"Consciousness" used to be a taboo word among scientists: the problem was just too intractable. Now it is becoming a buzz word.

"Tucson II", the second "Towards a Science of Consciousness" conference following one in 1994, opened here on Monday. Over 1,000 delegates queued to register outside the massive music hall under the hot Arizona sun - and that is not including the thousands of "virtual delegates" all over the world following the conference as it unfolds in text and sound in the pioneering THES Internet coverage (address, page 2).

There is an astonishing range of nationality and discipline among the delegates, even in these interdisciplinary days. Postgraduate students in the cognitive sciences and philosophy rub shoulders with retired professors of physics who say that they have been interested in the problem of consciousness for, hmm, a long time. Plenary speakers from the United Kingdom include mathematician Roger Penrose, psychologist Colin Blakemore and pharmacologist Susan Greenfield, all from Oxford. The UK is the biggest source of both delegates and speakers after the US.

Diversity and interdisciplinarity were stressed in the opening speech by the chairman of the scientific programme committee, Stuart Hameroff, an anesthesiologist at the University of Arizona who is working closely with Professor Penrose. "We want a spectrum of approaches brought to bear on the problem - reductionism, materialism, philosophy, cognitive neuroscience, mathematics and physics and also phenomenological approaches ranging from introspection and aesthetics to parapsychology."

³ÉÈËVRÊÓƵ

He announced that the University of Arizona is trying to set up a centre for consciousness studies. If negotiations with the potential backers are successful, postgraduate students will be taken on by the centre to carry out research in five fields: philosophy, neuroscience, cognitive science, quantum physics and cultural perceptions of consciousness.

But Professor Hameroff admitted the existence of many sceptics. The early 1970s were an exciting time in neuroscience and led to the formation of a society with members from molecular biology, chemistry, neuroanatomy, neuropharmacology and neurosurgery. Now the society's annual meetings attract 25,000 delegates. "They are just too big," said Professor Hameroff, who has stopped attending them.

³ÉÈËVRÊÓƵ

Another possibility is that consciousness studies will fizzle out for lack of progress. As Colin McGinn, a key figure among philosophers of consciousness, said in The THES last week: "The only way to avoid being checkmated by consciousness is to assume you do not understand it."

Professor Hameroff is more hopeful: "There is a lot of interesting work going on, some of which I think will coalesce. There is a high motivation - one mustn't forget that the consciousness question is the most interesting question there is. That's not just my view but probably the view of everybody at this conference."

If delegates can agree on that, they can also agree, pretty much to a man and woman, that philosopher Daniel Dennett was a bit presumptuous in calling his recent bestselling book, Consciousness Explained. In the opening plenary session, philosopher David Chalmers - very young and with very, very long hair - author of the latest attempt to explain consciousness, The Conscious Mind, had an entertaining spat with the bushy-bearded, charismatic Professor Dennett, who is now something of an elder statesman in the field. Professor Dennett said, to general laughter, that he used to think he was a radical but Tucson had made him realise he was a conservative. "Now I know what it must have felt like to be cop at Woodstock, saying 'smoke anything you like as long as you don't hurt anyone'."

For Professor Dennett believes, fundamentally, that "straight" science is already capable of explaining consciousness and will in due course construct conscious machines, there is no need for "alternative" approaches.

³ÉÈËVRÊÓƵ

In the words of MIT's Danny Hillis, another plenary speaker: "People have a strong intuition that machines cannot be conscious, not because they overestimate how wonderfully complex the human mind is, but because they underestimate how complex machines are." In Professor Hillis's view, using new programming techniques arising from existing techniques in evolutionary programming that incorporate aspects of Darwinian natural selection, machines will be "bred" to address specific problems over thousands of generations. Analysis of the final design will show that it cannot be broken down into simpler components, in contrast to conventionally engineered artefacts.

Jeffrey Gray, from the Institute of Psychiatry in London, another plenary speaker, is unconvinced. He is working on synaesthesia, the condition of "coloured speech". Synaesthetic individuals give colours which they experience on hearing a certain word. In one subject, the word "Maria" triggered a dark purple colour with a shiny texture and speckled spinach-green at the edges. When this subject was tested on the same word list and without warning a year later, she was 100 per cent consistent in the colours she described for each word.

Professor Gray and his team are examining the brains of subjects with a technique called functional magnetic resonance imaging. They hope that if the special features of coloured speech are due to "hard wiring" between normally separate sensory modes (hearing and vision) this will show up clearly in these experiments. "If correct," says Professor Gray, "this inference would further imply that much current effort to explain consciousness by reference simply to informational transactions that go on in nonneuronal systems, such as computers, is misdirected."