Doctor's Review: Medicine on the Move

December 6, 2021


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Blending of the senses

Synesthetes hear music and taste food in colour and there are more of them than you might think

Imagine a world where letters and numbers have colours, where music takes forms, or names are accompanied by taste. This is the wonderful world of synesthesia, a neurological phenomenon that mingles senses together. Maligned through much of history as a freakish disorder, synesthesia has, in recent years, been much more widely understood and is now even celebrated.

“It’s not a disorder,” says well-known neurologist and author Richard Cytowic. “It’s a trait, like having blue eyes.” Not only is there nothing wrong with the synesthetic mind, it is in fact likely to possess a heightened capacity for memory and recall. And since sight, sound and movement already map to one another so closely, says Cytowic, there’s a little bit of synesthesia in all of us.

What’s the difference between someone who occasionally has an experience of one sense that triggers another — “This syrup tastes pink!” — and a real synesthete? Somewhere between two and four percent of the population is made up of synesthetes in which synesthetic associations are conscious, distinct, automatic and constant over time. If an oboe has a mahogany-coloured sound, it always will. If the letter Q is turquoise, it will remain so for a lifetime, though another synesthete’s Q could be orange or green.

Seeing like Nabokov

The Russian writer Vladimir Nabokov described his letter A as having “the tint of weathered wood,” R as “a sooty bag being ripped” and the letter S as a “curious mixture of azure and mother-of-pearl.” He mused on his “oatmeal N, noodle-limp L, and the ivory-backed hand-mirror of O,” steely X, thundercloud Z and huckleberry K, as well as what he calls “the green group” of alder-leaf-F, the unripe apple of P and pistachio T” (Speak Memory, 1966).

Nabokov was not the first writer to provide vivid colour imagery for letters. The French Symbolist poets were the original artist-types who found the concept of synesthesia sexy. The earliest traceable medical reference to coloured hearing — “seeing colours upon hearing musical notes” — can be found in an 1812 thesis by a German physician who went simply by the name of Sachs. The father of 19th-century French poet Charles Baudelaire had an extensive collection of medical textbooks and there’s speculation that son Charles may have stumbled across this, or some similar reference, and been propelled into the flurry of inspiration which produced his famous poem Correspondances about the romantic intermingling of the senses.

In 1871, the same year that Gustav Fechner, the father of psychophysics, made records of 73 patients who reported having coloured letters, Arthur Rimbaud, Baudelaire’s contemporary, published his famous poem Voyelles. In it he declares that A is black, E is white, I is red, U is green and O is blue. Though he has since been understood not to be a true synesthete, Rimbaud can be credited with popularizing the condition among the artist community of the day.

Fading colours

The font of inspiration which artists, musicians, writers and researchers alike found in the exploration of synesthesia dried up with the rise of behaviourism in psychology when any mention of internal subjective experiences was verboten. More than 600 papers on the subject were published before 1940, but from 1940 to 1975, there were only 12.

Synesthesia’s long lapse into obscurity meant that by the mid-1960s when people with blended sensory associations reported seeing sounds and tasting colours they were deemed “pot-heads and junkies” or were thought to be victims of excessive use of LSD. But by the 1980s, as the cognitive revolution encouraged the study of consciousness, synesthesia experienced a renaissance that has been gathering momentum ever since. That said, knowledge about the neurologic basis for synesthesia remains scant. The trait has been observed to be more prevalent in women, left-handed people, those on the autism spectrum and artists. The term synesthesia — from the Greek for “the joining of senses” — is derived from the theory that the brain is firing two senses at once. Unlike most brains, which engage in the developmental process of pruning, the standard theory has it that synesthesia is caused by increased connectivity between adjacent brain regions which failed to prune normally.

Recent researchers have reframed the subject by suggesting that it isn’t a sensory perception which causes a colour association at all, but rather the meaning that we assign to that perception. They suggest the term “ideasthesia,” meaning “sensing ideas” would be more accurate. In the past, colour associations were thought to be entirely random misfirings of the brain. This new way of understanding the phenomenon sees the associations between letters, numbers and colours in early childhood as a way for the forming brain to remember abstract concepts by anchoring them in familiar experiences. Tests which show that colour associations shift according to context — for example, an “S” shape will be perceived as having a different colour depending on whether it’s viewed as the letter ’s’ or the number 5 — confirm that the process is conceptual and not perceptual.

Fisher Price power

An amusing discovery was made in 2009 about early childhood and the formation of synesthetic associations with alphabet colours. Two Stanford scientists, Drs Nathan Witthoft and Jonathan Winawer, observed a distinctive pattern in one synesthete’s letter colours, a particular cycling through red, orange, yellow, green and blue. When asked about it, the synesthete pointed out a match between those colours and the colours on the Fisher Price alphabet magnets she’d had as a kid. Could this be a direct example of sensory imprinting in early childhoodd which would confirm synesthetic associations as something more than random misfirings?

Dr David Eagleman, director of the Laboratory for Perception and Action at the Baylor College of Medicine, decided to try and find out. He collected data from 6588 synesthetes and came up with some conclusive results: six percent of the synesthetes had 10 or more letters which matched the magnet set, a statistic greatly surpassing chance. Testing the hypothesis further, the lab found no one born before 1967 seemed to have imprinted on the toy, but a striking 15 percent of those born between 1975 and 1980 did have colours that matched the set, marking a direct correspondence with the heyday of Fisher Price letter-fridge-magnet marketing. After 1990, when the magnet set went out of production, the percentage of magnet imprinting showed a decline.

Still more fodder for the “ideasthesia” concept can be found in what’s known as ordinal-linguistic-personification, or “OLP synesthesia,” in which ordered sequences like numbers or the alphabet are associated with personalities and genders. OLP synesthetes, for example, might perceive the letter B as a kindly woman in an apron or number 4 as a skater-punk in shades and a baseball cap. Pythagoras himself suggested genders for numbers though his pronouncement that even numbers were female and odd numbers were male was probably more theoretical than synesthetic. Some synesthetes position sequences like numbers or the calendar year in specific locations in space, yet another example of a conceptual fusion.

Colour dementia bright

Linking words to colours could prove useful for the 96 percent of the population without synesthesia. Dr Clare Jonas at the University of East London is currently training non-synesthetes to associate certain letters with certain colours to find out if people can remember coloured words that match their training more easily. So far the results look good. The hope is that synesthesia training could help patients recover from brain injuries or ward off cognitive decline in old age by enhancing visual mental imagery and memory performance.

Co-editor of The Oxford Handbook of Synesthesia, Dr Julia Simner, was recently awarded a grant to develop the fist test to identify synesthesia in children. Synesthetes learn differently than other children, say some researchers, and would benefit from being acknowledged for their unique qualities. So while synesthetes of yore were mocked for their fanciful colour-rich pronouncements, the coming generations of word-tasters and colour-seers may enjoy special attention of a brighter, more magenta, more honey-tasting sort.

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