Synaesthesia is a fascinating phenomenon (or group of phenomena) in which stimulation of one sensory modality apparently leads to sensory experience in another modality (e.g. sounds producing visual experience of colour, as in the example that gives this book its name), but it has often been seen as a diverting curiosity rather than a subject deserving serious scientific study. In recent years this situation has changed and synaesthesia has attracted the attention of prominent psychologists and neuroscientists. Jamie Ward, a senior research psychologist at the University of Sussex, has emerged as one of the leading experts in the field, and has now written this short but compelling book, the first full-length ‘popular science’ treatment of the topic.

Ward begins with an entertaining survey of historical reports, before reviewing more recent work aimed at the elucidation of the mechanisms underlying synaesthetic experiences and the implications of this research for our understanding of sensory processes and perceptual awareness. The closing chapter is more speculative, as he ponders far-reaching questions around evolutionary psychology, language development and the structure of memory. These ideas are firmly rooted in what has gone before and do not feel contrived or excessive. Along the way, an extraordinary amount of work from experimental psychology and other disciplines (e.g. anthropology and linguistics) is used to bolster and illuminate the key arguments. Ward has mastered the art of popular science writing: the style is engaging and accessible throughout, and there is a coherent narrative flow as the ideas are developed. Those who have become wary of popular treatments of neuroscience will be gratified by the clarity of the author's thinking, which avoids or cuts through the simplistic reductionism and other conceptual confusions that often mar books on the brain. My only criticism is that the discussions of neuroanatomy might have benefited from being supplemented with simple schematic illustrations, but this is a minor point. The extensive notes and references (happily these are included at the end, rather than sprinkled all over the text) enable readers to explore further should they wish.

This is not a book about mental illness (as Ward stresses, there is no reason to view synaesthesia as a deficit or a diagnosis), but nevertheless it deserves a wide readership among psychiatrists. It is highly recommended to anyone with an interest in the science of conscious experience – a category that surely includes readers of this Journal.