Some people hear colors, see flavors and are generally prone to a mixing-and-matching of typically disparate perceptual domains.

Those people are called synesthetes, and were the topic of a World Science Festival talk delivered last night by neuroscientist extraordinaire V.S. Ramachandran.

Where does synesthesia come from? Maybe synesthetes are just lying. Perhaps they're under the influence of hallucinogenic drugs – many research subjects are college kids, after all – or happened as children to play with colored alphabet blocks. Or maybe they're simply good with metaphors.

To Ramachandran, the latter answer gets at the truth – but he stressed that what appears as metaphor is a literal sensory experience for synesthetes. That may explain, he said, why synesthesia is eight times more common among poets, artists and novelists than the general population.

The essence of art is, arguably, metaphor, and its practitioners are especially prolific – and metaphor is just a convenient shorthand for the connection of unlinked cognitive phenomena. That's exactly what appears to happen in the minds of synesthetes. Far-flung parts of their brain have unusually high levels of cross-wiring.

For people of a poetic bent, this is quite useful: You get to tell your date that her eyes glow like the moon, hair ripples like the ocean and skin is smoother than a friendly corporate takeover. (Fine, I'm not a poet.) But life wasn't always so romantic. The arts are a latter-day human characteristic, one that requires a certain amount of security and stability to flourish.

So how did it develop? To help our ancestors climb trees, said

Ramachandran. Doing so requires a vision-informed mental map of the branches before us, as well as a touch-informed mental map of our limbs' positions. Somehow these have to correlate. Which is quite a trick, when you think about it.

Once early primates pulled off that feat of abstraction, it wasn't long

\– evolutionarily speaking – before we were drawing on cave walls and whispering sweet nothings and holding Shakespeare revivals.

But just because you don't have the urge to eat the color purple doesn't mean you're not a synesthete.

"We are all synesthetes, to some extent," Ramachandran said, then administered this handy test to the audience: Look at the shapes in this picture.

Imagine that one is named "kiki" and the other "booba". Which is which?

If the shape at right strikes you as kiki and booba's at left, then you've got some synesthesia going on, said Ramachandran. To most of us, the jaggedness of the shape on the right corresponds to the abruptness of the phonemes in kiki, while the shape on the left resonates with the rolling vowels of booba.

But wait – does the sharper shape look like a booba to you? Well, that doesn't necessarily mean you're incapable of metaphor. But just to be on the safe side, you might want to avoid strenuous tree-climbing.

Image: V.S. Ramachandran, kiki and booba. Apologies for the blurriness – my camera doesn't deal well with low light.

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