Neuroscientists have identified at least 54 types of synesthesia (e.g., unusual multisensory perceptions). It tends to run in families, suggesting a genetic origin. It is caused by increased cross-talk between various brain regions as well as extra connective pathways linking them together.
- Auditory: people hear sounds when they see things move or flash or experience taste when they hear music
- Time-space: people see things when they think about time, may perceive months of the year in circular shapes
- Mirror-touch: people experience sensations of touch when they see others being touched
- Visual: people perceive numbers or letters as having specific colors
(Macknik, Stephen L. PhD and Susana Martinez-Conde PhD. Sleights of Mind. p 100-108. NY: Henry Holt and Company, 2010.)
A linguistic psychologist (Julia Simner) at the University of Edinburgh is studying how conceptual thinking (not simply physical stimuli) may evoke colors and flavors in synesthetes. The meanings of wordscan produce the same flavors as their sound or written shape. (Mahony, Melissa. “Finding the Connection,” Scientific American Mind, October/November 2007.)