Smilack says her synesthesia helps her create art, such as this piece, "Squid Row." Photo by Marcia Smilack.
By early October, the summer tourists have left Martha's Vineyard. Marcia Smilack, camera in hand, walks slowly along a barren dock, waiting for something in her peripheral vision to evoke the sound of a cello in her ears or the feel of satin on her skin. When it does, she stops, points her camera at the water, and waits to hear or feel it again. Then she shoots her picture.
Smilack belongs to the group of one to four percent of people worldwide with synesthesia, the neurological mixing of the senses. No two synesthetes have exactly the same perceptual experiences. Many perceive each number, letter of the alphabet, or day of the week as a different color. For others, sounds from the environment are always accompanied by moving geometric patterns in their "mind's eye."
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Smilack has a rare form of synesthesia that involves all of her senses—the sound of one female voice looks like a thin, bending sheet of metal, and the sight of a certain fishing shack gives her a brief taste of Neapolitan ice cream—but her artistic leanings are shared by many other synesthetes. Scientists estimate that synesthesia is about seven times more common in poets, novelists, and artists than in the rest of the population. (Some of the most famous examples include artists David Hockney and Wassily Kandinsky and writer Vladimir Nabokov.)
In the last decade, this connection between synesthesia and art has drawn much attention from neuroscientists. And now several genetic and behavioral studies aim to pin down the biological mechanisms linking art and synesthesia, with hopes of answering even bigger questions about how every brain perceives art.
"Until seven or eight years ago, it was still a long-standing question whether the things these people were saying, this synesthesia, was real or bogus," said Vilayanur Ramachandran, a neuroscientist at the University of California, San Diego.
But in 1999, Ramachandran and his colleagues began giving tests to synesthetes that showed they weren't making up their sensory experiences. In one test, a computer showed the image of a square with a few black '2's scattered within a block of black '5's. Researchers then asked the subjects what shape the '2's made. For most people, Ramachandran said, this task may be impossible, and those who can complete it take several minutes. But for synesthetes who see a '2' as a different color from a '5,' it was simple: 90 percent identified the correct shape, and most did it in just a few seconds.
Subsequent experiments by Ramachandran and others using brain scanners also confirmed that synesthesia is a genuine sensory experience.
Ramachandran says that since the areas of the brain that are activated by color are adjacent to those activated by number, synesthesia might be a result of some kind of "cross wiring" in the brain.
"When we're born, the brain has all kinds of connections, and these gradually get pruned," Ramachandran said. "So synesthesia might be a mutation of this pruning gene, or set of genes, so that adjacent areas don't get separated."
Since synesthesia runs in families, most scientists agree it must have a strong genetic component. For the last two years, neuroscientist David Eagleman of the Baylor College of Medicine has been collecting DNA from large families of synesthetes and analyzing it for "hot spots"—groups of about 100 genes that are distinct from non-synesthetes.
Eagleman's first round of analysis, which he intends to publish in the next couple of months, includes samples from about 150 synesthetes and identifies one promising hot spot on chromosome 16.
Now that he's identified a hot spot, Eagleman says the next step is to sequence that particular region in both synesthetes and non-synesthetes to find one or more "synesthetic" genes.