Feynman had a neurological condition called synesthesia [1], which is when senses get mixed together in the same neurological pathway and you can "taste" a sound or "hear" a color. Which is very interesting since Feynman was said to have a "frightening" ease with equations, like an intuitive understanding of what they meant.

[1] http://en.wikipedia.org/wiki/List_of_people_with_synesthesia...