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27 August 2015updated 28 Aug 2015 10:52am

The many shades of synaesthesia

Synaesthesia can be anything from seeing words in colours to full-on visual disturbances – and scientists are still learning why.

By Holly Baxter

Standing in a tent in a small market town in Wales, Berit Brogaard, a cognitive neuroscientist and professor of philosophy at the University of Miami in Florida, tried to convince an audience that a man could explain his rudeness towards a friend’s girlfriend: it’s a neurological condition. “This man – one of our subjects – has smell synaesthesia,” Brogaard explained. “His friend got a new girlfriend and she smelled like puke to him. He needed to avoid being in the same room.”

It sounds like an excuse but synaesthesia is a recognised and multifaceted condition. Its name refers to the stimulation of one sensory or cognitive pathway leading to the involuntary stimulation of another. Some people with the condition will associate letters with colours and argue that the word “Saturday” is bright yellow. Others will associate numbers with shapes, or sounds with textures. These aren’t imaginative quirks: research suggests that synaesthesia aids or even defines the cognitive processes of many unusually intelligent individuals.

Sometimes the condition is less a blessing than a curse. In May this year, during her presentation at the Hay-on-Wye philosophy and music festival How the Light Gets In, which I attended because I have grapheme-colour synaesthesia, Brogaard detailed some of the problems she has come across examining the lives of her subjects. “Take the example of a man who has sound-colour synaesthesia,” she said. “When he walks into a very loud room, or past a construction site, his visual field fills with colour, making him legally blind.” This man’s synaesthetic tendencies put him at risk virtually every day. Such sensitivity is fairly incompatible with modern life.

Nevertheless, synaesthetes are often dealt a fairly good hand. Brogaard’s research suggests that most people with the condition benefit from “improved memory, visual search skills, maths skills and creativity”. These don’t all necessarily occur in a single package, however. For instance, as a result of my grapheme-colour synaesthesia, I have only to see a word written down once to remember how to spell it for the rest of my life, yet my numeracy skills are woeful in comparison, as I am free from any associations between numbers and shapes.

The specific neurological causes behind the condition remain elusive. A traumatic brain injury – a car accident, a fall, or a sudden blow to the right part of the head – can sometimes cause synaesthesia to develop in previously unaffected adults. This was the case with Jason Padgett, a man who underwent brain scanning by Brogaard shortly after being beaten violently in 2002. As he recovered, Padgett claimed to see the entire world synaesthetically, in geometric shapes, allowing him to calculate any sum faster than a calculator.

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Brogaard has shown that the sudden death of neurons associated with a massive head injury can cause a spike in signalling chemicals elsewhere in the brain, which may account for the acquired ability.

Yet many are born with similar abilities without any obvious explanation. There is also reason to believe that savantism lies dormant in us all, waiting to be released by a well-timed head injury or brain abnormality.

It can come at a price, as demonstrated by “the real Rain Man” Kim Peek, whose lack of connections between the left and right hemispheres of his brain allowed him to read two pages of a book at the same time (one with each eye) but also led to debilitating social difficulties. Why some people have low-level tendencies while others become legally blind next to a construction site is something that neuroscientists are yet to discover.