Carol Crane loves most kinds of music, but concerts affect her in a peculiar way. "The sound of guitars always feels like someone is blowing on my ankles. The piano presses on me right here," she says, tapping her chest just over her heart. "And New Orleans-type jazz hits me all over like heavy, sharp raindrops."
Crane's sensory reaction to letters and numbers is just as odd. At the sight of the letter a, a color flashes through her mind—invariably gray-blue. The letter b, she says, is navy blue, and c tawny crimson. Numbers trigger similar sensations. The numeral 4 causes Crane to see tomato red and, like all of her perceptual links, it has done so since childhood. Four has always been red, she says. It can't be anything else.
Crane, a 47-year-old psychologist, is not delusional. Her perceptions, bizarre as they might seem, stem from an unusual intermingling of the senses known as synesthesia, a condition that can take a multitude of forms. Some synesthetes see sounds, while others feel colors or taste shapes. Simon Baron-Cohen, an experimental psychologist at the University of Cambridge, estimates that perhaps one in 2,000 people is synesthetic and goes through life with at least one sense jostling another. Little is known about what causes the condition, but one thing is certain: The sensations a synesthete experiences are quite real. As Baron-Cohen puts it, "We've ruled out that these people are simply telling tall tales."
Synesthesia—from the Greek syn, for together, and aisthesis, to perceive—generated a wave of scientific and popular interest around the turn of the twentieth century. Russian composer Alexander Scriabin, himself a synesthete, featured an organ that produced multihued light beams in his symphony Prometheus, the Poem of Fire. To many fin de siècle Romantics, synesthetes appeared to be humanity's spiritual vanguard, closer to God than the sense-segregated masses. "Such highly sensitive people," wrote Wassily Kandinsky, the Russian abstract artist, "are like good, much-played violins, which vibrate in all their parts and fibers at every touch of the bow." The fascination soon peaked, however, stymied by synesthesia's sheer impenetrability. The problem: No one could crawl into synesthetes' heads to understand or share their unique perceptions.
That may soon change. Propelled by recent advances in brain imaging and electrophysiological recording, as well as DNA analysis and other techniques, a small but determined cadre of researchers in the United States, Scotland, England, Canada, Australia, France, Germany, Israel, and Finland is beginning to sort out just what, exactly, distinguishes synesthetes from the rest of us. The answers promise to do more than just shed light on a quirky condition—they may illuminate a central existential conundrum. While the notion that synesthetes are semidivine no longer holds sway, cognitive scientists contend that these unusual people are precious windows into the ultimate mystery of human consciousness.
