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

“That’s a tough one. It’s something I have often asked myself. I guess I do really see it. That number you drew looks distinctly red to me. But I can also see that it’s really black—or I should say, I know it’s black. So in some sense it is a memory image of sorts…I must be seeing it in my mind’s eye or something. But it certainly doesn’t feel like that. It feels like I am actually seeing it. It’s very hard to describe, Doctor.”

“You are doing very well, Susan. You are a good observer and that makes everything you say valuable.”

“Well, one thing I can tell you for sure is that it isn’t like imagining a pumpkin when looking at a picture of Cinderella or listening to the word ‘Cinderella.’ I do actually see the color.”

One of the first things we teach medical students is to listen to the patient by taking a careful history. Ninety percent of the time you can arrive at an uncannily accurate diagnosis by paying close attention, using physical examination and sophisticated lab tests to confirm your hunch (and to increase the bill to the insurance company). I started to wonder whether this dictum might be true not just for patients but for synesthetes as well.

I decided to give Susan some simple tests and questions. For example, was it the actual visual appearance of the numeral that evoked the color? Or was it the numerical concept—the idea of sequence, or even of quantity? If the latter, then would Roman numerals do the trick or only Arabic ones? (I should call them Indian numerals really; they were invented in India in the first millennium B.C.E. and exported to Europe via Arabs.)

I drew a big VII on the pad and showed it to her.

“What do you see?”

“I see it’s a seven, but it looks black—no trace of red. I have always known that. Roman numerals don’t work. Hey, Doctor, doesn’t that prove it can’t be a memory thing? Because I do know it’s a seven but it still doesn’t generate the red!”

Ed and I realized that we were dealing with a very bright student. It was starting to look like synesthesia was indeed a genuine sensory phenomenon, brought on by the actual visual appearance of the numeral—not by the numerical concept. But this was still well short of proof. Could we be absolutely sure that this wasn’t happening because early in kindergarten she had repeatedly seen a red seven on her refrigerator door? I wondered what would happen if I showed her black-and-white halftone photos of fruits and vegetables which (for most of us) have strong memory-color associations. I drew pictures of a carrot, a tomato, a pumpkin, and a banana, and showed them to her.

“What do you see?”

“Well, I don’t see any colors, if that’s what you’re asking. I know the carrot is orange and can imagine it to be so, or visualize it to be orange. But I don’t actually see the orange color the way I see red when you show me the 7. It’s hard to explain, Doctor, but it’s like this: When I see the black-and-white carrot, I kinda know it’s orange, but I can visualize it as being any bizarre color I want, like a blue carrot. It’s very hard for me to do that with 7; it keeps screaming red at me! Is all of this making any sense to you guys?”

“Okay,” I told her, “now I want you to close your eyes and show me your hands.”

She seemed slightly startled by my request but followed my instructions. I then drew the numeral 7 on the palm of her hand.

“What did I draw? Here, let me do it again.”

“It’s a 7!”

“Is it colored?”

“No, absolutely not. Well, let me rephrase that; I don’t initially see red even though I ‘feel’ it’s 7. But then I start visualizing the 7, and it’s sort of tinged red.”

“Okay, Susan, what if I say ‘seven’? Here, let’s try it: Seven, seven, seven.”

“It wasn’t red initially, but then I started to experience red…Once I start visualizing the appearance of the shape of 7, then I see the red—but not before that.”

On a whim I said, “Seven, five, three, two, eight. What did you see then, Susan?”

“My God…that’s very interesting. I see a rainbow!”

“What do you mean?”

“Well, I see the corresponding colors spread out in front of me as in a rainbow, with the colors matching the number sequence you read aloud. It’s a very pretty rainbow.”

“One more question, Susan. Here is that drawing of 7 again. Do you see the color directly on the number, or does it spread around it?”

“I see it directly on the number.”

“What about a white number on black paper? Here is one. What do you see?”

“It’s even more clearly red than the black one. Dunno why.”

“What about double-digit numbers?” I drew a bold 75 on the pad and showed it to her. Would her brain start blending the colors? Or see a totally new color?

“I see each number with its appropriate color. But I have often noticed this myself. Unless the numbers are too close.”

“Okay, let’s try that. Here, the 7 and 5 are much closer together. What do you see?”

“I still see them in the correct colors, but they seem to ‘fight’ or cancel each other; they seem dimmer.”

“And what if I draw the number seven in the wrong-color ink?”