Synaesthesia is the tendency to combine different senses – eg to see numbers, or hear sounds, as colours. It was described in 1880 by Francis Galton, but seems to have been largely ignored until recently, or regarded as a high level memory assocaition. (ie they didnt really see it, they just thought they did, probably becasue they were taking drugs…) However new techniques now allow scientists to see different patterns of brain connections in synaesthetes compared to others.
However, it seems it is a real effect.
Does it make any difference? The evidence seems to be that synaesthetes do it differently – ie one may see the number 3 as pink, another as purple. So its not as if there was a constant reality there that the rest of us dont see. (eg if we were all colour blind except for a few, those few would see colours consistently; but synaesthetes appear to embellish perceptions rather than add an extra dimension.) Neurophilosophyrefers to a limited trial, during which images drawn by synaesthetes in response to a particular piece of music were found, by non-synaesthetes, to be more appropriate than images drawn by non-synaesthetes, but I cant see much weight in this.
The UCL site says: “It would also be wrong to conclude that synaesthetes make better artists than non-synaesthetes (whatever the word better means in this context). Nevertheless, synaesthetes are able to draw upon a wealth of other experiences to influence their creations. David Hockney and Vladimir Nabokov are/were synaesthetes, and many other famous artists have been put forward as potential synaesthetes”
Another interesting exception: tetrachromats: people with four colour receptors in their eyes. (The standard assumption is that we have three – but as many as half of all women and a small percentage of men have four.) Ive yet to see any explanation of whether this makes a difference in what people see. (The brains interpretation of colour signals from the eyes is very complex, so its difficult to guess.)
It makes me wonder if the idea of auras, a subtle light that can apparently be seen around the human body by psychics, has any connection to these oddities of perception. Perhaps some people genuinely do see them. It might be interesting to test the brains of people who use Kilner goggles, invented in 1911 by the English doctor Walter Kilner, which some people claim allow non-psychics to see auras. Theres a long essay here about similar attempts to visualise the aura scientifically , though Ive no idea how authoritative it is. This also covers Kirlian photography.