The Tell-Tale Brain

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.

Francesca came into the lab one day, having seen an ad in the San Diego Reader. After tea and the usual pleasantries my student David Brang and I hooked her up to our ohmmeter to measure her GSR. As we saw in the Chapter 2, this device measures the moment-to-moment microsweating produced by fluctuating levels of emotional arousal. Unlike a person, who can verbally dissemble or even be subconsciously deluded about how something makes her feel, GSR is instantaneous and automatic. When we measured GSR in normal subjects who touched various mundane textures such as corduroy or linoleum, it was clear they experienced no emotions. But Francesca was different. For the textures that she reported gave her strong emotional reactions, such as fear or anxiety or disgust, her body produced a strong GSR signal. But when she touched textures that she said gave her warm, relaxed feelings, there was no change in the electrical resistance of her skin. Since you cannot fake GSR responses, this provided strong evidence that Francesca was telling us the truth.

But to be absolutely sure that Francesca was experiencing specific emotions, we used an added procedure. Again we took her into a room and hooked her up to the ohmmeter. We asked her to follow instructions on a computer screen that would tell her which of several objects that were laid out on the table in front of her she was to touch and for how long. We said she would be alone in the room since noises from our presence might interfere with the GSR monitoring. Unbeknownst to her, we had a hidden video camera behind the monitor to record all her facial expressions. The reason we did this secretively was to ensure that her expressions were genuine and spontaneous. After the experiment, we had independent student evaluators rate the magnitude and quality of the expressions on her face, such as fear or calm. Of course we made sure that the evaluators didn’t know the purpose of the experiment and didn’t know what object Francesca had been touching on any given trial. Once again we found that there was clear correlation between Francesca’s subjective ratings of various textures and her spontaneous facial expressions. It seemed quite clear, therefore, that the emotions she claimed to experience were authentic.

MIRABELLE, AN EBULLIENT, dark-haired young lady, had been eavesdropping on a conversation I had been having with Ed Hubbard at the Espresso Roma Cafe on campus, a stone’s throw away from my office. She arched her eyebrows—whether from amusement or skepticism, I couldn’t tell.

She came to our lab shortly thereafter to volunteer as a subject. Like Susan and Becky, every number appeared to Mirabelle to be tinged with a particular color. Susan and Becky had convinced us informally that they were reporting their experience accurately and truthfully, but with Mirabelle we wanted to see if we could scare up some hard proof that she was really seeing color (as when you see an apple) rather than just experiencing a vague mental picture of color (as when you imagine an apple). This boundary between seeing and imagining has always proved elusive in neurology. Perhaps synesthesia would help resolve the distinction between them.

I waved her toward a chair in my office, but she was reluctant to sit. Her eyes darted all around the room looking at the various antique scientific instruments and fossils lying on the table and on the floor. She was like the proverbial kid in a candy store as she crawled all around the floor looking at a collection of fossil fishes from Brazil. Her jeans were sliding down her hips, and I tried not to gaze directly at the tattoo on her waist. Mirabelle’s eyes lit up when she saw a long, polished fossilized bone which looked a bit like a humerus (upper arm bone). I asked her to guess what it was. She tried rib, shin bone, and thigh bone. In fact, it was the baculum (penis bone) of an extinct Pleistocene walrus. This particular one had obviously been fractured in the middle and had rehealed at an angle while the animal was alive, as evidenced by a callus formation. There was also a healed, callused tooth mark on the fracture line, suggesting the fracture had been caused by a sexual or predatory bite. There is a detective aspect to paleontology just as there is in neurology, and we could have gone on with all this for another two hours. But we were running out of time. We needed to get back to her synesthesia.

We began with a simple experiment. We showed Mirabelle a white number 5 on a black computer screen. As expected, she saw it in color—in her case, bright red. We had her fix her gaze on a small white dot in the middle of the screen. (This is called a fixation spot; it keeps the eyes from wandering). We then gradually moved the number farther and farther away from the central spot to see if this did anything to the color that was evoked. Mirabelle pointed out that the red color became progressively less vivid as the number was moved away, eventually becoming a pale desaturated pink. This in itself may not seem very surprising; a number seen off- axis prompts a weaker color. But it was nonetheless telling us something important. Even seen off to the side the number itself was still perfectly identifiable, yet the color was much weaker. In one stroke this result showed that synesthesia can’t be just a childhood memory or a metaphorical association.¹ If the number were merely evoking the memory or the idea of a color, why should it matter where it was placed in the visual field, so