Synesthesia is a condition where presentation of one perceptual class consistently evokes additional experiences in different perceptual categories. Synesthesia is widely considered a congenital condition, although an alternative view is that it is underpinned by repeated exposure to combined perceptual features at key developmental stages.
When I first heard about synesthesia, I thought it was a little hokey. But when I discovered it was real, I was fascinated – perhaps because I don’t seem to have much sensitivity in my individual senses. To have them multiply active – well – I am jealous.