Some years ago the neurologist Oliver Sacks met an autistic child called Stephen Wiltshire. Like most autistic people, Stephen seemed to lack any real sense of an inner self. That meant that he had no idea that other people might have inner selves; he had, as cognitive psychologists would say, no theory of mind. This lack of mind theory makes it difficult for autistic people to communicate with others. The physical signals that most of us respond to intuitively, and that act as clues to what's going on in someone else's mind, mean nothing to them. They seem to be indifferent to other people's feelings. But Stephen had an extraordinary talent. Just as some musical idiots savants can play a piece of music note-for-note after a single hearing, Stephen was able to draw architecturally complex buildings from memory with total recall. These delicate and beautiful drawings were a best-seller when they were published as a book called Floating Cities in 1991. Talking to Stephen, Sacks was struck by the paradox of a person who had such prodigious gifts and such an apparent void within. So strange was this paradox that he asked himself if it was possible for a classically autistic person to be an artist in the conventional sense of the term. That set him thinking about the whole question of creativity.