Incognito (4 page)

Freud’s intuition about the unconscious brain was spot-on, but he lived decades before the modern blossoming of
neuroscience. We can now peer into the human cranium at many levels, from electrical spikes in single cells to patterns of activation that traverse the vast territories of the brain. Our modern technology has shaped and focused our picture of the inner cosmos, and in the following chapters we will travel together into its unexpected territories.

How is it possible to get angry at yourself: who, exactly, is mad at whom? Why do rocks appear to climb upward after you stare at a waterfall? Why did Supreme Court Justice William Douglas claim that he was able to play football and go hiking, when everyone could see that he was paralyzed after a stroke? Why was Topsy the elephant electrocuted by
Thomas Edison in 1916? Why do people love to store their money in Christmas accounts that earn no interest? If the drunk
Mel Gibson is an anti-Semite and the sober Mel Gibson is authentically apologetic, is there a real Mel Gibson? What do Ulysses and the subprime mortgage meltdown have in common? Why do strippers make more money at certain times of month? Why are people whose name begins with J more likely to marry other people whose name begins with J? Why are we so tempted to tell a secret? Are some marriage partners more likely to cheat? Why do patients on Parkinson’s medications become compulsive gamblers? Why did
Charles Whitman, a high-IQ bank teller and former Eagle Scout, suddenly decide to shoot forty-eight people from the University of Texas Tower in Austin?

What does all this have to do with the behind-the-scenes operations of the brain?

As we are about to see, everything.

One afternoon in the late 1800s, the physicist and philosopher
Ernst Mach took a careful look at some uniformly colored strips of paper placed next to each other. Being interested in questions of perception, he was given pause by something: the strips did not look quite right. Something was amiss. He separated the strips, looked at them individually, and then put them back together. He finally realized what was going on: although each strip in isolation was uniform in color, when they were placed side by side each appeared to have a gradient of shading: slightly lighter on the left side, and slightly darker on the right. (To prove to yourself that each strip in the figure is in fact uniform in brightness, cover up all but one.)
¹

Mach bands.

Now that you are aware of this illusion of “
Mach bands,” you’ll notice it elsewhere—for example, at the corner where two walls meet, the lighting differences often make it appear that the paint is lighter or darker right next to the corner. Presumably, even though the perceptual fact was in front of you this entire time, you have missed it until now. In the same way, Renaissance painters noticed at some point that distant mountains appeared to be tinted a bit blue—and once this was called out, they began to paint them that way. But the entire history of art up to that point had missed it entirely, even though the data was unhidden in front of them. Why do we fail to perceive these obvious things? Are we really such poor observers of our own experiences?

Yes. We are astoundingly poor observers. And our
introspection is useless on these issues: we believe we’re seeing the world just fine until it’s called to our attention that we’re not. We will go through a process of learning to observe our experience, just as Mach carefully observed the shading of the strips. What is our conscious experience
really
like, and what is it not like?

Intuition suggests that you open your eyes and voilà: there’s the world, with all its beautiful reds and golds, dogs and taxicabs, bustling cities and floriferous landscapes.
Vision app
ears effortless and, with minor exceptions, accurate. There is little important difference, it might seem, between your eyes and a high-resolution digital video camera. For that matter, your ears seem like compact microphones that accurately record the sounds of the world, and your fingertips appear to detect the three-dimensional shape of objects in the outside world. What intuition suggests is dead wrong. So let’s see what’s really happening.

Consider what happens when you move your arm. Your brain depends on thousands of nerve fibers registering states of contraction and stretching—and yet you perceive no hint of that lightning storm of neural
activity. You are simply aware that your limb
moved and that it is somewhere else now.
Sir Charles Sherrington, an early neuroscience pioneer, spent some time fretting about this fact during the middle of the last century. He was awestruck by the lack of awareness about the vast mechanics under the surface. After all, despite his considerable expertise with nerves, muscles, and tendons, he noted that when he went to pick up a piece of paper, “I have no awareness of the muscles as such at all.… I execute the movement rightly and without difficulty.”
²
He reasoned that if he were not a neuroscientist it would not have occurred to him to suspect the existence of nerves, muscles, and tendons. This intrigued Sherrington, and he finally inferred that his experience of moving his arm was “a mental product.… derived from elements which are not experienced as such and yet … the mind uses them in producing the percept.” In other words, the storm of nerve and muscle activity is registered by the brain, but what is served up to your awareness is something quite different.

To understand this, let’s return to the framework of consciousness as a national newspaper. The job of a headline is to give a tightly compressed summary. In the same manner, consciousness is a way of projecting all the activity in your nervous system into a simpler form. The billions of specialized mechanisms operate below the radar—some collecting sensory data, some sending out motor programs, and the majority doing the main tasks of the neural workforce: combining information, making predictions about what is coming next, making decisions about what to do now. In the face of this complexity, consciousness gives you a summary that is useful for the larger picture, useful at the scale of apples and rivers and humans with whom you might be able to mate.

The act of “seeing” appears so natural that it is difficult to appreciate the vastly sophisticated machinery underlying the process. It may come as a surprise that about one-third of the human
brain is devoted to vision. The brain has to perform an enormous amount of work to unambiguously interpret the billions of photons streaming into the eyes. Strictly speaking, all
visual scenes are ambiguous: for example, the image to the right can be caused by the Tower of Pisa at a distance of five hundred yards, or a toy model of the tower at arm’s length: both cast the identical image on your eyes. Your brain goes through a good deal of trouble to disambiguate the information hitting your eyes by taking context into account, making assumptions, and using tricks that we’ll learn about in a moment. But all this doesn’t happen effortlessly, as demonstrated by patients who surgically recover their eyesight after decades of blindness: they do not suddenly see the world, but instead must
learn
to see again.
³
At first the world is a buzzing, jangling barrage of shapes and colors, and even when the optics of their eyes are perfectly functional, their brain must learn how to interpret the data coming in.

For those of us with a lifetime of sight, the best way to appreciate the fact that vision is a construction is by noticing how often our visual systems get it wrong. Visual
illusions exist at the edges of what our system has evolved to handle, and as such they serve as a powerful window into the brain.
⁴

There is some difficulty in rigorously defining “illusion,” as there is a sense in which all of vision is an illusion. The resolution in your peripheral vision is roughly equivalent to looking through a frosted shower door, and yet you enjoy the illusion of seeing the periphery clearly. This is because everywhere you aim your central vision appears to be in sharp focus. To drive this point home, try this demonstration: have a friend hold a handful of colored markers or highlighters out to his side. Keep your gaze fixed on his nose, and now try to name the order of the colors in his hand. The results are surprising: even if you’re able to report that there are some colors in your periphery, you won’t be able to accurately
determine their order. Your peripheral vision is far worse than you would have ever intuited, because under typical circumstances your brain leverages the eye muscles to point your high-resolution central vision directly toward the things you’re interested in. Wherever you cast your eyes appears to be in sharp focus, and therefore you assume the whole visual world is in focus.
^*

That’s just the beginning. Consider the fact that we are not aware of the
boundaries
of our visual field. Stare at a point on the wall directly in front of you, stretch your arm out, and wiggle your fingers. Now move your hand slowly back toward your ear. At some point you can no longer see your fingers. Now move it forward again and you can see them. You’re crossing the edge of your visual field. Again, because you can always aim your eyes wherever you’re interested, you’re normally not the least bit aware that there are boundaries beyond which you have no vision. It is interesting to consider that the majority of human beings live their whole lives unaware that they are only seeing a limited cone of vision at any moment.

As we dive further into vision, it becomes clear that your brain can serve up totally convincing perceptions if you simply put the right keys in the right locks. Take the perception of depth. Your two eyes are set a few inches apart, and as a result they receive slightly different images of the world. Demonstrate this to yourself by taking two photographs from a few inches apart, and then putting them side by side. Now cross your eyes so that the two photos merge into a third, and a picture will emerge
in depth
. You will genuinely experience the depth; you can’t shake the perception. The impossible notion of depth arising from a flat image divulges the mechanical, automatic nature of the computations in the visual system: feed it the right inputs and it will construct a rich world for you.

Cross your eyes: the two images feed your brain the illusory signal of depth.

One of the most pervasive mistakes is to believe that our visual system gives a faithful representation of what is “out there” in the same way that a movie camera would. Some simple demonstrations
can quickly disabuse you of this notion. In the figure below, two pictures are shown.