In Britain, a team of psychologists has begun to tease out a biological explanation for synaesthesia. They are using hundreds of volunteers who claim to feel, see and smell 'in colour'.
Simon Baron-Cohen, a clinical psychologist at London University's Institute of Psychiatry, says doubts about synaesthesia being a genuine condition have been largely dispelled. 'The evidence is accumulating that it is real, so we're taking it seriously after a history of it not being taken all that seriously in this country.'
Studying people who have synaesthesia will help scientists understand more fully how the brain is organised, Dr Baron-Cohen says. One theory is that babies are born with senses that are intermingled, but within a few months their brains begin to separate them. 'Synaesthesia may be showing what happens when this modularity is not achieved,' he says.
The team at the Institute of Psychiatry began its research after making contact with Elizabeth Pulford, an 82-year-old artist who had advertised herself in the British Psychological Society's Bulletin as 'a woman who has experienced the lifelong condition of hearing words and sound in colour'. After a series of controlled tests on her, the psychologists were convinced she really could see words in vivid colours. Mrs Pulford was given 100 words and asked to ascribe a precise colour to each one. A year later she was given the same test and was able to give exactly the same description to each word. 'Moscow', for instance, was a darkish grey with spinach green and a pale blue in places; 'Daniel' was deep purple, blue and red and shiny; 'Maria' was deep violet-blue.
Dr Baron-Cohen and his colleague John Harrison of the Charing Cross Medical School in London have now begun to investigate the first batch of about a dozen of the 600 people who have since contacted them claiming to have synaesthesia. He said that some appear to have a primitive form of the condition where they only see days of the week or months of the year in certain colours. Others have a much wider ability to associate a large vocabulary of words with a spectrum of colours. 'The descriptions we've been given are so detailed and consistent that it is difficult to explain by either a metaphorical use of language or by an impressive memory,' Dr Baron-Cohen says.
Dr Eraldo Paulesu, at the Medical Research Council's Cyclotron Unit at the Hammersmith Hospital, London, has helped the researchers find the possible fundamental biology behind synaesthesia. When volunteers were placed in a scanner to measure blood flow in different parts of the brain they were found to have unusual activity in the visual cortex when words or sounds were played over headphones. 'This was not so in people without synaesthesia,' Dr Baron-Cohen says.
About 95 per cent of those who have come forward are women. The trait seems to run in families, although the link is not very strong. People with synaesthesia are also convinced that they dream in colour, whereas other people think they only sometimes do so.