It's a Jungle in There: How Competition and Cooperation in the Brain Shape the Mind (20 page)

To pursue these ideas, they sutured one of the eyelids of their kitten subjects so the kittens received patterned visual input only through the exposed eye.
²⁸
Before the eyelids were sutured, the kittens’ visual cortex cells were equally sensitive to visual input from either eye. A given cell that was tuned to a visual stimulus entering the
left
eye, say, was, on average, just as sensitive as any given cell tuned to a comparable visual stimulus entering the
right
eye.

After suturing, things changed. A given cell that was initially tuned to visual input from the eye that was sutured became less sensitive to visual input to that eye. This was shown in tests where the eye that was shut was briefly exposed to visual stimuli. Many of the cells that were originally sensitive to visual input to the previously open eye lost their sensitivity. Meanwhile, those same cells became increasingly sensitive to visual input to the
other
eye, the one that stayed open.

What do these results reveal? They show that it’s a jungle in there. Inputs from the eye that remained open always “wanted” to connect with neurons that, initially, were mainly connected with the other eye. But without consistent input from the other eye (the eye whose lid was sutured in the experiment), those neurons became easy targets for inputs from the open eye.

Now you know why young pirates inhabit daycare centers. Kids with medically prescribed eye patches need help strengthening sight in their “weak” eyes. The strengthening can be achieved by pursuing the counterintuitive practice of restricting input from the stronger eye. When the stronger eye no longer dominates because it fails to receive visual stimulation, the weaker eye has a chance to strengthen its connections within the brain.
²⁹

A further aspect of the eye-patch procedure bears mentioning. This is the
critical period
effect. Within a certain time frame, the possibility of changing neural connectivity is high, but later it declines. One way to understand the critical period effect is to say that beyond some point in development, cooperation exceeds competition. Neural birds of a feather stick together so strongly that it’s hard to pull them apart. Owing to the critical period effect for vision, the pirates I’ve told you about are young rather than old. Older individuals are less likely to benefit from visual retraining.
³⁰

Just how critical is the critical period? It would be a mistake to conclude from the last section that the critical period is all-or-none. A safer conclusion is that the critical period is statistical. The chance of gaining or regaining use of an eye is higher during the critical period than afterward, but that doesn’t imply that the chance of regaining use of an eye drops to zero.

A demonstration of this more encouraging outcome came from a professor of neuroscience at Mount Holyoke College in South Hadley, Massachusetts: Susan Barry. Barry was cross-eyed as a child. Because of the misalignment of her eyes, the images coming from her left and right eyes failed to fuse in the normal way. As a result, her depth perception was askew.
³¹

Recall from earlier in this chapter that retinal disparity provides a cue to depth. In fact, retinal disparity is the main binocular depth cue. The slight offset of images cast on the left and right retinas by objects at different distances supplies observers with the most reliable source of visual information about how far away objects are. In the case of Susan Barry, retinal disparity was always huge, and as a result it didn’t provide a reliable cue to depth. As a girl, Susan learned, given this large retinal disparity, to alternate her attention
from one eye to the other—a common strategy among cross-eyed people. Given this alternation of attention, she could see with each eye, but with only one eye at a time. Deprived of the usual retinal disparity cues to depth, she saw a flat world.

Classical research in visual neuroscience, such as the research reviewed earlier in this chapter, suggested that individuals like Susan Barry would have no chance of gaining depth perception in adulthood. According to the classical, all-or-none, critical-period view, her neural connections relevant to depth perception would be choked off by the time she reached maturity. But Susan Barry disproved the classical conception.

As an adult, she embarked on a training procedure in which she learned to coordinate her eyes in a new way so she could aim both her eyes at the same place at the same time. What she discovered, as told in her book,
Fixing My Gaze: A Scientist’s Journey into Seeing in Three Dimensions
, was that she learned to see in 3D.

Susan Barry’s success in this venture proved that neural plasticity allowing for recovery of visual depth perception does not shut down once a putative critical period ends (around the time of puberty). Neural plasticity extends into adulthood.
³²

The effects of cooperation and competition on perceptual learning are not limited to inter-ocular communication. They also extend to other aspects of vision, and to other modalities. Within the visual modality, developmental changes similar to those described for the two eyes have been mapped out for sensitivity to visual tilt. The pioneering study was done by two neurophysiologists at Stanford University whose approach followed logic similar to Hubel and Wiesel’s.
³³
Instead of suturing single eyelids of kittens, the Stanford researchers restricted the visual inputs to each of their kittens’ eyes. The kittens wore special goggles that allowed one eye to see only horizontal lines and the other eye to see only vertical lines.

The result was that the receptive field properties of neurons in the kittens’ visual cortices became sensitive to the orientations to which each eye was exposed. If an eye was exposed to vertical lines, neurons with receptive fields for that eye became tuned to vertical lines. If an eye was exposed to horizontal lines, neurons with receptive fields for that eye became tuned to horizontal lines. Thus, the cells’ orientation sensitivities changed based on experience.

Effects like these are not limited to long-term learning via selective rearing methods in kittens. They’re also demonstrated through perceptual learning studies with people. In one experiment, adults with normal visual acuity judged the offsets of two vertical line segments.
³⁴
One line segment appeared above the other but was shifted slightly to the left or right. The observers’ task was to indicate whether the top line segment was to the left or right of the line below. After pressing the associated button, the observers got feedback about the accuracy of their responses. With practice, their visual acuity improved. The offsets the observers could detect got smaller and smaller. The same thing happened if the orientation of the line-segment pairs was horizontal rather than vertical. Now, after indicating whether a left line was higher or lower than a right line, observers were again told whether their decision was correct. The offsets they could detect got smaller and smaller with practice, indicating finer discrimination for line height.

The most interesting outcome came when the participants switched from judgments about vertical offsets to judgments about horizontal offsets, or vice versa. You might think that with practice at judging offsets, people would become experts at offset judging, no matter what the orientation of the stimuli. This is not what happened, however. After observers made judgments about horizontal offsets, they did poorly at making judgments about vertical offsets—worse, in fact, than observers who had never made the same vertical-offset judgments. The same thing happened for observers who first made vertical-offset judgments. They improved on those judgments, but if they switched to horizontal offsets, they did worse than observers who had never made those judgments.

How can you make sense of this outcome? You can infer that perceptual learning can be remarkably specific. It doesn’t always have to be, of course. Someone who develops a clear sense of what constitutes a good painting of a
landscape
may become adept at judging the quality of painted
portraits
. But in the case of judging offsets, people develop remarkably specialized perceptual abilities. The reason for this specialization is rooted in the neural basis of these judgments. Neurons get recruited for the specific judgments that are required. As a result, there is greater acuity for that kind of judgment but not others. Other, related judgments may be even become harder to make than usual if their neural territory was co-opted.
³⁵

Many other studies have been done on perceptual learning, and they, in turn, have demonstrated improved discrimination abilities that are often remarkably restricted. Models that have been developed to account for such changes have invariably resorted to internal competition and cooperation
among neural elements coding aspects of the inputs, typically in a redundant fashion. The models have assumed selective pressures causing some connections to get stronger and others to get weaker. As a result, someone who becomes an expert at judging certain kinds of stimuli can be said to house mental creatures that have become adept at responding well to those stimuli. Like creatures in the wild who become specialized for the niches they occupy, specialized neural ensembles develop to cope more expeditiously with some stimuli than others. The stimuli that are handled well are the ones that are regularly encountered. Seldom-encountered stimuli aren’t handled so well because few neural teams can claim those stimuli as niches.

These comments are meant to show that the jungle principle applies to perception and perceptual learning. I should mention in closing that I focused on vision in this chapter, but the jungle principle applies equally well to all sensory modalities, at least as far as I know.

While I was preparing this book, I attended a conference at a bucolic research institute in Bielefeld, Germany—the Zentrum für interdisziplinäre Forschung, also known as the ZiF, or the Center for International Research. The institute is located on the edge of a forest. It’s nestled among tall trees, and it fulfills most people’s idea of a scholar’s paradise. It’s lushly carpeted, beautifully furnished with a world-class library, and has a lobby adorned with paintings and sculptures honoring deep thinkers. Scholars at the institute work intently on their books and manuscripts, unfazed, apparently, by the outer jungle.

Even at a place like ZiF, however, just thinking isn’t enough. At the end of a scholar’s stay there (typically at the end of a sabbatical), he or she is asked to submit a list of accomplishments. “Had deep thoughts” doesn’t get lots of credit. “Wrote six journal articles and a book” carries more weight.

I’m telling you this partly to dispel the myth that scholars merely think for a living. They don’t. They write grant applications, scramble for book contracts, angle for speaking engagements, and so on. Even the deepest thinkers must communicate their ideas. Being lost in thought does scholars little good—as little good, in fact, as for anyone working in the “real world.”

Doing nothing because you’re lost in thought is quite different from doing nothing because you can’t move. If you can’t express yourself no matter how much you want to, that can be frustrating. If you can’t reach for something that you must take hold of, that inability can cost you your life.

Stories of people who can’t move can be gripping. You may have seen the movie
127 Hours
, a film about a mountain climber whose arm gets caught under a boulder. What the climber does to finally free himself is hard even to contemplate: He cuts off his own arm. This awful act takes incredible bravery. The planning the climber must do to carry out the unspeakable act reflects the need for painstaking, not to mention pains-
making
, problem-solving. To complete the self-amputation, he has to solve many problems, some physical and others emotional. In the end, he has to bring himself to a mental place where, to escape
from where he was—literally between a rock and a hard place—he must do what few of us can even imagine doing.

Not all physical problems require such intense preparation. If you reach for a glass and move it to another location, you have a physical problem to solve, though you hardly notice that you do, at least if you’re an adult with normal neuromuscular control. You can grasp the glass virtually anywhere, and you can take hold of the glass with any of an infinite number of body positions—with your elbow extended or with your elbow bent, with your hand high on the glass or with your hand low down, and so on. You don’t need to think about which grasp to use, but by the time you’ve grasped the glass, you’ve implicitly chosen one of the infinite number of grasps that was possible.

It turns out that where and how you grasp a glass depends on what you plan to do with it. If you plan to carry the glass to a high position, you’ll probably grasp it low, but if you plan to carry it to a low position, you’ll probably grasp it high.
¹
This change of behavior reflects planning of future body states. Similarly, if you plan to turn the glass over, rotating it 180 degrees in order to fill it with water, you’ll probably grasp the glass with your thumb pointing
down
—a posture you’d be unlikely to adopt otherwise.
²
Young children don’t appreciate this rule for grasping. They tend to grasp glasses or other objects thumb-up as they prepare to turn the glasses over, even if this leaves them in a relatively awkward thumb-down posture at the end.
³

These observations suggest that everyday physical actions require planning.
⁴
How well you plan reflects how skilled you are, and how skilled you are is manifested in virtually everything in you do. In athletics, for example, what makes a basketball player great is not just that s/he can make foul shots reliably. It’s also that s/he can determine, on the spur of the moment, how to get the ball to a teammate or to the basket. What makes a skier skillful is not just that s/he can descend the same slope over and over again without falling. It’s that s/he can cope with the vicissitudes of the snow, the vagaries of the wind, and the variations of his or her own body. If the skier has just sprained an ankle but can still slalom down the course in record time, s/he’s a champion.