function. The other 95 percent goes on beyond our awareness and exerts a huge influence on our lives—beginning with making our lives possible.
One sign that there is a lot of activity going on in our brains of which we are not aware comes from a simple analysis of energy consumption.10 Imagine yourself sprawled on the couch watching television; you are subject to few demands on your body. Then imagine yourself doing something physically demanding—say, racing down a street. When you run fast, the energy consumption in your muscles is multiplied by a factor of one hundred compared to the energy you use as a couch potato. That’s because, despite what you might tell your significant other, your body is working a lot harder—one hundred times so—when you’re running than when you’re stretched out on the sofa. Let’s contrast this energy multiplier with the multiplier that is applicable when you compare two forms of mental activity: vegging out, in which your conscious mind is basically idle, and playing chess. Assuming that you are a good player with an excellent knowledge of all the possible moves and strategies and are concentrating deeply, does all that conscious thought tax your conscious mind to the same degree that running taxed your muscles? No. Not remotely. Deep concentration causes the energy consumption in your brain to go up by only about 1 percent. No matter what you are doing with your conscious mind, it is your unconscious that dominates your mental activity—and therefore uses up most of the energy consumed by the brain. Regardless of whether your conscious mind is idle or engaged, your unconscious mind is hard at work doing the mental equivalent of push-ups, squats, and wind sprints.
ONE OF THE most important functions of your unconscious is the processing of data delivered by your eyes. That’s because, whether hunting or gathering, an animal that sees better eats better and avoids danger more effectively, and hence lives longer. As a result, evolution has arranged it so that about a third of your brain is devoted to processing vision: to interpreting color, detecting edges and motion, perceiving depth and distance, deciding the identity of objects, recognizing faces, and many other tasks. Think of it—a third of your brain is busy doing all those things, yet you have little knowledge of or access to the processing. All that hard work proceeds outside your awareness, and then the result is offered to your conscious mind in a neat report, with the data digested and interpreted. As a result, you never have to bother figuring out what it means if these rods or those cones in your retinas absorb this or that number of photons, or to translate optic nerve data into a spatial distribution of light intensities and frequencies, and then into shapes, spatial positions, and meaning. Instead, while your unconscious mind is working feverishly to do all those things, you can relax in bed, recognizing, seemingly without effort, the lighting fixture on the ceiling—or the words in this book. Our visual system is not only one of the most important systems within our brain, it is also among the most studied areas in neuroscience. Understanding its workings can shed a lot of light on the way the two tiers of the human mind function together—and apart.
One of the most fascinating of the studies that neuroscientists have done on the visual system involved a fifty-two-year-old African man referred to in the literature as TN. A tall, strong-looking man, a doctor who, as fate would have it, was destined to become renowned as a patient, TN took the first step on his path to pain and fame one day in 2004 when, while living in Switzerland, he had a stroke that knocked out the left side of a part of his brain called the visual cortex.
The main part of the human brain is divided into two cerebral hemispheres, which are almost mirror images of each other. Each hemisphere is divided into four lobes, a division originally motivated by the bones of the skull that overlie them. The lobes, in turn, are covered by a convoluted outer layer about the thickness of a formal dinner napkin. In humans, this outer covering, the neocortex, forms the largest part of the brain. It consists of six thinner layers, five of which contain nerve cells, and the projections that connect the layers to one another. There are also input and output connections from the neocortex to other parts of the brain and nervous system. Though thin, the neocortex is folded in a manner that allows almost three square feet of neural tissue—about the size of a large pizza—to be packed into your skull.11 Different parts of the neocortex perform different functions. The occipital lobe is located at the very back of your head, and its cortex—the visual cortex—contains the main visual processing center of the brain.
A lot of what we know about the function of the occipital lobe comes from creatures in which that lobe has been damaged. You might look askance at someone who seeks to understand the function of the brakes on a car by driving one that doesn’t have any—but scientists selectively destroy parts of animals’ brains on the theory that one can learn what those parts do by studying animals in which they no longer do it. Since university ethics committees would frown on killing off parts of the brain in human subjects, researchers also comb hospitals seeking unfortunate people whom nature or an accident has rendered suitable for their study. This can be a tedious search because Mother Nature doesn’t care about the scientific usefulness of the injuries she inflicts. TN’s stroke was noteworthy in that it pretty cleanly took out just the visual center of his brain. The only drawback—from the research point of view—was that it affected only the left side, meaning that TN could still see in half his field of vision. Unfortunately for TN, that situation lasted for just thirty-six days. Then a tragic second hemorrhage occurred, freakishly destroying what was almost the mirror image of the first region.
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
