Anyone despairing at drawing up a definitive reading list on scientific approaches to consciousness that will not be obsolete within a week now has two more reasons for identifying with King Canute. These latest offerings by Bernard Baars and Lawrence Weiskrantz have much in common in that they are both grounded in cognitive, neuropsychological approaches. Baars's highly plausible launch pad is to consider experimental situations, with and without consciousness, to work out a theory for accounting for the disparity. Soon however, empirical desiderata give way to a metaphorical model of the theatre, which ends up as centrepiece. A theatre of the mind/brain is, of course, not new. For the ancients, the idea of a "theatre" of memory was attractive for enhancing mnemonic skills, while more recently, the idea caught on for illustrating the fallacy that there was an inner brain within a brain, as reviled so vividly by Daniel Dennett in his scathing image of the Cartesian theatre. Since most readers will thus already have their fingers on the reject button at the very mention of a theatre in any way connected with consciousness, Baars's metaphor, perhaps unfairly, will be hard to swallow first off. But is it helpful after all?
Certainly the image of the theatre provides a clear framework. The stage is itself small and limited, just like a moment of conscious experience. But behind that experience is a vast backup of off-stage activities, past and present, that has set the "context" that will give the momentary experience a particular quality. A central "idea" is never abstract, but rather an idiosyncratic inner kaleidoscope of literal images spawned by personal experience. The attention needed at that moment can be likened to a metaphorical spotlight already celebrated by Francis Crick in his approach to consciousness. Baars sees "attention" here, however, not so much as consciousness itself, but rather as the means for searching out what consciousness to have.
And once under way, this consciousness, the momentary performance, will inspire the "audience", the unconscious brain processes, to be pressed into service. True, a conscious thought, in order to leave room, sets in train a cascade of complex "unconscious" to-ing and fro-ing at a host of neuromuscular junctions. But the metaphor is particularly counter-intuitive: how can an audience be unconscious? It is similarly worrisome, and inevitable, that the theatre metaphor then leads Baars to reflect on who is directing the show, namely the self and its nature. A problem here however, is that the author does not draw clear distinctions between self-consciousness and the consciousness, say, of a small child or of a nonhuman animal. Baars's concept of self is the actual compilation of the multiple "contexts", the painstakingly assembled props and draping that decorate the stage for each individual. While such an analogy is fair enough, in itself it is not particularly helpful in progressing beyond the fairly obvious proposition that human individual experience will be flavoured, coloured and, in most cases, saturated by what has happened to that individual.
So what does the metaphor inspire? The overriding concept of a work space for coordinating and pacing brain processes, a small patch of sunlight amid the bump and grind of our otherwise automated grey matter. Consciousness, in Baars's vision, takes place within "working memory", a kind of mental short-list from which the final moment of consciousness transiently transpires. Again, however, as Baars himself discusses, the concept of working memory is far from new. Indeed, it is one of the multiple "functions" implicated in the operations of the prefrontal cortex, an area of human brain that, even compared with chimpanzees, has undergone astonishing expansion. How surprising, then, that Baars does not feel the need to refer in any detail to the effects of damage to this part of the brain and indeed to place his metaphor into a true neuroscientific context. Had he done so, his show might have had more meaning.
Lawrence Weiskrantz, on the other hand, is very clear about the need for maintaining a vigorous three-way interaction between theoretical/philosophical approaches, the neuroscientific probings into the physical brain itself and the cognitive data of neuropsychological experiments. While his meticulous documentation of neuropsychological experiments gives the book a reassuring infrastructure that is less obvious in Baars, there is a pay-off. The author often becomes so engrossed in his argument that, despite the good intentions of appealing to the general reader outlined in the preface, he frequently slips into complex terminology and frames of reference that would be tough going. The issue of, for example, the relevant anatomy and its interconnections, essential to understanding syndromes of brain damage, is further bedevilled by the jargon-ridden yet necessary complex experimental protocols performed by neuropsychologists as they dissect subtle, salient features from the morass of bewildering behavioural output from a disordered mind.
Like Baars, Weiskrantz starts with the reasonable assumption that an understanding of consciousness might grow from considering what differences might arise between conscious and unconscious processes in the brain. But instead of developing a model founded on metaphor, Weiskrantz lets the brain speak, via neuropsychological patients, for itself. Most emphasis is placed on the author's own field of study, namely amnesia and blindsight. The latter is a fascinating condition where patients deny seeing an object that they can nonetheless point out. In both conditions the damaged brain is still processing information, but that information cannot be used in conscious thought: in Baars's terminology perhaps, the props cannot be brought on the stage.
Weiskrantz's purported plan has been for nominally autonomous chapters, built around the separate questions of the whether, what, where and how of consciousness. Nonetheless, this book would be hard to dip into midstream: a clear theme starts to develop through the pages, namely the concept of the "commentary". According to Weiskrantz, the essence of consciousness is that of rendering some sort of ongoing account. But, reflecting his particular expertise, a "commentary" is viewed as something that can be experientially dissected and differentiated from a response that is a mere reflex or guess. While such studies do discriminate unconscious from conscious acts, and indeed in certain cases illustrate that nonhuman animals seem to be aware, the label "commentary" is of no obvious added value. Moreover, were the concept of a commentary to be a key one in understanding consciousness, it would be helpful to see it developed in relation to, say, the question of foetal and infant consciousness, as well as in the disruptions in consciousness that characterise schizophrenia and drug-induced psychosis.
The strength of Weiskrantz's account lies in the experimental data rather than in any illuminating new idea. Although excursions are made into evolution, it is clear the author's true interest is in the enormous potential of imaging techniques for insights into the differences between unconscious and conscious processes in humans. Surely if it were possible to view the areas of the brain active in a blindsight patient when conscious compared with when they were allegedly unaware of an object, the difference in images would constitute a giant step towards understanding consciousness, using scientific method in precisely the way Baars extols.
One turns the pages eagerly as Weiskrantz promises that just such a study is in fact in train. But the book proper ends before the key experiment is known: instead the results are finally unveiled as a postscript. This move is unfortunate for two reasons: first, this recent material is obviously included in the book with such haste that it resembles a highly detailed scientific paper. But interestingly enough Weiskrantz does mention in these final results that the prefrontal cortex could be important - the very area related to the phenomenon of working memory that featured with Baars. But, as with Baars, he attempts no scheme as to how this area, in concert with others, might be contributing to different types of consciousness. And the experimental bottom line, once finally discerned, is rather a letdown. Perhaps not surprisingly, no clear brain area emerges as a centre of consciousness, instead, there is a different configuration of working brain parts in conscious compared with unconscious conditions.
A second, serious problem is that these findings are subsequently revealed to be contested by another specialist in vision, Semir Zeki. This section disintegrates into a description of scientific bickering, where the reader will be left unclear as to the final outcome: are Weiskrantz's results definitive or not? It is surprising and disappointing, given that the book is geared to this type of key experiment, that the grand finale should end as a whimper rather than a bang.
But in any event, it could be argued that Weiskrantz would not have been biting the magic bullet of consciousness with the key imaging experiment: surely instead he would have been only establishing a further neural correlate, as electrophysiologists have before him, when they recorded combinations of structures electrically synchronous only during consciousness. How might these configurations of neuronal populations, yet not others, albeit defined by imaging or electrodes, provide a sufficient basis for consciousness? The other apex of the triangle, the philosophical/theoretical, remains terra incognita.
Both Baars and Weiskrantz attempt a scientific, cognitive approach and inevitably finish up with a somewhat circular description of consciousness as some sort of inner dialogue. At most, either account might inspire a possible neural correlate of consciousness, which neither author develops theoretically. Hence both fall between two stools: too experiential for a grand theoretical advance, and too abstract for detailed neuroscientific models. Both books deserve a place on the reading list, yet neither will preclude the probability that the list will continue to grow ever longer, nor the need for it to do so.
Susan Greenfield is professor of pharmacology, University of Oxford.
In the Theater of Consciousness: The Workshop of the Mind
Author - Bernard J. Baars
ISBN - 0 19 510265 7
Publisher - Oxford University Press
Price - £16.99
Pages - 193