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By Richard E Cytowic. Published by MIT Press, Cambridge, 2002, pp 424, £36.95. ISBN 0-262-03296-1
Synaesthesia occurs when an experience in one sensory modality or of a particular category (like a letter in black and white print) excites an experience in another modality or of another category (like a letter printed in colour). Such an inclusive definition allows many of us to lay claim to minor forms of the condition. But most of us clearly do not experience the remarkable cross modal sensations described in Cytowic’s fascinating book. The most common variety of classical synaesthesia is “chromesthesia”, the yoking of colour sensation to the perception of numbers, letters, words (these three triggers may be written, spoken, or both), musical and other sounds, smells, temperatures, pains, or emotions. But a host of other combinations is described: Cytowic has famously described a man who tasted shapes; someone tasted tunes; another was referred for counselling when she told the assistant principal of her school—ill-advisedly—that when she kissed her boyfriend she “saw orange sherbet foam”. One was so surrounded by spatial imagery, excited by everything from the alphabet to shoe sizes, that she explained “My entire life, everything, has a place that goes all round my body.” Synaesthetic experiences have certain common features: they tend to start early in life; they have often “always been there”; they are involuntary, triggered automatically by their stimuli; and they are durable and consistent, memorable, pleasurable, and usually spatially extended.
The greatest virtue of Cytowic’s work is his conviction that “a mental world exists” and his determination to describe it with his patients’ help despite the ineffable qualities of some of their experiences. His book is, also, a treasure chest of information about a miscellany of topics that might shed light on his main subject, from eidetic imagery through Kluver’s form constants to the role of metaphor in language and perception. If some parts of the book have the air of work in progress, it is a sign of Cyowic’s huge enthusiasm for a topic his writing has revitalised.