Do the letters of the alphabet each “taste” different to you—for instance, an “A” is chocolate, while a “Q” tastes like anchovies? When you have a headache, do you feel purple? When you listen to someone speaking, do their words have different shapes? Unless you’ve unknowingly ingested a hallucinogen like LSD or mushrooms, it’s likely that you have synesthesia, a blending of the senses characterized by stimulation of one sense (say, sight) activating or inducing sensation in another (hearing, for example). Synesthetes may feel sounds, hear colors, or taste shapes.
Though synesthesia is considered rare, there are no hard statistics on the incidence of it, with estimates ranging from as few as 1 in 100,000 people to as many as 1 in 200. According to Ronald I. Jacobson, MD, chief of Pediatric Neurology at Boston Children’s Health Physicians (formerly CWPW) and Maria Fareri Children’s Hospital, synesthesia “doesn’t represent a disorder or disease,” he says. “It’s a phenomenon, usually a normal phenomenon, just a variation of normal. It occurs in healthy people, and many people who have it don’t even know what it’s called.” In fact, contrary to what one may assume, according to Jacobson, synesthesia differs from hallucinations and is not psychiatric or psychological.
“Synesthesia is an elemental story,” he says. “It is one thing standing in for something else. A psychiatric disturbance is more complicated; it has more content.” Unlike drug-induced hallucinations, synesthetic sensations are very consistent: A letter is always the same color; a food is always the same shape. Jacobson knows a lot about synesthesia: As a child, he experienced it. “Whenever I had a toothache, I felt ‘yellow,’” he recalls. His synesthesia disappeared by the time he was an adult.
There are different types of synesthetic perceptions, including sensory (in which senses elicit the perception); cognitive (concepts such as numbers or letters induce it); and emotional (feelings such as love or sadness induce it). The phenomenon, says Jacobson, rarely interferes with day-to-day lives of those who experience it.