The Story of Psychology (72 page)

And so it goes, on and on. At times, the evolutionary psychologists sound as if their discipline will provide fundamental understandings not just of development but of practically everything within traditional psychology. David Buss, for one, sees it as “a scientific revolution that will
provide the foundation for psychology in the new millennium…the metatheory that seeks to present a unified understanding of the mechanisms of the mind.”
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Steven Pinker of Harvard has said that “in the study of humans, there are major spheres of human experiences— beauty, motherhood, kinship, morality, cooperation, sexuality, violence— in which evolutionary psychology provides the only coherent theory.”
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To be sure, there are other candidates for a metatheory that will provide a unified mental science; more of that later. Meanwhile, we have gone far afield from development, to which, after a final word about Piaget, we return.

About Piaget: Many developmentalists, while accepting his general conception of human development, now consider his scheme of stages physiologically limited and culturally biased. A number of modified stage theories have been advanced, but it is unclear which one will eventually dominate the field. Whichever one does, however, it will embody Piaget’s fundamental concepts but go far beyond them, even as Einstein’s physics embodied but went far beyond Newton’s.

Despite Piaget’s training in the natural sciences and his early decision to explore the biological explanation of knowledge, his theory deals almost entirely with development through cognitive processes; he either ignores the role of maturation—the growth processes of the body that automatically cause changes in behavior—or takes it for granted. But for some years many developmentalists have felt that until the part that maturation plays in psychological development is fully spelled out, we cannot know to what extent behavior is innate rather than acquired by means of assimilation and accommodation.

Yet how is one to distinguish between the two influences? From the infants’ first day outside the womb they are learning as well as maturing; isolating the results of each process is a scientific problem of the first order. Newborns do, to be sure, possess important reflexes at birth that cannot owe anything to learning, such as turning their head toward a touch on the cheek as if in search of the nipple before they have ever known a nipple. And as most parents know, if you stick out your tongue at infants only one to three weeks old, they reflexively stick out their own tongues, an inherent reaction produced by “mirror neurons” that have recently been identified by brain scans and located as being in the pre-motor
cortex. But in general most changes in behavior or new forms of behavior may come either from maturation or learning or both.

Sometimes, however, nature accidentally provides an experiment that separates the two. Infants begin to babble at three or four months as a preparation for speech—but so do deaf children, obviously not in an effort to imitate heard speech but for some other reason. Babbling is evidently a form of programmed behavior that owes nothing to experience but begins spontaneously when the neural centers that direct it reach a certain stage of development. In normal children, babbling changes through learning, coming more and more to resemble the sounds and intonations of speech; in deaf children it slowly disappears from lack of learning.
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Since opportunities to observe behavioral development in the absence of learning are rare, during the early years of the specialty a few developmental psychologists made history by creating the conditions experimentally. In 1932, Myrtle McGraw, then at the Columbia-Presbyterian Medical Center in New York, got a low-income Brooklyn family to lend her their twin boys for an experiment. For two years Johnny and Jimmy, apparently identical twins, spent eight hours a day, five days a week, in McGraw’s laboratory. Johnny got extensive training in physical skills; Jimmy remained in his crib “undisturbed” (not even played with) and with only two toys at a time. Johnny, before he was a year old, could climb a steep incline, swim under water, and rollerskate; Jimmy could do none of these (but had become as adept as Johnny at grasping objects, sitting alone, and walking). Photographs taken by McGraw show Johnny, at twenty-one months of age, boldly letting himself down from a five-foot stand, hanging by his hands, and dropping to a mattress; Jimmy, crouched on a much shorter stand, stares down and refuses to budge.
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At the end of two years McGraw gave Jimmy intensive training to see whether he could catch up to Johnny; he never fully did. But psychologists who have reviewed her data feel that Johnny’s training gave him only a small and largely temporary advantage over Jimmy. McGraw did not agree; many years later—after experiments like hers, which stunt a child’s development, had come to be considered gravely unethical—she asserted that although Jimmy had caught up in most ways, even as a young adult he still had less ease and grace of physical movement than Johnny.
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What this proves, however, is hard to say, since it turned out that the boys were fraternal twins, not identicals. The only safe conclusion is that intensive physical training can push a child to achieve physical skills ahead of schedule and that most of the gain is temporary.

A more drastic experiment was conducted, also beginning in 1932, by Wayne Dennis, then at the University of Virginia. From an indigent Baltimore woman he obtained her fraternal twin girls, Del and Rey, when they were five weeks old, and, with his wife’s help, reared them in his home for over a year. His plan was to deprive them of all stimulation and learning to see what forms of behavior arose spontaneously with maturation. In a journal article, Dennis reported, with no qualms or apologies, how he carried out his experiment:

During the first six months we kept a straight face in the babies’ presence, neither smiling nor frowning, and never played with them, petted them, or tickled them, except as these actions reasonably were incorporated into routine experiments…To restrict practice which might influence sitting, the infants were kept almost continually on their backs in the cribs.
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They were not even allowed toys or the sight of each other for eleven months. (There was a screen between their cribs.)

The results, Dennis claimed, showed that “the infant within the first year will ‘grow up’ of his own accord,” as evidenced in the twins by such behavior as laughing, bringing their feet to their mouths, and crying in response to sounds at about the same ages as children reared normally. But they lagged far behind other children in crawling, sitting, and standing. After fourteen months Dennis gave them a period of training that, he said, quickly brought them up to normal. By his own admission, however, Rey could not walk without holding on until her seventeenth month and Del not until her twenty-sixth month.

The twins spent the rest of their childhood in institutions and the homes of relatives. Although Dennis claimed he had brought them up to par, he later had good reason to doubt it. In Iran he studied orphanage children and found that many of them, neglected and given little attention, were developmentally retarded at two years and remained somewhat so in adolescence. But he never followed up on Del and Rey to see how they turned out; perhaps he did not want to know.

Such experiments, rare seventy years ago, are nonexistent today; after the civilized world learned of the “medical research” conducted by Nazi doctors in concentration camps, legal constraints on research with human subjects became stringent. But developmentalists have pursued
their goals in other ways. One is by experimenting with animals. Much as behaviorists sought principles of learning in rats that would be relevant to learning in humans, developmentalists sought principles of maturation in animals that would apply to humans.

In one well-known case, newly hatched goslings, which were thought to trail after their mother instinctively, were taught by the German ethologist and Nobelist Konrad Lorenz to follow him instead. Lorenz arranged to be the only moving creature the goslings saw during their first days. Their instinct being to follow a moving object, they followed him—and having learned to do so, ignored their mother when they later saw her. Lorenz theorized that at a “critical period” of maturation, the image of the creature being followed becomes fixed in the nervous system. Nature meant it to be the mother goose and failed to anticipate the meddling of an ethologist.
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Eckhard Hess, an American, built a moving, quacking, decoy mallard, and put mallard ducklings in its presence. If he did so as soon as they were hatched, half of them became attached to it, but if he first did so when they were thirteen to sixteen hours old, over 80 percent became attached to it. What looked like an instinct was a more complex phenomenon: the nervous system of the duckling is wired to respond to moving objects but is most readily “imprinted” on a particular target at a special time slot in the maturation process.
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As a result of these findings, in the 1970s some developmentalists and pediatricians came to believe that it is in the first hours after birth that the mother-infant bond can best be formed. They advised mothers to cuddle the newborn against their naked body for a while immediately after delivery instead of having it whisked away to be cleaned up and parked in a bassinet in the hospital nursery. But while some subsequent research showed stronger infant-mother bonding when this was done, it was the mother who was bonded. Much other research has shown that the infant’s attachment to the mother (or father or other principal caretaker) develops over a period of four to five months in response to innumerable acts of caretaking and expressive attention.
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Much maturation research is concerned with physical skills and physical attributes, and adds little to our knowledge of the growth of the mind. But research on the development of perceptual abilities has been providing solid factual answers, in place of speculation, to the ancient central
question of psychology: How much is due to nature and how much to nurture (or, in developmental terms, to maturation and to learning)?

The work has been focused on early infancy, when perceptual abilities evolve rapidly; its aim is to discover when each new ability first appears, the assumption being that at its first appearance, the new ability arises not from learning but from maturation of the optic nervous structures and especially of that part of the brain cortex where visual signals are received and interpreted.

Much has been learned by simply watching infants—noting, for instance, at what age they can fix their gaze on nearby objects. But such observations leave many questions unanswered. What, exactly, do very young infants see? Not much, apparently; their eyes often seem unfocused and do not even track a moving object. On the other hand, mothers know that their infants gaze steadily at them while they nurse. Since we cannot ask them what they see, how can we find out?

In 1961, the psychologist Robert Fantz devised the ingenious method of doing so briefly mentioned earlier. He designed a stand in which, on the bottom level, the baby lies on his back, looking up. A few feet above is a display area where the experimenter puts two large cards, each containing a design—a white circle, a yellow circle, a bull’s-eye, a simple sketch of a face. The researcher, peering down through a tiny peephole (so that he is not visible), can watch the movement of the baby’s eyes and time how long they are directed at one or the other of each pair of patterns. Fantz found that at two months babies looked twice as long at a bull’s-eye as at a circle of solid color, and twice as long at a sketch of a face as at a bull’s-eye. Evidently, even a two-month-old can distinguish major differences and direct his gaze toward what he finds more interesting.
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Using this technique and others of a related nature, developmental psychologists have learned a great deal about what infants see and when they begin to see it. Some of what the psychologists learned: In the first week infants distinguish light and dark patterns; during the first month they begin to track slowly moving objects; by the second month they begin to have depth perception, coordinate the movement of the two eyes, and differentiate among hues and levels of brightness; by three months they can glance from one object to another, and can distinguish among family members; by four months they focus at varying distances, make increasingly fine distinctions (they look longer at an oblique angle they have not seen before than at an acute angle they have seen a number
of times), and begin to recognize the meaning of what they see (they look longer at a normal sketch of a face than at one in which the features have been scrambled and are in unnatural positions); and from four to seven months they achieve stereopsis, recognize that a shape held at different angles is still the same shape, and gain near-adult ability to focus at varying distances.
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A mass of comparable studies have been conducted, over the past half century, on the development of hearing, including the emergence of pitch and volume discrimination, discrimination among voices, and recognition of the direction a sound is coming from.

Exactly how maturation and experience interact in the brain tissues to produce such developmental changes is becoming clear from recent and current neuroscience research. Microscopic examination of the brains of infants who have died shows that in the first months of life a profusion of dendrites (branches) grow from its neurons and make contact with each other, as shown in Figure 19 (see page 433). This burgeoning continues apace; during the first two years of life the brain triples in size and the synaptic connections among the neurons reach astronomical numbers. (The rat’s brain, it has been estimated, forms a quarter of a million synapses—connections between nerve cells—every
second
during the first month of its life. In the human brain during the first months and years of life the rate of synaptic formation must be very many times greater.)