The Tell-Tale Brain: A Neuroscientist's Quest for What Makes Us Human

I drew a green 7 on the pad and showed it to her.

“Ugh! It looks hideous. It jars, like there is something wrong with it. I certainly don’t mix the real color with the mental color. I see both colors simultaneously, but it looks hideous.”

Susan’s remark reminded me of what I had read in the older papers on synesthesia, that the experience of color was often emotionally tinged for them and that incorrect colors could produce a strong aversion. Of course, we all experience emotions with certain colors. Blue seems calming, and red is passionate. Could it be that the same process is, for some odd reason, exaggerated in synesthetes? What can synesthesia tell us about the link between color and emotion that artists like Van Gogh and Monet have long been fascinated by?

There was a hesitant knock on the door. We hadn’t noticed that almost an hour had passed and that the other student, a girl named Becky, was still outside my office. Fortunately, she was cheerful despite having waited so long. We asked Susan to come back the following week and invited Becky in. It turned out that she too was a synesthete. We repeated the same questions and conducted the same tests on her as we had on Susan. Her answers were uncannily similar with a few minor differences.

Becky saw colored numbers, but hers were not the same as Susan’s. For Becky, 7 was blue and 5 was green. Unlike Susan, she saw letters of the alphabet in vivid colors. Roman numerals and numbers drawn on her hand were ineffective, which suggested that, as in Susan, the colors were driven by the visual appearance of the number and not by the numerical concept. And lastly, she saw the same rainbow-like effect that Susan saw when we recited a string of random numbers.

I realized then and there that we were hot on the trail of a genuine phenomenon. All my doubts were dispelled. Susan and Becky had never met each other before, and the high level of similarity between their reports couldn’t possibly be a coincidence. (We later learned that there’s a lot of variation among synesthetes, so we were very lucky to have stumbled on two very similar cases.) But even though I was convinced, we still had a lot of work to do to produce evidence strong enough to publish. People’s verbal commentaries and introspective reports are notoriously unreliable. Subjects in a laboratory setting are often highly suggestible and may unconsciously pick up what you want to hear and oblige by telling you that. Furthermore, they sometimes speak ambiguously or vaguely. What was I to make of Susan’s perplexing remark? “I really do see red, but I also know it’s not—so I guess I must be seeing it in my mind’s eye or something.”

SENSATION IS INHERENTLY subjective and ineffable: You know what it “feels” like to experience the vibrant redness of a ladybug’s shell, for instance, but you could never describe that redness to a blind person, or even to a color-blind person who cannot distinguish red from green. And for that matter, you can never truly know whether other people’s inner mental experience of redness is the same as yours. This makes it somewhat tricky (to put it mildly) to study the perception of other people. Science traffics in objective evidence, so any “observations” we make about people’s subjective sensory experience are necessarily indirect or secondhand. I would point out though that subjective impressions and single-subject case studies can often provide strong clues toward designing more formal experiments. Indeed, most of the great discoveries in neurology were initially based on simple clinical testing of single cases (and their subjective reports) before being confirmed in other patients.

One of the first “patients” with whom we launched a systematic study in search of hard proof of the reality of synesthesia was Francesca, a mild-mannered woman in her midforties who had been seeing a psychiatrist because she had been experiencing a mild low-grade depression. He prescribed lorazepam and Prozac, but not knowing what to make of her synesthetic experiences, referred her to my lab. She was the same woman I mentioned earlier who claimed that right from very early childhood she experienced vivid emotions when she touched different textures. But how could we test the truth of her claim? Perhaps she was just a highly emotional person and simply enjoyed speaking about the emotions that various objects triggered in her. Perhaps she was “mentally disturbed” and just wanted attention or to feel special.