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BODY AND MIND: Can you feel the guitar sound on your ankles?: WEIRD SCIENCE: The experiences of synesthetes, who are often dismissed as having vivid imaginations, could tell us new things about perception, findsJerome Burne
Financial Times; Jan 6, 2001

What is the colour of five? What does it feel like to taste mint? What is the sound of blue?

To most of us such questions are either meaningless orsuitable only for adrama workshop. But for a small proportion of the population - possibly one in 2,000 - these are questions towhich very precise answers can be given. Five, for example, is lime green, the sound of guitars is like someone blowing on the ankles, while a torn ligament can turn everything orange.

If such responses make sense to you, then you have synesthesia - meaning, literally, joined sensations - an extraordinary condition that causes certain senses to "leak" into one another.

Some synesthetes revel in it. "To me it's like you guys see the world in black and white," says one, who sees every letter, number, sound and pain in colour. Others learn to keep it a secret after the funny looks they received trying to discuss it in childhood. But to neurologists investigating the brain it is a boon.

"When scientists study normal perception," says Daniel Smilek, of the University of Waterloo in Ontario, Canada, "because we see in the same way, there are lots of things we take for granted. Synesthesia can tell us new things about normal perception because it's abnormal."

It shows that people all around us may have very different experiences of the world. Some researchers believe it may even offer a unique window in that ultimate neurophysiological mystery - the nature of consciousness.

The English philosopher John Locke was the first westerner to describe synesthesia. He wrote about a man who experienced scarlet as the sound of the trumpet. Later, the condition excited the imagination of fin de sie`cle Romantics, such as Wassily Kandinsky, who believed synesthetes were closer to God and were "like good, much-played violins, which vibrate in all their parts and fibres". But it proved impossible to research and interest waned. Recently, however, advances in brain imaging have sparked renewed interest.

Early claims that the multi-sensory experiences of synesthesia were linked with the hallu cinations of schizophrenia, have long been disproved. However, synesthetes are supposed to be more prone to unusual experiences such as deja` vu, and precognitive dreams, as well as having mathematical abilities below average.

Until 1993, many researchers dismissed it as another name for a vivid imagination, but then an experiment by Simon Baron-Cohen, of Cambridge University, showed that synesthetes, who, when tested, linked particular colours or shapes to letters, gave the same answers in 92 per cent of instances when tested again a week later. Non-synesthetes, given similar examples to imagine, returned the same answers in only 37 per cent of instances.

Synesthesia goes beyond normal association or metaphor. You are not synesthetic if a square reminds you of squealing tyres, but you are if you actually hear the squeal.

Although there is some overlap between synesthetes as to what colour is linked to what - 56 per cent see the letter "o" as white - most of the responses are individual. There are 30 possible sensory combinations, but links between sounds and colours are the most common. Women are between two and eight times more likely than men to have the condition.

As yet there is no explanation for any of this, but small pieces of the jigsaw are emerging. A brain scanning experiment by Baron-Cohen in 1995 found, perhaps not surprisingly, that when synesthetes were listening to words, areas of the brain that are normally only active in response to vision and colour, blinked on.

From this comes the notion that we may all have synesthesia at birth, when many parts of the brain are linked, but, as we develop, connections are pruned, so our senses become islands. Somehow, synesthetes have kept their synaptic bridges intact. It's an idea that has been challenged, however, on the grounds that if you give people enough psychoactive drugs, such as LSD, they will have synesthetic experiences, which suggests the mechanism is intact but repressed.

Synesthesia raises all sorts of big questions about how we create an internal representation of the world, but scientists have to break these down into smaller and more manageable ones. For example, is the synesthete's colour response to a number 5, say, triggered by the sight of 5 on the page or just the idea of 5? Earlier this year, the neurologist Vilyanur Ramachandran of the University of California, San Diego, came up with a test for synesthesia which seemed to suggest it was the sight of the number that was important.

You look at a page made up of specially drawn 2s and 5s that are a mirror image of each other. The 5s are placed at random but the 2s form shapes such as circles or triangles. To a normal person they just look like a jumble, but to asynesthete the patterns made from 2s leap out as a different colour from the 5s. "This shows they were really sensing colour," says Ramachandran. "Concepts don't group."

But then last summer psychologists at Waterloo University came up with evidence that what really matters is the concept of a number.

Smilek and his colleagues gave a synesthete some simple mental arithmetic to do while looking at different coloured sheets. They found that when the colour of the sheet clashed with the colour of the answer, her response was slower than when it was the same. An actual colour could interfere with the colour of a number that existed only in her head.

"Our research suggests that colour experiences coincide with the processing of meaning," says Smilek. "It's the concept of a number that's coloured."

So which is it? At present, we don't know, but somewhere down the line the answers to dozens of such questions might allow neurologists to explain what's going on in the brain to produce such sensory symphonies as those experienced by the author Vladimir Nabokov: "The long 'a' of the English alphabet has for me the tint of weathered wood, but a French 'e' evokes polished ebony. This black group also includes hard 'g' (vulcanised rubber) and 'r' (a sooty rag being ripped)."

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