What, ultimately, makes autistic people different? How do they experience the world? Twenty years ago no one had much of a clue. But a burgeoning body of research now suggests that the core of all autism is a syndrome known as mindblindness. For most of us, mind reading comes as naturally as walking or chewing. We readily deduce what other people know and what they don't, and we understand implicitly that thoughts and feelings are revealed in gestures, facial expressions and tone of voice. An autistic person may sense none of this.

Children with autism perform worse on tests of ascribing almost the full range of mental states (intentions, knowledge, pretence, deception, imagination, and so on). It is as if they suffer from a specific form of 'mindblindness'.