What is does it mean to hear music in colors, to taste voices, to seeeach letter of the alphabet as a different color? These uncommon sensory experiencesare examples of synesthesia, when two or more senses cooperate in perception. Oncedismissed as imagination or delusion, metaphor or drug-induced hallucination, theexperience of synesthesia has now been documented by scans of synesthetes' brainsthat show "crosstalk" between areas of the brain that do not normallycommunicate. In The Hidden Sense, Cretien van Campen explores synesthesia from bothartistic and scientific perspectives, looking at accounts of individual experiences, examples of synesthesia in visual art, music, and literature, and recentneurological research. Van Campen reports that some studies define synesthesia as abrain impairment, a short circuit between two different areas. But synesthetescannot imagine perceiving in any other way; many claim that synesthesia helps themin daily life. Van Campen investigates just what the function of synesthesia mightbe and what it might tell us about our own sensory perceptions. He examines theexperiences of individual synesthetes--from Patrick, who sees music as images andfinds the most beautiful ones spring from the music of Prince, to the schoolgirlSylvia, who is surprised to learn that not everyone sees the alphabet in colors asshe does. And he finds suggestions of synesthesia in the work of Scriabin, Van Gogh, Kandinsky, Nabokov, Poe, and Baudelaire. What is synesthesia? It is not, van Campenconcludes, an audiovisual performance, a literary technique, an artistic trend, or ametaphor. It is, perhaps, our hidden sense--a way to think visually; a key to ourown sensitivity.Cretien van Campen is a social scientist at the Social and CulturalPlanning Office of the Netherlands. He is the author of two books on perception andvisual art.