Pupil size in people with synesthesia changed depending on how bright or dark the perceived colors were.

Some people experience a crossover in senses. Known as synesthesia, it can manifest as "seeing" music in colors, or "tasting" words. Typically thought to be fairly rare in the general population, ...

Synesthesia is an extraordinary neurological condition in which a person simultaneously and involuntarily perceives one sense with another. There are an estimated 35 types of synesthesia that people ...