In the mornings, my cat often takes up a post on my chest. His presence is heralded by a chirpy meow and four quarter-sized points of pressure where his feet make contact; as he relaxes, he settles into a loud, rhythmic purr, and the pressure of his 16 pounds is more evenly distributed across my ventral torso. If I'm slow to open my eyes, he reaches out a paw and gently pricks my face with his claws ‹ enough to make an impression but not do real damage. When I do open my eyes, I see the triangles of his ears, the dense, velvety blackness of his fur and the sheen of his nose; his yellow irises are thin rings around his dilated pupils in the dim, early light.
Suppose I ...view middle of the document...
Synesthetic perceptions are involuntary and are reliably triggered by the phenomena that induce them. They are also consistent over time for a given synesthete; that is, a true synesthete for whom the musical note E produces a percept of red triangles on a field of yellow will invariably experience that sound that way. (2)
There is, however, no consistency of synesthetic perceptions from one synesthete to another: while a high percentage of them experience colored letters, for instance, they do not agree with one another on what color each letter evokes. Synesthetic sensations do not replace, but add to, the perceptions of the triggering stimuli in more usual modes. In almost all cases, synesthetic correspondences are a one-way street: if sounds induce the perception of colors, for instance, colors do not induce the perception of sounds. Synesthesia appears to be a heritable trait and is more common in women than in men. (3)
Interest in synesthesia, from the Greek syn (with or together) and aisthesis (perception or sense-impression) has mushroomed in the past decade or so. Accounts in the popular news media have prompted more and more reports of the condition, and estimates of the frequency of its occurrence have risen correspondingly. In 1995, a CNN interview with Richard Cytowic, a medical doctor and synesthesia researcher who wrote the popular 1993 book The Man Who Tasted Shapes, used Cytowic's figure of 1 case of synesthesia for every 25,000 people. (4) By March 2001, a story in the San Francisco Chronicle asserted that " As many as one in a few hundred humans may be synesthetes." (5) Another recent estimate, based on the number of people who responded to a British researcher's advertisement for synesthetes relative to the circulation of the newspaper in which he advertised, is 1 in 2,000. (6)
Why the sudden interest? According to Cytowic, the phenomenon has been recognized by medicine for at least 300 years, but studying it has gone in and out of fashion. There was a wave of interest about a century ago, but after interest peaked and the phenomenon remained unexplained, synesthesia lost its appeal to researchers, a situation Cytowic attributes to the dominance of behaviorist theory that deemed the study of subjective, undocumentable experiences like synesthesia unfit objects for scientific study. (2)
Indeed, the sudden popularity of synesthesia research can be explained in part by the development of sophisticated brain-imaging techniques that give observers concrete evidence that synesthetes' brains operate differently from nonsynesthetes'. (7) Now researchers are eager to investigate the neural circuitry that results in synesthesia, and many hope that the brain functions of synesthetics can provide insight into the way sense perception is normally integrated and even the physical processes that underlie consciousness. Since the latest phase of synesthesia research began, however, there has been little...