Synesthesia

Do you see music? Can you hear letters? Do numbers or days of the month have personalities? Then you may benefit from the magical powers of Synesthesia, a neurological condition in which two or more bodily senses are coupled. The infamous author of Lolita,  Vladimir Nabokov was a famous synaesthesiest.

Forms include:

• A number form is a mental map of numbers, which automatically and involuntarily appear whenever someone who experiences number-forms thinks of numbers.
• experience colors in response to tones or other aspects of musical stimuli.
• individual letters of the alphabet and numbers (collectively referred to as graphemes), are "shaded" or "tinged" with a color.
• words and phonemes of spoken language evoke the sensations of taste in the mouth.

Visit the Museums of the Mind, a synesthesia portal by Dr. Hugo Heyrman, for more specific infomation on the interaction between art and synesthesia.

(Thanks to jimmyfeet!)

from Wikipedia:

Synesthesia (also spelled synæsthesia or synaesthesia, plural synesthesiae) -- from the Greek syn- meaning union and aesthesis meaning sensation . In a form of synesthesia known as grapheme → color synesthesia, letters or numbers may be perceived as inherently colored, while in ordinal linguistic personification, numbers, days of the week and months of the year evoke personalities. While cross-sensory metaphors are sometimes described as "synesthetic," true neurological synesthesia is involuntary and occurs in slightly more than four percent of the population (1 in 23 persons) across its range of variants (Simner et al. in press). It runs strongly in families, possibly inherited as an X-linked dominant trait. Synesthesia is also sometimes reported by individuals under the influence of psychedelic drugs, after stroke or as a consequence of blindness or deafness. Synesthesia that arises from such non-genetic events is referred to as adventitious synesthesia to distinguish it from the more common congenitalforms of synesthesia.