Tasting words, smelling shapes and other synesthetic experiences can have their advantages. The condition has long been linked to creativity—as the lists of famous artists, writers and musicians with synesthesia would suggest—and the strange sensory overlaps may also boost memory. All of which leads many nonsynesthetes to wonder whether they could learn to see sound and taste letters.
There are several “artificial” approaches to synesthesia—sensory deprivation or psychedelic drugs, for instance, are purported to achieve a similar effect—but in most “natural” cases there is clearly a genetic component. Still, learned experience plays an important role in establishing specific sensory associations. This fact can help explain why, for example, people who see letters in color often see A, a frequently used letter, in red, a common hue.
Some experiments suggest people can be trained to acquire synesthetic experiences. In 2014 psychologist Nicolas Rothen and his colleagues, all then at the University of Sussex in England, signed up 14 volunteers—who had no personal history of synesthesia—for an intensive training course in which they were taught 13 letter-color associations. After nine weeks the participants started seeing letters in color even outside the laboratory. But the results of other similar studies were mixed, with several failing to train people to experience any form of synesthesia.
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In one case report, a nonsynesthete spent eight years mastering the art of cross-stitching, in which numbers signify the use of specific thread colors (for example, “3” means “red”). When the nonsynesthete's performance on connecting colors with numbers was compared with that of a synesthete, the two were basically indistinguishable. But there was a catch. During functional MRI tests, their brains lit up very differently, suggesting that the experience of the synesthete was unlike that of the trained person. What is unique to synesthesia, the authors conclude, are “photisms”—involuntary, hallucinationlike sensations of light or color.
In 2014 Rothen and psychologist Beat Meier of the University of Bern in Switzerland reviewed the seven synesthesia-training studies published to date. They concluded that even if we can train some aspects of synesthesia so some people can mimic these sensations, the true experience probably remains out of reach for most of us.