Musical pitch classes have rainbow hues in pitch class-color synesthesia

Synesthesia, an anomalous blending of senses in which stimulation of one sensory modality produces sensation in a different modality, provides a unique opportunity to study how multimodal information is represented in the human brain. We investigated how pitch classes (do, re, mi, etc.) are associated with the three dimensions of color (hue, saturation, and value/brightness) in 15 subjects who possessed "pitch class-color synesthesia". Across-subject averaging of reported colors revealed that pitch classes have rainbow hues, beginning with do-red, re-yellow, and so forth, ending with si-violet, accompanied by a decrease in saturation. Enharmonic pitch classes that referred to the same pitch class with a different name produced color sensations according to the name of the base pitch class, e.g., a reddish color for do-sharp and a yellowish color for re-flat. Thus the main factor producing color sensations was the name, not the sound, of the note; behavioral experiments corroborated this interpretation. Pitch class-color synesthesia represents a newly described type of synesthesia that is distinct from the well-known crossmodal association between pitch height and value/brightness. Findings suggest that the two dimensions of musical pitch, pitch class and pitch height, are mapped to the hue-saturation plane and the value/brightness dimension of color, respectively.