004)

Bibliography
• Chalmers, D. (1996). The Conscious Mind.
• Papineau, D. (2000). Introducing Consciousness.
• — —  (2002). Thinking about Consciousness.

Roger Penrose

Most scientific discussions concerning the nature of consciousness attempt to find an explanation for this phenomenon in terms of the physical picture of the world that is known today. Particularly popular is computational functionalism (or strong AI), which asserts that it is entirely the computational action of the pattern of neuron firings and synaptic responses that is responsible for our awareness, our feelings of free will, and other aspects of consciousness. Some neurophysiologists argue that the computational model is inadequate and that the detailed neurochemistry of the brain must play an essential role in determining consciousness. Still others would claim that the physics of quantum theory is a key ingredient, and that free will is dependent on quantum indeterminism.

None of these standpoints demands that we move beyond our present physical world-view, and most of them do not even regard quantum phenomena as having any significant role to play. Yet, quantum theory is part of our current world-view and is, by now, extremely well established. No confirmed experiment that has been performed to date contradicts the expectations of quantum theory, and many such experiments clearly demonstrate the physical need for this theory. Yet it seems that most neurophysiologists are sceptical that quantum phenomena could have any particular role in brain action beyond determining such things as the rules of chemistry, the physical nature of action potentials, etc.

All this notwithstanding, I believe that there are strong reasons to expect: (a) irrespective of any considerations of the nature of consciousness, even existing quantum theory provides an inadequate world-view for physics and will have to be replaced by an ontologically more satisfactory and (ultimately) observationally distinct physical theory; and (b) the phenomenon of consciousness must be physically dependent upon the distinctive features of such a yet-to-be-discovered physical theory. What are the reasons for my expectations (a) and (b)? The reasons behind (a) come entirely from within physics itself, as do specific suggestions for moving beyond present-day quantum theory, and they do not call upon any belief in the inadequacy of present-day physics to accommodate the phenomenon of consciousness (cf. Penrose 1994). The reasons behind (b) are, on the other hand, largely indirect. They depend upon certain arguments against the computational model of consciousness, coupled with the fact that present-day physics provides us with an essentially computational picture of physical action (cf. Penrose 1994).

This is not the place to expound at length upon (a), but the basis of my argument has to do with the superposition principle of quantum mechanics, which demands that quantum objects can be put into a state of superposition of two separate locations at the same time. Such superpositions are observed to occur for individual particles such as photons or neutrons, or even complicated molecules such as carbon-60 fullerenes, but they lead to absurdities for genuinely macroscopic objects, such as Schrödinger's (hypothetical) cat, forced into a superposition of death and life. Although there is no consensus as to how to resolve this apparent contradiction — known, generally, as the measurement paradox — one school of thought maintains that no adequate resolution is possible without a change in the very structure of quantum mechanics. Within this school, there is a sizeable faction which contends that gravitational effects are responsible. According to the most clear-cut scheme along these lines (referred to as gravitational objective reduction or OR), a macroscopic quantum superposition of two distinct stationary states would decay into one or other of these constituent states in a time scale which can be computed knowing the two mass distributions involved (and which would be almost instantaneous for a cat). There are difficult but technically feasible experiments which could settle the correctness of this contention. These are presently in the development stage.

The main arguments behind (b) come from the nature of human understanding, particularly mathematical understanding. Understanding is a quality that requires consciousness, and there are reasons, coming from the famous theorem of mathematical logic, known as Gödel's incompleteness theorem, to believe that mathematical understanding cannot be reduced to any purely computational activity. This theorem can be paraphrased as follows: given any (sufficiently broad) computational system R of rules of proof which we believe to be sound (i.e. to be such that the rigorous following of the rules R yields only truths and no falsehoods), then one can construct a clear-cut mathematical statement G(R) whose truth can be seen to be a consequence of the soundness of R, yet which cannot be deduced by actually following the rules of R. Thus our belief in G(R) cannot be a consequence of our actual use of R, but follows from our acceptance of R as a valid proof procedure. From this (and some further detailed considerations) it is argued that our access to mathematical truth transcends any purely computational proof procedure. Accordingly, understanding in general is not simply a matter of computation.

Various suggested counter-arguments have been put forward to circumvent this conclusion; most particularly, human reasoning is subject to error, and there is the possibility that we need not be aware of any particular 'R' that underlies our thinking. Both these counter-arguments (and numerous others) have been addressed in detail in the literature (see Penrose 1994).

One puzzling feature of conscious perception is what is referred to as the binding problem. In the conscious perception of an image, the various ingredients (such as colour, shape, and motion, in a visual image) may each be processed in widely separated parts of the brain; yet the image is perceived in its entirety without there being significant direct neural connections between these separate processing regions. In models of perception that depend upon gravitational OR, such non-locality is to be expected, this being a feature of the quantum measurement process. There are characteristically 'quantum' features of this non-locality ('violations of Bell inequalities' cf. Bell 1964, Penrose 1994: 237–49, 287–304) and it may be that these will show up in careful experiments on human perception (A. Duggins, personal communication 1999).

For gravitational OR to have a chance of direct relevance in brain activity, it is necessary for there to be structures in the brain that can support large-scale quantum coherence — without degradation of the quantum state via environmental decoherence — and which can influence synaptic function significantly. This presents severe difficulties, and it is clear that ordinary nerve signalling would not achieve this. The most promising suggestion is that neuronal (A-lattice) microtubules are responsible, and a fairly detailed model, referred to as 'orchestrated objective reduction' (Orch-OR) has been worked out by S. Hameroff and collaborators (Hameroff and Penrose 1996, Hameroff et al. 2002).

(Published 2004)

Bibliography
• Bell, J. S. (1964). 'On the Einstein Podolsky Rosen paradox'. Physics, 1. Reprinted in Wheeler, J. A., and Zurek, W. H. (eds.), Quantum Theory and Measurement.
• Hameroff, S., and Penrose, R. (1996). 'Orchestrated reduction of quantum coherence in brain microtubules: a model for consciousness?' In Hameroff, S. R., Kaszniak, A. W., and Scott, A. C. (eds.), Toward a Science of Consciousness: The First Tucson Discussions and Debates.
• — —  Nip, A., Porter, M., and Tuszynski, J. (2002). 'Conduction pathways in microtubules, biological quantum computation, and consciousness'. BioSystems, 64.
• Penrose, R. (1994). Shadows of the Mind: An Approach to the Missing Science of Consciousness.

Brian Pippard

Nineteenth-century scientists, in their work as in their daily lives, took for granted the reality of the world around them and sought to account for it at every level by the Newtonian mechanics which, on the human scale, appeared both reasonable and flawless. The forces of gravitation and electromagnetism demanded a medium, the aether — intangible but still Newtonian — by which they could operate across apparently empty space. Failure to invent a plausible model, the advent of Einstein's relativity, and finally quantum mechanics demolished this ideal programme. Action-at-a-distance was restored to the status of an unexplained mathematical rule, as Newton had been forced to leave it, and a succession of new fundamental particles had to be accepted even if their behaviour defied visualization. No longer could we conceive of a definite path connecting one event with the next; indeterminacy was an inevitable consequence of Schrödinger's equation, which gave the right answer to a vast range of problems. Despite many ingenious attempts, which are still being made, no consistent substitute has been found for the early Copenhagen doctrine that limits the scientist's business to the precise description and correlation of observations shared by competent investigators. Ultimate reality, whatever it may be, is a matter for metaphysicians, not scientists.

Within this constraint enormous progress has been made, but the rules of the game, however foreign to everyday intuition, have to be applied with mathematical rigour, even if it means sacrificing ancient beliefs. Thus emergence of life from inert matter can now be accepted as a manifestation of chemical versatility, and replication of the DNA molecule demands no intervention of a vital force. There is indeed a long and barely mapped road to be travelled before we shall appreciate how DNA leads to an undeniably living organism, but no one expects to find a need for new basic laws.

With man, and perhaps before him, what we suppose to be unthinking forms of life evolved to possess the power of thought. Is this also to be seen as a consequence of scientific laws? To be sure, when someone speaks, what he says and the measurable events (chemical, electrical, mechanical) accompanying his statements are public material for use in science; but the relationship between what he says and what he thinks is not, for his thought is private and unshared. My response to Mozart or to the pain in my leg is my pleasure or my pain; no one else can truly say he feels exactly like that — only, at best, that he would use the same words to describe what he felt. In any case, who can fully express in words his own thoughts and feelings?

Let us suppose we were asked to investigate a black box and analyse its responses. Even if we decided that in every way they matched the responses of a thinking creature, we should still not be justified, as scientists, in concluding 'it thinks', in the sense 'it is conscious of itself'. We might find it convenient to introduce into our calculations symbols representing consciousness, and display them in our answer, but this would be no more meaningful than our forebears' talk of aether, or our own of wave functions and fields. So long as we limit ourselves to observations we cannot go beyond 'as if it thinks'.

The two words 'as if' signal an important change in science since the 19th century. Had the basic laws proved to be intuitively comprehensible, as was once hoped, we might dare to believe that eventually our understanding of the external world — a reality existing independently of observation — might be extended to the point of embracing conscious thought. But now that our only reality is what we ourselves experience, we have no more fundamental terms in which to describe the central experience of conscious thought; we must accept that our science is powerless to make us understand that very faculty without which there would be no science.

Steven Rose

A few years ago I was at a conference at which a bright young Harvard neurophysiologist referred to the study of consciousness as a 'CLM' — a career-limiting move. Today however I fear that the way most neuroscientists approach the matter is itself a CLM — a consciousness-limiting move. The term consciousness has multiple rich meanings. Social and political sciences deal with such concepts as class, race, and gender consciousness. Philosophers may ponder the etymological relationship between consciousness and conscience. Psychoanalysts will contrast consciousness and 'the unconscious', by which they definitely do not mean what an anaesthetist or neurologist might imply. All these rich, social, historical, and personal developmental meanings are lost in the discourse of most neuroscientists. For them, being conscious is merely the antithesis of being asleep or unconscious in the anaesthetist's sense. Thus consciousness reduces to mere 'awareness' and the discussion then focuses on how the multitude of sense data impinging on our brains at any moment becomes ordered and refined into that most relevant for our immediate needs. Francis Crick in his book The Astonishing Hypothesis puts this most clearly, following with a further reductionist move: on the basis that more is known about the neurobiology of the visual system than that of any other sensory process, he proposes to exploit the neural mechanisms of perception as a model system, tractable to experiment (and ends the book with an aside locating free will in the anterior cingulate!).

The problem with such ploys is that they empty consciousness out of most of what the computational neuroscientists would doubtless dismiss as its 'folk meanings'. Yet these folk meanings are precisely the important ones if we are concerned with the relevance of neuroscience to an understanding of the human condition. We are not helped either by those philosophers of mind who worry over qualia, and how the objective becomes subjective. I have no problem with a two-aspect theory, an ontological unity but epistemological diversity in which brain language and mind language are no more primary and secondary than are English and Italian in referring to the brown furry creature sitting on my desk as I write as 'cat' and 'gatto's. The suggestion that this is the 'hard problem' in Chalmers's sense is simply a category confusion. This does not make me a New Mysterian in the McGinn sense either. It is simply to insist that we be clearer about the nature of the phenomenon or process that we regard as ontologically unitary.

By which I mean that I would argue that (a) consciousness is not a thing but a process, and that (b) as a process it is essentially social, being constituted in the relationship between a person and his or her social and physical milieu. This relationship is itself of course shaped by evolution, development, and history. Consciousness then is not simply 'in the brain'. At the very least it is embedded within the brain/body system, being as we know profoundly affected by, for instance, hormonal and immunological status. But far more than that, consciousness is expressible only as a relationship and is thus not physically located within an individual, and certainly not in a specific brain region. The more modest task of neuroscience then becomes not to explain, or worse, explain away, consciousness, nor to translate brain processes into qualia, but rather to look at those aspects of a person's evolved and developed neurobiology which enable them to have conscious experiences in all the multiple rich meanings of the term.

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Quotes:

"But they for whom I am the supreme goal, who do all work renouncing self for me and meditate on me with single-hearted devotion, these I will swiftly rescue from death's vast sea, for their consciousness has entered into me." - Bhagavad Gita

"The real history of consciousness starts with one's first lie." - Joseph Brodsky

"It is our less conscious thoughts and our less conscious actions which mainly mould our lives and the lives of those who spring from us." - Samuel Butler

"The unconscious is the ocean of the unsayable, of what has been expelled from the land of language, removed as a result of ancient prohibitions." - Italo Calvino

"A sub-clerk in the post-office is the equal of a conqueror if consciousness is common to them." - Albert Camus

"Consciousness is much more than the thorn, it is the dagger in the flesh." - E. M. Cioran

See more famous quotes about Consciousness

The state of being conscious; responsiveness of the brain to impressions made by the senses. Altered states range from the normal, complete alertness to depression, confusion, delirium and finally loss of consciousness.

n

A state in which the individual is capable of rational response to questioning and has all protective reflexes intact, including the ability to maintain a patent airway.

For a list of words related to consciousness, see:

• Notions, Ideas, and Methods - consciousness: awareness, sentience
• Mystical States and Experiences - consciousness: awareness, esp. of spiritual life

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This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

Common misspelling(s) of consciousness

• conciousness

Dansk (Danish)
n. - bevidsthed, forståelse

idioms:

• consciousness raising    bevidstgørelse, vækning af problembevidsthed

Nederlands (Dutch)
bewustzijn, besef

Français (French)
n. - conscience, conscience collective, (Méd) connaissance

idioms:

• consciousness raising    sensibilisation

Deutsch (German)
n. - Bewußtsein

idioms:

• consciousness raising    bewußtseinssteigernd

Ελληνική (Greek)
n. - συνείδηση

idioms:

• consciousness raising    αφύπνιση της κοινωνικής συνείδησης

Italiano (Italian)
coscienza, conoscenza

idioms:

• consciousness raising    il prendere coscienza
• lose consciousness    perdere conoscenza
• regain consciousness    riprendere conoscenza

Português (Portuguese)
n. - consciência (f), conhecimento (m)

idioms:

• consciousness raising    tornar-se consciente da discriminação contra um grupo particular de pessoas
• lose consciousness    perder a consciência
• regain consciousness    recobrar a consciência

Русский (Russian)
сознание, сознательность

idioms:

• consciousness raising    дать лучше знать
• lose consciousness    потерять сознание
• regain consciousness    прийти в себя

Español (Spanish)
n. - conciencia, conocimiento

idioms:

• consciousness raising    concienciación, concientización

Svenska (Swedish)
n. - medvetande, medvetenhet

中文（简体）(Chinese (Simplified))
意识, 自觉, 知觉

idioms:

• consciousness raising    提高觉悟, 增强意识

中文（繁體）(Chinese (Traditional))
n. - 意識, 自覺, 知覺

idioms:

• consciousness raising    提高覺悟, 增強意識

한국어 (Korean)
n. - 자각, 의식

日本語 (Japanese)
n. - 意識, 気づくこと, 精神

idioms:

• consciousness raising    自己発見

العربيه (Arabic)
‏(الاسم) يقظه, تنبه, وعي‏

עברית (Hebrew)
n. - ‮תודעה, מודעות, הכרה‬

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