Francis Galton, a cousin of Charles Darwin and one of the most colorful and eccentric scientists of the Victorian era, conducted the first systematic study of synesthesia in the 1890s. Galton made many valuable contributions to psychology, especially the measurement of intelligence. Unfortunately, he was also an extreme racist; he helped usher in the pseudoscience of eugenics, whose goal was to “improve” mankind by selective breeding of the kind practiced with domesticated livestock. Galton was convinced that the poor were poor because of inferior genes, and that they must be forbidden from breeding too much, lest they overwhelm and contaminate the gene pool of the landed gentry and rich folk like him. It isn’t clear why an otherwise intelligent man should hold such views, but my hunch is that he had an unconscious need to attribute his own fame and success to innate genius rather than acknowledging the role of opportunity and circumstance. (Ironically, he himself was childless.)
Galton’s ideas about eugenics seem almost comical in hindsight, yet there is no denying his genius. In 1892 Galton published a short article on synesthesia in the journal Nature. This was one of his lesser-known papers, but about a century later it piqued my interest. Although Galton wasn’t the first to notice the phenomenon, he was the first to document it systematically and encourage people to explore it further. His paper focused on the two most common types of synesthesia: the kind in which sounds evoke colors (auditory-visual synesthesia) and the kind in which printed numbers always seem tinged with inherent color (grapheme-color synesthesia). He pointed out that even though a specific number always produces the same color for any given synesthete, the number-color associations are different for different synesthetes. In other words, it’s not as though all synesthetes see a 5 as red or a 6 as green. To Mary, 5 always looks blue, 6 is magenta, and 7 is chartreuse. To Susan, 5 is vermillion, 6 is light green, and 4 is yellow.
How to explain these people’s experiences? Are they crazy? Do they simply have vivid associations from childhood memories? Are they just speaking poetically? When scientists encounter anomalous oddities such as synesthetes, their initial reaction is usually to brush them under the carpet and ignore them. This attitude—which many of my colleagues are very vulnerable to—is not as silly as it seems. Because a majority of anomalies—spoon bending, alien abduction, Elvis sightings—turn out to be false alarms, it’s not a bad idea for a scientist to play it safe and ignore them. Whole careers, even lifetimes, have been wasted on the pursuit of oddities, such as polywater (a hypothetical form of water based on crackpot science), telepathy, or cold fusion. So I wasn’t surprised that even though we had known about synesthesia for over a century, it has generally been sidelined as a curiosity because it didn’t make “sense.”
Even now, the phenomenon is often dismissed as bogus. When I bring it up in casual conversation, I often hear it shot down on the spot. I’ve heard, “So you study acid junkies?” and “Whoa! Cuckoo!” and a dozen other dismissals. Unfortunately even physicians are not immune—and ignorance in a physician can be quite hazardous to people’s health. I know of at least one case in which a synesthete was misdiagnosed as having schizophrenia and was prescribed antipsychotic medication to rid her of hallucinations. Fortunately her parents took it upon themselves to get informed, and in the course of their reading came across an article on synesthesia. They drew this to the doctor’s attention, and their daughter was quickly taken off the drugs.
Synesthesia as a real phenomenon did have a few supporters, including the neurologist Dr. Richard Cytowic, who wrote two books about it: Synesthesia: A Union of the Senses (1989) and The Man Who Tasted Shapes (1993/2003). Cytowic was a pioneer, but he was a prophet preaching in the wilderness and was largely ignored by the establishment. It didn’t help matters that the theories he put forward to explain synesthesia were a bit vague. He suggested that the phenomenon was a kind of evolutionary throwback to a more primitive brain state in which the senses hadn’t quite separated and were being mingled in the emotional core of the brain.
This idea of an undifferentiated primitive brain didn’t make sense to me. If the synesthete’s brain was reverting to an earlier state, then how would you explain the distinctive and specific nature of the synesthete’s experiences? Why, for example, does Esmeralda “see” C-sharp as being invariably blue? If Cytowic was correct, you would expect the senses to just blend into each other to create a blurry mess.
A second explanation that is sometimes posed is that synesthetes are just remembering childhood memories and associations. Maybe they played with refrigerator magnets, and the 5 was red and the 6 was green. Maybe they remember this association vividly, just as you might recall the smell of a rose, the taste of Marmite or curry, or the trill of a robin in the spring. Of course, this theory doesn’t explain why only some people remain stuck with such vivid sensory memories. I certainly don’t see colors when looking at numbers or listening to tones, and I doubt whether you do either. While I might think of cold when I look at a picture of an ice cube, I certainly don’t feel it, no matter how many childhood experiences I may have had with ice and snow. I might say that I feel warm and fuzzy when stroking a cat, but I would never say touching metal makes me feel jealous.
A third hypothesis is that synesthetes are using vague tangential speech or metaphors when they speak of C-major being red or chicken tasting pointy, just as you and I speak of a “loud” shirt or “sharp” cheddar cheese. Cheese is, after all, soft to touch, so what do you mean when you say it is sharp? Sharp and dull are tactile adjectives, so why do you apply them without hesitation to the taste of cheese? Our ordinary language is replete with synesthetic metaphors—hot babe, flat taste, tastefully dressed—so maybe synesthetes are just especially gifted in this regard. But there is a serious problem with this explanation. We don’t have the foggiest idea of how metaphors work or how they are represented in the brain. The notion that synesthesia is just metaphor illustrates one of the classic pitfalls in science—trying to explain one mystery (synesthesia) in terms of another (metaphor).
What I propose, instead, is to turn the problem on its head and suggest the very opposite. I suggest that synesthesia is a concrete sensory process whose neural basis we can uncover, and that the explanation might in turn provide clues for solving the deeper question of how metaphors are represented in the brain and how we evolved the capacity to entertain them in the first place. This doesn’t imply that metaphor is just a form of synesthesia; only that understanding the neural basis of the latter can help illuminate the former. So when I resolved to do my own investigation of synesthesia, my first goal was to establish whether it was a genuine sensory experience.
IN 1997 A doctoral student in my lab, Ed Hubbard, and I set out to find some synesthetes to begin our investigations. But how? According to most published surveys, the incidence was anywhere from one in a thousand to one in ten thousand. That fall I was lecturing to an undergraduate class of three hundred students. Maybe we’d get lucky. So we made an announcement:
“Certain otherwise normal people claim they see sounds, or that certain numbers always evoke certain colors,” we told the class. “If any one of you experiences this, please raise your hands.”
To our disappointment, not a single hand went up. But later that day, as I was chatting with Ed in my office, two students knocked on the door. One of them, Susan, had striking blue eyes, streaks of red dye in her blonde ringlets, a silver ring in her belly button and an enormous skateboard. She said to us, “I’m one of those people you talked about in class, Dr. Ramachandran. I didn’t raise my hand because I didn’t want people to think I was weird or something. I didn’t even know that there were others like me or that the condition had a name.”