Crossing the Chasm of Consciousness

Review of Conference:
Toward a Science of Consciousness Tucson 2002, Tucson, Arizona, April 8-12, 2002

Trends in Cognitive Science, 6, 276-277, 2002

(This is the version submitted, it may have been edited before publication)

Every other year the problem of consciousness brings together neuroscientists, philosophers, psychologists and assorted weirdoes for a week in Tucson, Arizona. Surrounded by the giant cacti of the Sonoran desert, this is the place to agonise about what has been called “The most important problem in the biological sciences” (Searle 1997, 3), and “the last surviving mystery.” (Dennett 1991, 21).

We should not underestimate the problem. While cognitive scientists unravel the details of visual processing, and scan brains at ever higher resolution, the mystery remains. How can the firing of objective neurons give rise to a subjective world? How can colour discrimination in the visual system produce the ineffable blueness of the Arizona sky, or the firing of neurons become the singing of birds. This is William James’s (1890) “fathomless abyss”, now more often called the Hard Problem or the explanatory gap. Nothing we learn seems to help us cross the chasm.

When it comes to explaining subjectivity, perhaps the most common assumption, though rarely explicitly articulated, is something like this. Our senses are constantly taking in information and building up a rich representation of the world; that representation is what we consciously experience at any given moment. In various fascinating ways this assumption took a beating.

The conference began with a whole morning on sensory substitution. From Paul Bach-y-Rita (University of Wisconsin), we learned that with a few hours of practice a congenitally blind woman could see and manipulate objects using a stimulating array on her tongue. With no training at all, one who had lost her vestibular system could stand and walk using feedback from a helmet, and one of the speakers was a blind woman who has laboriously learned to see using “soundscapes”; a scanning video to audio system. But is it really vision? She says it feels like vision, and can pin-point the time when it began to feel that way. The soundscapes do not interfere with her other hearing, and she even dreams in soundscapes.

That there is nothing intrinsically visual about the visual cortex was suggested by the results of Mriganka Sur’s (MIT), experiments in rewiring the cortex of newborn ferrets. Visual input was re-routed to what should have become auditory cortex, which was then found to be organised into maps and columns much like visual cortex. In other words, the characteristic organisation of different cortical areas may be driven by the input rather than being prewired or intrinsic. In discussion Alva Noë (UC Santa Cruz) suggested that even the chemical and membrane differences between auditory and visual cortex might be an effect of the type of input not a cause.

Noë challenged the usual assumption that any given neural activity must correlate with the same experience regardless of how that activity is produced. On the sensori-motor, or enactive, theory of vision this is not so (O’Regan & Noë, 2002). What makes an experience visual rather than, say, auditory, is not which neurons are firing, but how the system masters the sensorimotor contingencies involved. The basic idea is that vision is action, not representation, and seeing is a skill. This theory provides a challenging alternative to the usual representation-based, cognitive view of visual experience. It does away with the dualism inherent in representational theories and shifts the mystery to a new one – how action becomes subjectivity.

By contrast many other speakers assumed the more accepted view. For example Vittorio Gallese (Università di Parma) presented fascinating data on goal-related and mirror neurons in F5. In monkeys these neurons only fire when the object of the goal is visible, or the monkeys know it is present, whereas humans can respond to goal-directed actions with no seen object. Gallese discussed the idea of action perception as action simulation which furthers our understanding of the role of mirror neurons, and even hints at an enactive view. However, he characterised consciousness as a Phenomenal Model of the Intentionality Relation (PMIR); a kind of conscious mental model. This leaves the old problems of how internal representations comes to be subjective, or why some mental models are conscious while others are not.

Representational versus action-based theories reappeared in the session on machine consciousness. Ray Kurzweil presented an enjoyable series of speculations on the future of human immortality. According to his “patternism” each of us is a unique pattern in the brain that might soon be copied and downloaded into different machines. By contrast, Rodney Brooks explained how AI has moved away from centralised control and towards distributed behaviour-based systems that rely on leaving much of the information that they need right where it is, in the outside world. He showed an interactive robot, Kismet, in which apparently sophisticated social behaviours emerge from simple abilities with no central control and no central representations. In this case a visual attention system provides the coherence. Could we be systems like this? Could our sense of conscious unity really arise from a distributed system with no integrated mental model?

It doesn’t feel that way. Or does it? I urged participants to look harder into their own experience and try really believing in the results of change blindness experiments and enactive theories. Doing so can break up the habitual sense that we have definite “contents of consciousness” and that some representations are ‘in’ consciousness while others are ‘out’. Consciousness is not a container, I claimed.

Throwing out some basic assumptions may be necessary, but some of the theories explored at this conference are surely doomed to failure. Large-scale quantum coherence in cellular microtubules might seem to provide unity across the brain but how would these new quantum effects interact with ordinary, boring, neuron-size effects, and why does quantum physics explain subjectivity? Evidence of “presentiment”, or emotional responses occurring before an arousing stimulus is seen, caused much discussion, but are we really to reject the assumption that causes precede their effects?

In addition to the plenaries, the week included six parallel sessions every afternoon, poster sessions in the evenings and two days of pre-conference workshops. We learned about pure consciousness and the neural correlates of meditation, decision making, emotion, art, memes, sleep, drugs and time. Since the Tucson conferences began in 1994, consciousness has become a thriving multidisciplinary field. And it looks set to continue that way since we are still very far from crossing that chasm.


Dennett, D.C. (1991) Consciousness Explained. Boston and London; Little, Brown and Co.

James,W. (1890) The Principles of Psychology, London; MacMillan

O’Regan, J.K. and Noë, A. (in press) A sensorimotor account of vision and visual consciousness. Behavioral and Brain Sciences, 24

Searle, J. (1997) The Mystery of Consciousness. N.Y. New York Review of Books