Sounds like a rose to me

New Scientist, 31 March 2001

Synaesthesia: The strangest thing by John Harrison, Oxford University Press, 16.99, ISBN 0192632450

IT'S always a treat to stumble onto a book that promises to enlighten you about yourself. In Synaesthesia I found just that. Here's a book that investigates not just any old brain, but brains like mine, brains that have a weird and unexplained propensity to mix up senses.

For ten years now, John Harrison, formerly a neuropsychologist at the University of Cambridge, has been pondering what synaesthesia is all about. He's long been persuaded that the people telling him they hear words in colour or smell smells in shapes are not having him on. A "test of genuineness" he devised with colleagues confirms that a synaesthete who is asked which colour they associate with particular letters, words or numbers will give the same answer now as they did years ago.

I admire his respect for subjective reports, but it's the book's scepticism I enjoy most. Harrison examines historical figures who either claimed to have had synaesthesia or who had that honour bestowed on them by other people. He looks at, among others, poets Arthur Rimbaud and Charles Baudelaire, composers Aleksandr Scriabin and Nikolai Rimsky-Korsakov, and painters Wassily Kandinsky and David Hockney—all of whose creative works seem in one way or another to draw on synaesthetic associations. He stops short of saying they did not or don't have the condition—he can't know for sure—but he says there is not enough evidence. It could, he points out, be mere metaphor. Or even wishful thinking.

Synaesthesia, he says, isn't something that you suddenly acquire. It goes back as far as a person can remember. Although one synaesthete seldom agrees with another—even a relative—about the colour of a word or sound, a synaesthete's own take on it never changes. Apart from the apparent merging of the senses, there is nothing unusual about synaesthetes, apart from the fact that women outnumber men by about 9 to 1.

Harrison isn't easily convinced by theories purporting to explain the condition. His own theory is that neural connections we all have as infants, and which in most people are pared down, stay intact in synaesthetes. Even this doesn't seem to persuade him fully.

If there is a problem with the book, it is its balance. There is too much in the way of background explanation. Do we really need to be given crash courses in Mendelian inheritance, statistical significance and even the difference between psychoanalysts, psychologists and psychiatrists?

Elsewhere, though, I want so much more—especially more analysis. I would have liked more space given to the competing theories of what might cause the condition, and why they might be flawed. Intriguing theories shouldn't be summed up and dismissed in less than a page. How about more discussion on Peter Grossenbacher's idea that synaesthesia is caused by excessive "feed-backward" communication from brain areas now known to integrate multiple senses? And why not a better exploration of the suggestion that synaesthesia is no more than childhood associations "hard-wired" into the brain? Harrison does not mention other ideas at all: for example, that neighbouring brain areas responsible for colour, form and space may simply invade each other.

It's not that he is deliberately skimping on his competitors' theories to puff up his own. I want more of his theory and experimentation too. When he studies a synaesthete who is perfectly consistent over time in her descriptions of smell-induced shapes, he found absolutely nothing unusual in her brain scan. He doesn't even speculate about what this means.

And when he discusses how synaesthesia may be genetic, he suggests that the overwhelming preponderance of females must mean that the trait kills off males in the womb. Really? This harmless little condition could be fatal to my unborn male offspring? How? And what does it mean for the males who survive and have the condition?

If anyone could have sifted through it with a supremely critical eye, Harrison's the man. Sadly, he didn't. A hundred more pages, please.