Steve Silberman says:
Perry Hall is a born synaesthete who "hears color and light, and created an iPhone/iPad app called Sonified to let his synaesthesia "loose in the wild, as he puts it. I take Hall's gift as a jumping-off point to talk about Nabokov's "freakish gift" for seeing letters in color, and several recent studies of color-grapheme synaesthesia and other forms of the phenomenon, including a kid with Asperger's syndrome who was inadvertently taught to see emotional "halos" around people's faces.
Inside the Mind of a Synaesthete