After the second stroke, doctors did tests to see whether it had rendered TN completely blind, for some of the blind have a small measure of residual sight. They can see light and dark, for example, or read a word if it covers the side of a barn. TN, though, could not even see the barn. The doctors who examined him after his second stroke noted that he could not discern shapes or detect movement or colors, or even the presence of an intense source of light. An exam confirmed that the visual areas in his occipital lobe were not functioning. Though the optical part of TN’s visual system was still fully functional, meaning his eyes could gather and record light, his visual cortex lacked the ability to process the information that his retinas were sending it. Because of this state of affairs—an intact optical system, but a completely destroyed visual cortex—TN became a tempting subject for scientific research, and, sure enough, while he was still in the hospital a group of doctors and researchers recruited him.
There are many experiments one can imagine performing on a blind subject like TN. One could test for an enhanced sense of hearing, for example, or memory for past visual experiences. But of all possible questions, one that would probably not make your list would be whether a blind man can sense your mood by staring at your face. Yet that is what these researchers chose to study.12
They began by placing a laptop computer a couple feet in front of TN and showing him a series of black shapes—either circles or squares—presented on a white background. Then, in the tradition of Charles Sanders Peirce, they presented him with a forced choice: when each shape appeared, they asked him to identify it. Just take a stab at it, the researchers pleaded. TN obliged. He was correct about half the time, just what one would expect if he truly had no idea what he was seeing. Now comes the interesting part. The scientists displayed a new series of images—this time, a series of angry and happy faces. The game was essentially the same: to guess, when prompted, whether the face on the screen was angry or happy. But identifying a facial expression is a far different task from perceiving a geometric shape, because faces are much more important to us than black shapes.
Faces play a special role in human behavior.13 That’s why, despite men’s usual preoccupation, Helen of Troy was said to have “the face that launched a thousand ships,” not “the breasts that launched a thousand ships.” And it’s why, when you tell your dinner guests that the tasty dish they are savoring is cow pancreas, you pay attention to their faces and not their elbows—or their words—to get a quick and accurate report of their attitudes toward organ meat. We look to faces to quickly judge whether someone is happy or sad, content or dissatisfied, friendly or dangerous. And our honest reactions to events are reflected in facial expressions controlled in large part by our unconscious minds. Expressions, as we’ll see in Chapter 5, are a key way we communicate and are difficult to suppress or fake, which is why great actors are hard to find. The importance of faces is reflected in the fact that, no matter how strongly men are drawn to the female form, or women to a man’s physique, we know of no part of the human brain dedicated to analyzing the nuances of bulging biceps or the curves of firm buttocks or breasts. But there is a discrete part of the brain that is used to analyze faces. It is called the fusiform face area. To illustrate the brain’s special treatment of faces, look at the photos of President Barack Obama here.14
The photo on the left of the right-side-up pair looks horribly distorted, while the left member of the upside-down pair does not look very unusual. In reality the bottom pair is identical to the top pair, except that the top photos have been flipped. I know because I flipped them, but if you don’t trust me just rotate this book 180 degrees, and you’ll see that what is now the top pair will appear to have the bad photo, and what is now the bottom pair will look pretty good. Your brain devotes a lot more attention (and neural real estate) to faces than to many other kinds of visual phenomena because faces are more important—but not upside-down faces, since we rarely encounter those, except when performing headstands in a yoga class. That’s why we are far better at detecting the distortion on the face that is right side up than on the one that is flipped over.
The researchers studying TN chose faces as their second series of images in the belief that the brain’s special and largely unconscious focus on faces might allow TN to improve his performance, even though he’d have no conscious awareness of seeing anything. Whether he was looking at faces, geometric shapes, or ripe peaches ought to have been a moot point, given that TN was, after all, blind. But on this test TN identified the faces as happy or angry correctly almost two times out of three. Though the part of his brain responsible for the conscious sensation of vision had obviously been destroyed, his fusiform face area was receiving the images. It was influencing the conscious choices he made in the forced-choice experiment, but TN didn’t know it.
Having heard about the first experiment involving TN, a few months later another group of researchers asked him if he would participate in a different test. Reading faces may be a special human talent, but not falling on your face is even more special. If you suddenly notice that you are about to trip over a sleeping cat, you don’t consciously ponder strategies for stepping out of the way; you just do it.15 That avoidance is governed by your unconscious, and it is the skill the researchers wanted to test in TN. They proposed to watch as he walked, without his cane, down a cluttered hallway.16
The idea excited all those involved except the person not guaranteed to remain vertical. TN refused to participate.17 He may have had some success in the face test, but what blind man would consent to navigating an obstacle course? The researchers implored him, in effect, to just do it. And they kindly offered to have an escort trail him to make sure he didn’t fall. After some prodding, he changed his mind. Then, to the amazement of everyone, including himself, he zigged and zagged his way perfectly down the corridor, sidestepping a garbage can, a stack of paper, and several boxes. He didn’t stumble once, or even collide with any objects. When asked how he’d accomplished this, TN had no explanation and, one presumes, requested the return of his cane.
The phenomenon exhibited by TN—in which individuals with intact eyes have no conscious sensation of seeing but can nevertheless respond in some way to what their eyes register—is called “blindsight.” This important discovery “elicited disbelief and howls of derision” when first reported and has only recently come to be accepted.18 But in a sense it shouldn’t have been surprising: it makes perfect sense that blindsight would result when the conscious visual system is rendered nonfunctional but a person’s eyes and unconscious system remain intact. Blindsight is a strange syndrome—a particularly dramatic illustration of the two tiers of the brain operating independently of each other.
THE FIRST PHYSICAL indication that vision occurs through multiple pathways came from a British Army doctor named George Riddoch in 1917.19 In the late nineteenth century, scientists had begun to study the importance of the occipital lobe in vision by creating lesions in dogs and monkeys. But data on humans was scarce. Then came World War I. Suddenly the Germans were turning British soldiers into promising research subjects at an alarming pace. This was partly because British helmets tended to dance atop the soldiers’ heads, which might have looked fashionable but didn’t cover them very well, especially in the back. Also, the standard in that conflict was trench warfare. As it was practiced, a soldier’s job was to keep all of his body protected by the solid earth except for his head, which he was instructed to stick up into the line of fire. As a result, 25 percent of all penetrating wounds suffered by British soldiers were head wounds, especially of the lower occipital lobe and its neighbor the cerebellum.