Some researchers now argue that sensory substitution shares characteristics of, and is an artificial form of, a neurological condition called synesthesia, in which sensory information of one type gives rise to percepts in another sensory modality.9 For example, the physicist Richard Feynman was a grapheme-color synesthete, for whom each letter of the alphabet elicited the sensation of a specific color, so that he saw colored letters when he looked at equations. The artist Wassily Kandinsky had another form of synesthesia. He experienced sound sensations in response to colors, and once said
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