Synesthesia: A Union of the Senses

Most people link senses only by way of metaphoric speech, saying, for example, that red is a "warm" color or that a certain cheese tastes "sharp." But a minority of individuals, known as synesthetes, experience the phrase "I see what you're saying" as literally true. In addition to studying the phenomenon for its own sake, neuroscientists are interested in what synesthesia might reveal about consciousness, the working of nonsynesthetic brains, subjective-objective relations, and the relationship between reason and emotion.

In this classic text, Richard Cytowic quickly disposes of earlier criticisms that the phenomenon cannot be "real," demonstrating that it is indeed brain-based. Following a historical introduction, he lays out the phenomenology of synesthesia in detail and gives criteria for clinical diagnosis and an objective "test of genuineness." He reviews theories and experimental procedures to localize the plausible level of the neuraxis at which synesthesia operates. In a discussion of brain development and neural plasticity, he addresses the possible ubiquity of neonatal synesthesia, the construction of metaphor, and whether everyone is unconsciously synesthetic. In the closing chapters, Cytowic considers synesthetes' personalities, the apparent frequency of the trait among artists, and the subjective and illusory nature of what we take to be objective reality, particularly in the visual realm.

The second edition has been extensively revised, reflecting the recent flood of interest in synesthesia and new knowledge of human brain function and development. More than two-thirds of the material is new.