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Considering how exhaustively the brain has been studied, and for how long, it is remarkable how much elemental stuff we still don’t know or at least can’t universally agree upon. Like what exactly is consciousness? Or what precisely is a thought? It is not something you can capture in a jar or smear on a microscopic slide, and yet a thought is clearly a real and definite thing. Thinking is our most vital and miraculous talent, yet in a profound physiological sense we don’t really know what thinking is.
Much the same could be said of memory. We know a good deal about how memories are assembled and how and where they are stored, but not why we keep some and not others. It clearly has little to do with actual value or utility. I can remember the entire starting lineup of the 1964 St. Louis Cardinals baseball team—something that has been of no importance to me since 1964 and wasn’t actually very useful then—and yet I cannot recollect the number of my own cell phone, or where I parked my car in any large parking lot, or what was the third of three things my wife told me to get at the supermarket, or any of a great many other things that are unquestionably more urgent and necessary than remembering the starting players for the 1964 Cardinals (who were, incidentally, Tim McCarver, Bill White, Julian Javier, Dick Groat, Ken Boyer, Lou Brock, Curt Flood, and Mike Shannon).
So there is a huge amount we have left to learn and many things we may never learn. But equally some of the things we do know are at least as amazing as the things we don’t. Consider how we see—or, to put it slightly more accurately, how the brain tells us what we see.
Just look around you now. The eyes send a hundred billion signals to the brain every second. But that’s only part of the story. When you “see” something, only about 10 percent of the information comes from the optic nerve. Other parts of your brain have to deconstruct the signals—recognize faces, interpret movements, identify danger. In other words, the biggest part of seeing isn’t receiving visual images; it’s making sense of them.
For each visual input, it takes a tiny but perceptible amount of time—about two hundred milliseconds, one-fifth of a second—for the information to travel along the optic nerves and into the brain to be processed and interpreted. One-fifth of a second is not a trivial span of time when a rapid response is required—to step back from an oncoming car, say, or to avoid a blow to the head. To help us deal better with this fractional lag, the brain does a truly extraordinary thing: it continuously forecasts what the world will be like a fifth of a second from now, and that is what it gives us as the present. That means that we never see the world as it is at this very instant, but rather as it will be a fraction of a moment in the future. We spend our whole lives, in other words, living in a world that doesn’t quite exist yet.
The brain tricks you in a lot of ways for your own good. Sound and light reach you at very different speeds—a phenomenon we experience every time we hear a plane passing overhead and look up to find the sound coming from one part of the sky and a plane moving silently through another. In the more immediate world around you, your brain normally irons out these differences, so that you sense all stimuli as reaching you simultaneously.
In a similar way, the brain manufactures all the components that make up our senses. It is a strange, nonintuitive fact of existence that photons of light have no color, sound waves no sound, olfactory molecules no odors. As James Le Fanu has put it, “While we have the overwhelming impression that the greenness of the trees and the blueness of the sky are streaming through our eyes as through an open window, yet the particles of light impacting on the retina are colourless, just as the waves of sound impacting on the eardrum are silent and scent molecules have no smell. They are all invisible, weightless, subatomic particles of matter travelling through space.” All the richness of life is created inside your head. What you see is not what is but what your brain tells you it is, and that’s not the same thing at all. Consider a bar of soap. Has it ever struck you that soap lather is always white no matter what color the soap is? That isn’t because the soap somehow changes color when it is moistened and rubbed. Molecularly, it’s exactly as it was before. It’s just that the foam reflects light in a different way. You get the same effect with crashing waves on a beach—greeny-blue water, white foam—and lots of other phenomena. That is because color isn’t a fixed reality but a perception.
You have probably at some time or other encountered one of those illusion tests that require you to stare for fifteen or twenty seconds at a red square, then shift your vision to a blank sheet of paper, and for a few moments you will see a ghostly square of greenish blue on the white paper. This “afterimage” is a consequence of tiring some of the photoreceptors in your eyes by making them work extra intently, but what is relevant is that the greenish-blue color is not there and has never existed anywhere but in your imagination. In a very real sense, that is true of all colors.
Your brain is also extraordinarily good at finding patterns and determining order in chaos, as these two well-known illusions show:
In the first illustration, most people see only random smudges until it is pointed out to them that the picture contains a dalmatian dog; then suddenly for nearly everyone the brain fills in the missing edges and makes sense of the whole composition. The illusion dates from the 1960s, but no one seems to have kept a record of who first created it.
The second illustration does have a known history. It is called a Kanizsa triangle, after the Italian psychologist Gaetano Kanizsa, who created it in 1955. There is of course no actual triangle in the picture, except for the one your brain puts there.
Your brain does all these things for you because it is designed to help you in every way it can. Yet paradoxically it is also strikingly unreliable. Some years ago, a psychologist at the University of California at Irvine, Elizabeth Loftus, discovered that it is possible through suggestion to implant entirely false memories in people’s heads—to convince them that they were traumatically lost in a department store or shopping mall when they were small or that they were hugged by Bugs Bunny at Disneyland—even though these things never happened. (Bugs Bunny is not a Disney character and has never been at Disneyland.) She could show many people pictures of themselves as a child in which the image had been manipulated to make them look as if they were in a hot-air balloon, and often the subjects would suddenly remember the experience and excitedly describe it, even though in each case it was known that it had never happened.
Now, you might think that you could never be that suggestible, and you would probably be right—only about one-third of people are that gullible—but other evidence shows that we all sometimes completely misrecall even the most vivid events. In 2001, immediately after the 9/11 disaster at the World Trade Center in New York, psychologists at the University of Illinois took detailed statements from seven hundred people about where they were and what they were doing when they learned of the event. One year later, the psychologists asked the same question of the same people and found that nearly half now contradicted themselves in some significant way—put themselves in a different place when they learned of the disaster, believed that they had seen it on TV when in fact they had heard it on the radio, and so on—but without being aware that their recollections had changed. (I, for my part, vividly recall watching the events live on television in New Hampshire, where we were then living, with two of my children, only to learn later that one of those children was in fact in England at the time.)*3