SYNAESTHESIA, the phenomenon in which the senses are mixed up and people link, say, tastes with musical notes, comes in at least two different flavours.
Edward Hubbard and his colleagues at the University of California, San Diego, put six people who associate letters and numbers with various colours through a series of experiments, comparing them with six controls. In one of the experiments, known as the 鈥渃rowding task鈥, volunteers have to pick out a particular letter or number from a jumble of others.
The more letters in the mix, the harder it is to pick out the target. If different letters have different colours, however, identification speeds up. The researchers wanted to know if synaesthetes鈥 innate sense of colour would help them with the task even though the letters were in black and white.
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They discovered it did, but only in those who see the associated colour projected onto the letter or number. The others, who merely perceive the associated colour 鈥渟omewhere in their head鈥, performed no better than non-synaesthetes. Brain scans also revealed differences: the brain鈥檚 colour centre was more active in those who excelled at the crowding task (Neuron, vol 45, p 975).
Synaesthesia is thought to be due to 鈥渃ross-wiring鈥 in the brain that links up different senses. The differences between these two kinds of synaesthesia might reflect the different kinds of cross-wiring. 鈥淭here are multiple stages of colour processing,鈥 says Hubbard, 鈥渁nd the cross-activation may be occurring at different stages.鈥
The team suggest there may be 鈥渉igher鈥 synaesthetes, for whom the mere concept of a letter or number conjures a colour, and 鈥渓ower鈥 synaesthetes, who have to see the letter or number to conjure up any colour sensation.
