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When senses collide...

Anuttama Sheela Mohan

Synaesthesia is a condition where the various senses intermingle. While some people attribute colours to represent numbers or alphabets, others taste words or shapes.

The great composer Franz Liszt often confounded his orchestra with commands such as, "O please, gentlemen, a little bluer, if you please! This tone type requires it," or "That is a deep violet, please, depend on it! Not so rose". At first the musicians thought that Liszt was being facetious, but soon realised that he actually perceived colours where, for them, there were only notes.

Liszt's condition is one shared by thousands — synaesthesia. The word comes from the Greek `syn' (union), and `aesthesis' (sensation) and refers to an intermingling of the senses.

Synaesthesia can take many forms. Colour-grapheme synaesthetes experience letters or numbers printed in black-and-white in colour. Physicist Richard Feynman experienced this form of synaesthesia. In his own words: "When I see equations, I see the letters in colours — I don't know why. As I'm talking, I see vague pictures of Bessel functions from Jahnke and Emde's book, with light-tan j's, slightly violet-bluish n's, and dark brown x's flying around. And I wonder what the hell it must look like to the students."

Others literally "taste" shapes or words. In Syn, a new magazine developed for synaesthetes and those interested in synaesthesia, Teresa Tickner describes how for her the word sacrifice tastes of liquorice; witch of a lettuce and egg sandwich; and scrupulous of steak and chips.

For such an intriguing phenomenon, synaesthesia has received surprisingly little serious scientific attention until very recently. Often synaesthetes were dismissed as madmen (or, more likely, madwomen, as the condition is six times more common in women). Even today, there are many synaesthetes who are unaware that they are in any way different from the `normal' being.

Francis Galton could be credited with introducing synaesthesia to the scientific community in the late-1800s. He was profoundly interested in the power of visualisation or of forming pictures of objects in the mind's eye.

Galton presented the vivid and detailed first-hand accounts of many synaesthetes in papers published in Nature and the Fortnightly Review. He devoted much of his attention to what he called "number forms" in which numbers are experienced as having a spatial form, sometimes coloured.

Today number forms are considered a special case of "sequence form" synaesthesia, where sequences are perceived as having a particular spatial form (with or without colour). These sequences might be numbers, days of the week or months of the year.

At the Center for Brain and Cognition, University of California, San Diego, V.S. Ramachandran and his student Ed Hubbard are conducting research into the phenomenon of synaesthesia, especially sequence forms and colour-grapheme synaesthesia.

To show that colour-grapheme synaesthesia has a genuine sensory basis, they used a `pop-out' test. This works on the premise that when objects are differently coloured they tend to pop-out. For instance, when shown a set of identically coloured 2s in a field of 5s, normal subjects must observe the numbers one-by-one to find the 2s. For synaesthetes, the 2s, being differently coloured from the 5s, tend to pop out.

Perhaps what's significant about their work is how seemingly simple experiments can have such far-reaching results. In one intriguing experiment, they show synaesthetic volunteers Roman numerals to see whether they too elicited colours. While the majority did not see the Roman numerals in colour, there were some who did.

How can one explain this difference? Ramachandran and Hubbard assume that synaesthesia is caused by "cross-wiring" between the regions of the brain responsible for processing different kinds of sensory signals.

Work in the area of synaesthesia is likely to not just expand our understanding of this fascinating phenomenon, but also promises to have a profound impact on our understanding of the working of the human brain.

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