The Brain David Eagleman

You will never think about your brain in the same way again.

A person with synesthesia might feel the flavor of food on her fingertips, sense the letter "J" as shimmering magenta or the number "5" as emerald green, hear and taste her husband's voice as buttery golden brown. Synesthetes rarely talk about their peculiar sensory gift — believing either that everyone else senses the world exactly as they do, or that no one else does. Yet synesthesia occurs in one in twenty people, and is even more common among artists.