Uta Frith sits in her beautiful, book-lined sitting-room in Harrow, north London, looking out towards the Chilterns. She is emeritus professor in cognitive development at UCL – and last year was made a dame. She is warm, smiling, bespectacled, dressed in brown linen and a fine gold necklace.Towards the end of our meeting, she describes a conversation she once had with an autistic person who was obsessed with light fittings in railway carriages and was trying to interest her in the minute differences between one fixture and the next. When she admitted she could not tell them apart, he laughed at her incredulously. People with autism are known to have an uncanny eye for detail and Frith has always been quick to acknowledge this and their other "cognitive strengths". But she has also been responsible for penetrating the particular difficulty autistic people have with "theory of mind" – the intuition about what is going on in another person's head. The light-fittings enthusiast would have been unlikely, for instance, to have entertained the possibility that his listener might not share his consuming interest.