From The Art and Popular Culture Encyclopedia
Synesthesia (also spelled synæsthesia or synaesthesia, plural synesthesiae or synaesthesiae)—from the Ancient Greek (syn), meaning "with," and (aisthēsis), meaning "sensation"'—is a neurologically based phenomenon in which stimulation of one sensory or cognitive pathway leads to automatic, involuntary experiences in a second sensory or cognitive pathway. While cross-sensory metaphors (e.g., "loud shirt", "bitter wind" or "prickly laugh") are sometimes described as "synesthetic", true neurological synesthesia is involuntary.
The word "synesthesia" has been used for 300 years to describe very different things, from poetry and metaphor to deliberately contrived mixed-media applications. It is crucial to separate artists using synesthesia as an intellectual idea—pseudo-synesthetes such as Georgia O'Keeffe who used such titles as "Music-Pink and Blue" — from those who had the genuine perceptual variety, such as Wassily Kandinsky or Olivier Messiaen.
The French Romantic poets Arthur Rimbaud and Charles Baudelaire wrote poems which focused on synesthetic experience, but were evidently not synesthetes themselves. Baudelaire's Correspondances (1857) introduced the Romantic notion that the senses can and should intermingle. Rimbaud, following Baudelaire, wrote Voyelles (1871) which was perhaps more important than Correspondances in popularizing synesthesia, although he later admitted ""J'inventais la couleur des voyelles!" [I invented the colors of the vowels!].
Synesthesia has been a source of inspiration for artists, composers, poets, novelists, and digital artists. Nabokov writes explicitly about synesthesia in several novels. Kandinsky (a synesthete) and Mondrian (not a synesthete) both experimented with image-music correspondences in their paintings. Scriabin composed color music that was deliberately contrived, whereas Messiaen invented a new method of composition to specifically render his bi-directional sound-color synesthesia. For example, the red rocks of Bryce Canyon are depicted in his symphony Des canyons aux étoiles ("From the Canyons to the Stars").