Synaesthesia is an extraordinary condition in which the five senses intermingle. In the first of a two-part programme, Georgina Ferry discovers how it's changing our understanding of neuroscience and explores the world of synaesthetes who experience flavoured words or coloured letters, or see music as patterns and colours. The reader is Crawford Logan. EMAIL: radioscience@bbc.co.uk Producer Amanda Hargreaves Mind and body: page 42