Imagine what the world would be like if numbers had specific spatial locations, music had shapes, or colours made sounds. Perhaps you’d experience the bass in the Jamie xx track Gosh as cuboid, metallic and heavy, with spiralling ribbons of synthesiser in the background.
This may sound bizarre, but it is actually reality for people with “synaesthesia”, a largely harmless condition that occurs in up to 20% of the population.
For a long time, synaesthesia was thought to be a neutral condition that offered no particular benefits or deficits. But we have now realised that there are in fact several cognitive and physiological features that go along with it – and some of them are very positive. Research today increasingly concentrates on what it is actually like to be a synaesthete and what we can learn from people with the condition.
We know synaesthesia is partly genetic, because it tends to run in families. But it is also thought to be environmental to some extent, because of the specific pairings between the senses. These are unique to each synaesthete, even those who are related to other synaesthetes.
Synaesthesia also appears to be associated with some immune-linked disorders, including multiple sclerosis, irritable bowel syndrome, and some kinds of headache. Current reasoning on this matter is that both synaesthesia and these immune disorders are underpinned by the same group of genes, but it’s not yet clear exactly how the two are related.
Given that synaesthesia is linked to these serious conditions, one obvious question is how it has managed to avoid being wiped out by natural selection. A possible answer is that it offers multiple cognitive advantages – and this is one reason that several groups of researchers have been attempting, over the past few years, to train synaesthesia-like associations in people who don’t have the condition.