For a 22-year-old woman known as AW, denim evokes feelings of depression, disgust and worthlessness. Corduroy causes confusion, and silk provides utter contentment. She is one of two people known to experience a newly discovered form of synaesthesia, where textures give rise to strong emotions.
HS, another young woman who experiences tactile-emotion synaesthesia, gets no kick out of denim. Fleece and dry leaves disgust her, while the touch of tennis balls, fresh leaves and sand are heaven.
Other forms of synaesthesia include numbers and letters that evoke colours, shapes that evoke tastes shapes and colours with their very own fragrances.
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AW and HS鈥檚 sensations, unusual though they may seem, are an extreme form of the positive feelings most people associate with a soft blanket or the aversion to sharp knives and jagged rocks, says , a neuroscientist at the University of California, San Diego.
鈥淲e have an affinity for fur because when were evolving in the ice age, we needed coats,鈥� he says. 鈥淭his is the architecture on which [tactile-emotion synaesthesia] is built.鈥�
Real metaphors
A mental mishmash between touch and emotion could underlie metaphors such as sharp criticism and a rough night, he says. 鈥淪ynaesthesia is a quirky example of a mechanism we all have for generating metaphors,鈥� he says.
Ramachandran 鈥� one of the first researchers to apply neuroscience to synaesthesia 鈥� and colleague David Brang tested and retested AW and HS to confirm that their experiences were bona fide.
Measurements of skin conductance 鈥� sweat 鈥� suggest that touching denim and fleece truly evoked instinctual responses of disgust in AW. While surreptitious video footage of AW and HS caressing different textures point to the same conclusion: tactile-emotion synaesthetes associate strong, irrepressible feelings with touch.
Their associations proved consistent, too. On AW鈥檚 first examination she said fine-grained sandpaper was like 鈥渢elling a white lie鈥�. Eight months later, upon touching the same sandpaper, she felt 鈥済uilty, but not a bad guilt鈥�. Soft leather made HS鈥檚 skin crawl on a first visit. On a subsequent occasion it made her feel afraid and repulsed.
Silver lining
Both women have developed ways to cope with their experiences. When AW touches an aversive texture, she sings to distract herself from it. Feeling something made of silver 鈥� a positive texture 鈥� can also cancel out unpleasant tactile-emotions. The same trick helps her feel better after a bad day.
Now that Ramachandran and Brang have confirmed that tactile-emotion synaesthesia is a genuine experience, they are hoping to discover what is going on in the brains of AW and HS.
A more common form of synaesthesia, where numbers are linked to colours, results from cross-wiring in the brain areas responsible for detecting colour and processing numbers, Ramachandran says. 鈥淭hose neurons, those connections, have been not pruned away. They are residual and excessive,鈥� he says.
Interfering neighbour
Ramachandran theorises that tactile-emotion synaesthesia is caused by similar cross-wiring between the insula cortex, the seat of many emotions, and its close neighbour, the somatosensory cortex 鈥� a region responsible for processing texture.
鈥淲hatever鈥檚 going on with these synaesthetes, it seems to be an example of the normal mechanisms that are present in all of us,鈥� says Edward Hubbard, a neuroscientist at Cornell University in New York. He reckons that HS and AW鈥檚 associations between texture and emotion are not learned but are hard-wired and mostly arbitrary.
鈥淚t鈥檚 the sort of randomness that gets wiped out, trained way, overwhelmed by learning and cultural factors鈥� in most people, but not in synaesthetes, he says.
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