Synaesthesia is a hereditary neurological condition that enables a person to experience multiple senses simultaneously. Hearing a D major chord may make a synaesthete literally see red. The number 5 could smell of banana.
The possibilities of synaesthesia have long fascinated both artists and philosophers. Painter Wassily Kandinsky, musician Alexander Scriabin and novelist Vladamir Nabakov were all probable synaesthetes and their creative breakthroughs merging sight and sound were likely connected to their atypical brains.