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17 September 2014
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Heather Birt's numbers are coloured, and she sees them arranged in space
Derek Tastes of Earwax

Questions and answers about synaesthesia.

Programme summary

Programme transcript

What is synaesthesia?
Synaesthesia is a condition, in which people's senses intermingle. Some synaesthetes experience colours when they hear, read or even think of letters and numbers. For others, words can trigger a real sensation of taste on their tongue.

There are numerous types of synaesthesia, and they can involve all senses - vision, hearing, touch, taste and smell. The most common form is colour-letter synaesthesia.

Do all synaesthetes have the same experiences?
Synaesthetes rarely agree on their colours or tastes. Even synaesthetic twins have different experiences. That said, recent research suggests there are certain overarching patterns, for example in colour-letter synaesthesia. For many synaesthetes A is red, and C yellow.

What causes synaesthesia?
Scientists agree that synaesthesia has a genetic basis, because it frequently runs in families. But an actual synaesthesia gene (or genes) has not been identified yet.

Additionally, environmental influences seem to shape each person's synaesthesia. The flavours people with taste-word synaesthesia experience are usually childhood flavours, not olives or coffee. And people with colour-music synaesthesia more often than not have had early musical training.

How do we know they're not making it up?
Synaesthetes have long been accused of making their experiences up. In the early 1990s, however, Professor Simon Baron-Cohen of Cambridge University noticed that synaesthetic colours don't change over time. If asked what colour is evoked by a letter or number, synaesthetes are incredibly specific and consistent at naming it - even if tested months or even years apart. This consistency was seen as a proof that synaesthesia is real.

Since then, scientists from across the world have designed tests to prove that synaesthesia is an authentic experience. The most compelling evidence, however, comes from brain scans. They show that colour processing areas in the brain light up when synaesthetes listen to words.

How common is synaesthesia?
Until recently, synaesthesia was regarded as rather uncommon, affecting only about one in 2,000 people. The latest scientific studies, however, have found that as many as one in 100 people is synaesthetic. This means, there may be more than half a million people in Britain with synaesthesia.

Is it a disease?
No, synaesthesia isn't a disease or a disability. In fact, most synaesthetes wouldn't even call it a condition, they prefer to refer to it as a gift. They couldn't imagine life without synaesthesia, and feel that people who don't have synaesthesia are losing out. But some forms of synaesthesia can be distracting. People for whom words evoke tastes, for example, can find their synaesthesia intrusive and upsetting at times.

Can drugs cause synaesthesia?
Drugs such as LSD, magic mushrooms or mescaline can indeed temporarily cause synaesthesia. That's why synaesthetes have long been accused of taking drugs. Interestingly, these drugs often have a much milder affect in people with synaesthesia than in people without the condition.

Are synaesthetes' brains different?
Synaesthetes' brains probably are different, but scientists have yet to discover what exactly goes on in the brain of a synaesthete. The current theories can broadly be divided into two groups. On the one hand, there are scientists who believe synaesthesia is due to extra nerve connections between normally separate brain areas. Others believe that synaesthetes don't have extra nerve connections, but that they use existing, normal connections in a different way.

Are we all to some degree synaesthetes?
Research has shown that we all may be synaesthetic to some degree. In various studies, people have been asked to match sounds with colours, and the results have shown that we all tend to associate lower notes with darker colours and higher notes with brighter colours.

Similarly, everyone seems to be quicker at manipulating smaller numbers with the left hand and bigger numbers with the right hand. This suggests that we all have what's called an implicit 'number line'. Number lines are common among synaesthetes; a lot of them actually see numbers arranged in space.

So even though most of us are not aware of it, everyone may have synaesthetic tendencies.

Are synaesthetes more creative?
There is anecdotal evidence that the proportion of synaesthetes among artists, poets and musicians is higher than among the rest of us. Some studies have also compared how well synaesthetes and non-synaesthetes perform in tests measuring creativity. They found that synaesthetes tend to do better at these tests. This has led some scientists to argue that synaesthesia and creativity may share the same brain mechanisms.

If creativity is about connecting unrelated ideas or concepts, and the cross-activations in the brains of synaesthetes affect more than just their senses, then synaesthetes may indeed find it easier to be creative. It's a plausible theory, but there's not yet enough scientific evidence to prove it.

Are synaesthetes better at maths?
Around 60% of synaesthetes who have coloured numbers also experience their numbers arranged in space around them. Being able to see such a number line can help them make quick calculations. Synaesthetes with very strong colours for their numbers, however, sometimes experience difficulties with maths. A lot of them complain: "How do you add up purple and yellow?"

Does synaesthesia tell us something about consciousness?
The problem of consciousness is one of the most puzzling questions in modern day science, and the study of synaesthesia may well offer insights. This is because synaesthetes may be experiencing an exaggerated version of something we all have.

If synaesthetes experience on a conscious level what happens in all of us on an unconscious level, then the difference between synaesthetes and non-synaesthetes may only be 'consciousness'. So if science can identify how the firing of nerve cells in synaesthetes and non-synaesthetes differs, we may have a pointer to understanding human consciousness.

I have synaesthesia. How can I get in touch with other synaesthetes?
The UK Synaesthesia Association organises newsletters, an annual meeting and a web-based discussion forum. For details of how to join, please see the link above on the right.

I have synaesthesia. How can I get in touch with a scientist?
The UK Synaesthesia Association liaises with scientists based at UK universities and holds a database of synaesthetes who are willing to volunteer for research. Alternatively, you may contact researchers directly but without any obligation. There are synaesthesia research groups based at University College London, the University of Edinburgh and the University of Cambridge. (See the link above on the right.)

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 Elsewhere on the web

UK Synaesthesia Association

University College London: Synaesthesia Research Group

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University of Cambridge: Faculty of Education: Synaesthesia and Education

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