You’ve probably heard Mondays referred to as “blue,” or a brightly colored shirt as “loud.” For most people, these descriptions are figurative. Mondays don’t really conjure a turquoise haze, and shirts don’t emit high-pitched screeches. But for some people, called synesthetes, such cross-sensory experiences are quite literal.
When Carol Steen, now in her sixties, was a girl growing up in Detroit, she used to walk home from elementary school with a friend. One day, perhaps after a lesson in spelling or an exercise in handwriting, seven-year-old Steen asked her classmate, “Isn’t the letter ‘A’ the prettiest pink?” Her classmate, in the way only kids can, wrinkled her nose and pronounced Steen “weird.”
That was the first time Steen realized that not everyone saw beautiful, intense colors in letters and numbers like she did. It was also the last time she talked about it, until thirteen years later at the family dinner table. “The number five is yellow,” Steen commented. Her mother and brother looked at her blankly, but her father disagreed. “No,” he said. “It’s yellow-ochre.”
What Is It?
Synesthesia, from the Greek syn for “together” and aisthēsis for “sensation,” is a neurological condition (Steen would say “ability”) in which one sensory experience automatically and consistently triggers another sensory or cognitive perception. A synesthete might literally see sound or taste color.
Today, synesthesia is believed to be far more common than once thought, occurring in as many as one in twenty-three people. There are more than sixty documented forms of synesthesia, covering all five senses, but some are more frequent than others:
Grapheme-color synesthesia: With the most common form of synesthesia, grapheme-color synesthetes perceive very definite colors in units of written language, like numbers or letters, called “graphemes.” For example, “A” is scarlet-red, or “7” is lime-green.
Number-form synesthesia: Numbers, months, years, days, or dates—anything with a serial order—are attributed with a place in space. For example, the months of the year might be seen as situated like the numbers on the face of a clock, or 2008 might appear further away or higher or lower than 2003.
Sound-color synesthesia: Sounds elicit colors. For example, E flat played on a piano might trigger a lavender aura, while F sharp triggers sky-blue. Or a sonata appears as streaks of azure, while the sound of a dog barking is perceived in waves of crimson.
Ordinal-linguistic personification: Ordered sequences like numbers, dates, or months have personality traits. For example, “1” might be angry and bitter; “May” is humorous and well-liked.
What Causes Synesthesia?
In Europe in the 1880s, there was a burst of interest in synesthesia, an interest so keen that some intellectuals and artists of the era are even thought to have faked it. Science lost interest by the middle of the next century, and only in the past few decades have neurologists turned their attention again to the condition and unlocked some of the mysteries surrounding how synesthesia actually works.
Using advancements in medical technology, particularly functional neuroimaging with PET scans and fMRIs, researchers have been able to identify which parts of the brain and which neural pathways are firing during a synesthetic experience. In the brain of a synesthete, researchers see “cross-talk” between parts of the brain associated with different senses. A popular theory holds that we are all born with our senses, in effect, wired together. As most babies grow, those sensory connections either become unplugged and the neural pathways “pruned,” or the cross-talk becomes inhibited. In synesthetes, this never happens.
The fact that synesthesia often runs in families suggests a genetic link. But some people experience synesthesia during or after an acute experience like a stroke, an epileptic seizure, or the use of psychedelic drugs. An important point, however, is that while the individual experiences of synesthetes are consistent, often very intense, and even pleasurable—Steen describes hers like the aurora borealis with the brilliance of gemstones under halogen lights—experiences between synesthetes of the same form can vary widely. As Steen jokes, “If you put two synesthetes in the same room together, they’ll bond in the most curious way. ‘What color is your A?’ one will ask, and be horrified by the incorrect answer.”
