skip menus and go right to content



LifeWatch Employee Assistance Program




Topic Home  Related:  
Book Review - Synesthesia : A Union of the Senses
Synesthesia : A Union of the Senses
by Richard E. Cytowic
MIT Press, 2002
Review by Liam Dempsey
Oct 17th 2002

            To say that the phenomenon of synesthesia is interesting is to understate the point and Richard E. Cytowic’s second edition of Synesthesia: A Union of the Senses does the topic due justice.  This second edition involves more phenomenological accounts than did the first with additions and revisions made on the basis of new research into synesthesia and into human brain functioning and development generally.  The book begins with an introduction to certain historical issues, but quickly moves to a thorough and interesting discussion of synesthesia case studies in the second chapter.  Colored hearing and colored letters and numbers are the most common types of synesthesia (p. 7), but there are a wide variety of synesthetic experiences.  For subject TP, not only do letters and numbers have color, but music does as well; in other words, the auditory perception of music evokes color experiences in TP (pp. 25-26).  MT experiences letters and numbers not only as being colored but also as having gender and personality; the letter “M,” for example, is perceived to be blue-violet, male, and powerful (p. 297).  CSc, on the other hand, experiences involuntary tastes and smells while playing the piano or oboe.  Indeed, the tastes are sometimes so intense that they interfere with her musical concentration (p. 27).  DS sees anger not as red – as is the popular metaphor – but as purple.  “If I’m really upset at my kids and I’m yelling at them, there will be a purple background behind them” (p. 25).  MW perceives weight, shape, texture, and temperature when he tastes something with an intense flavor.  He describes the taste of spearmint, for example, as “cool glass columns” (p. 25).  Indeed, he utilizes these tangible sensory experiences in his cooking; so, for example, chicken must be cooked until it has the appropriate number of “points” (p. 6).   

The reader might be tempted to explain these sorts of reports in terms of a sophisticated use of metaphor.  After all, many of us would say that anger makes us “see red” or that certain sounds have certain “colors.”  However, as Cytowic makes clear, this is not a use of metaphor.  TP really does have color experiences that accompany his perception of letters, numbers, and music, and MW, tangible sensory experiences when tasting food.  The third chapter takes up the issue of the diagnostic criteria for synesthesia.  Most importantly, synesthetic experiences are 1) involuntary sensory experiences in one sense modality that accompany the stimulation of another, and 2) are consistent over time.  So for the synesthete, sensory stimulation in one sense modality leads to an automatic experience in another that is consistent and reproducible over her lifetime.

The fourth chapter looks at related neuropsychological phenomena, including the effects of certain drugs, release and sensory deprivation hallucinations, and the subjective experiences that often accompany temporal lobe epilepsy.  The fifth chapter – new to the second edition – takes up a discussion of spatial extension as it relates to synesthetic perception.  According to Cytowic, it is an essential element of synesthetic experiences that they are experienced as extended in space.  The synesthetic percept is taken to exist “out there” (p. 68) rather than in the imagination.  So, for example, if visual, it will be experienced as if on a screen in front of the subject’s face.  The sixth chapter considers the neural substrate of synesthesia.  Cytowic contends that the limbic system plays an important role in the binding the activities of the areas of the brain involved in synesthetic experience.  Cytowic here and elsewhere in the book emphasizes the extent to which synesthetic percepts are emotionally valenced.  The seventh chapter – new to the second edition – looks at developmental issues, including Daphne Maurer’s interesting, if controversial, claim that neonates are inherently synesthetic.  The penultimate chapter includes an interesting discussion of the personalities of synesthetes.  The areas of memory and mathematical reasoning as well as artistic and aesthetic expression, among others, are considered.  The book ends with a discussion of vision and color perception as they relate to synesthesia; specifically, Cytowic considers the theory of microgenesis – a theory that, among other things, challenges the conventional view of object representation as a building up of objects out of sense data (p. 342) – and how it may relate to hallucination, visual illusion, and, of course, synesthesia.

The critic will likely note the sometimes speculative nature of the discussion as well as the potentially controversial interpretation of empirical data.  Nevertheless, as a well written and comprehensive discussion of case studies, and past and contemporary research into the neurophysiological mechanisms that underpin synesthesia and related phenomena, Synesthesia: A Union of the Senses is useful both for the novice and advanced reader interested in consciousness, perception, and emotion. 


© 2002 Liam Dempsey


Liam Dempsey is a doctoral candidate (ABD) in the department of philosophy at the University of Western Ontario.  His interests include philosophy of mind  and the metaphysics of qualia, philosophy of psychology, and cognitive science.