Michael A. ArbibSusan BlackmoreNed BlockDavid ChalmersPaul M. ChurchlandDan DennettIan GlynnRichard L. GregoryNicholas HumphreyDavid PapineauRoger PenroseBrian PippardSteven RoseMichael 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:
phil. What is consciousness?
sy. Well, some things — such as stones and can-openers — are utterly lacking in any point of view, any subjectivity at all, while other things — such as you and me — do have points of view: private, perspectival, interior ways of being apprised of some limited aspects of the wider world and our bodies' relations to it. We lead our lives, suffering and enjoying, deciding and choosing our actions, guided by this 'first-person' access that we have. To be conscious is to be an agent with a point of view.
phil. But surely there is more to it than that! A cherry tree has limited access to the ambient temperature at its surface, and can be (mis-)guided into blooming inopportunely by unseasonable warm weather; a robot with video camera 'eyes' and microphone 'ears' may discriminate and respond aptly to hundreds of different aspects of its wider world; my own immune system can sense, discriminate, and respond appropriately (for the most part) to millions of different eventualities. Each of these is an agent (of sorts) with a point of view (of sorts) but none of them is conscious.
sy. Yes, indeed; there is more. We conscious beings have capabilities these simpler agents lack. We don't just notice things and respond to them; we notice that we notice things. More exactly, among the many discriminative states that our bodies may enter (including the states of our immune systems, our autonomic nervous systems, our digestive systems, and so forth), a subset of them can be discriminated in turn by higher-order discriminations which then become sources of guidance for higher-level control activities. In us, this recursive capacity for self-monitoring exhibits no clear limits — beyond those of available time and energy. If somebody throws a brick at you, you see it coming and duck. But you also discriminate the fact that you visually discriminated the projectile, and can then discriminate the further fact that you can tell visual from tactile discriminations (usually), and then go on to reflect on the fact that you are also able to recall recent sensory discriminations in some detail, and that there is a difference between experiencing something and recalling the experience of something, and between thinking about the difference between recollection and experience and thinking about the difference between seeing and hearing, and so forth, till bedtime.
phil. But surely there is more to it than that! Although existing robots may have quite paltry provisions for such recursive self-monitoring, I can readily imagine this particular capacity being added to some robot of the future. However deftly it exhibited its capacity to generate and react appropriately to 'reflective' analyses of its underlying discriminative states, it wouldn't be conscious — not the way we are.
sy. Are you sure you can imagine this?
phil. Oh yes, absolutely sure. There would be, perhaps, some sort of executive point of view definable by analysis of the power such a robot would have to control itself based on these reactive capacities, but this robotic subjectivity would be a pale shadow of ours. When it uttered 'it seems to me ...' its utterances wouldn't really mean anything — or at least, they wouldn't mean what I mean when I tell you what it's like to be me, how things seem to me.
sy. I don't know how you can be so confident of that, but in any case, you're right that there is more to consciousness than that. Our discriminative states are not just discriminable; they have the power to provoke preferences in us. Given choices between them, we are not indifferent, but these preferences are themselves subtle, variable, and highly dependent on other conditions. There is a time for chocolate and a time for cheese, a time for blue and a time for yellow. In short (and oversimplifying hugely), many if not all of our discriminative states have what might be called a dimension of affective valence. We care which states we are in, and this caring is reflected in our dispositions to change state.
phil. But surely there is more to it than that! When I contemplate the luscious warmth of the sunlight falling on that old brick wall, it's not just that I prefer looking at the bricks to looking down at the dirty pavement beneath them. I can readily imagine outfitting our imaginary robot with built-in preferences for every possible sequence of its internal states, but it would still not have anything like my conscious appreciation of the visual poetry of those craggy, rosy bricks.
sy. Yes, I grant it; there is more. For one thing, you have meta-preferences; perhaps you wish you could stop those sexual associations from interfering with your more exalted appreciation of the warmth of that sunlight on the bricks, but at the same time (roughly) you are delighted by the persistence of those saucy intruders, distracting as they are, but ... what was it you were trying to think about? Your stream of consciousness is replete with an apparently unending supply of associations. As each fleeting occupant of the position of greatest influence gives way to its successors, any attempt to halt this helter-skelter parade and monitor the details of the associations only generates a further flood of evanescent states, and so on. Coalitions of themes and projects may succeed in dominating 'attention' for some useful and highly productive period of time, fending off would-be digressions for quite a while, and creating the sense of an abiding self or ego taking charge of the whole operation. And so on.
phil. But surely there is more to it than that! And now I begin to see what is missing from your deliberately evasive list of additions. All these dispositions and meta-dispositions to enter into states and meta-states and meta-meta-states of reflection about reflection could be engineered (I dimly imagine) into some robot. The trajectory of its internal state switching could, I suppose, look strikingly similar to the 'first-person' account I might give of my own stream of consciousness, but those states of the robot would have no actual feel, no phenomenal properties at all! You're still leaving out what the philosophers call the qualia.
sy. Actually, I'm still leaving out lots of properties. I've hardly begun acknowledging all the oversimplifications of my story so far, but now you seem to want to pre-empt any further additions from me by insisting that there are properties of consciousness that are altogether different from the properties I've described so far. I thought I was adding 'phenomenal' properties in response to your challenge, but now you tell me I haven't even begun.. Before I can tell if I'm leaving these properties out, I have to know what they are. Can you give me a clear example of a phenomenal property? For instance, if I used to like a particular shade of yellow, but thanks to some traumatic experience (I got struck by a car of that colour, let's suppose), that shade of yellow now makes me very uneasy (whether or not it reminds me explicitly of the accident), would this suffice to change the phenomenal properties of my experience of that shade of yellow?
phil. Not necessarily. The dispositional property of making you uneasy is not itself a phenomenal property. Phenomenal properties are, by definition, not dispositional but rather intrinsic and accessible only from the first-person point of view ... .
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 cases1. 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 H
2O 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.