PIAGET ’S STAGE THEORY
According to Piaget, the child relies on a different type of thinking than an adult does. In Piaget’s view, adult thinking emerges only after the child has moved through a series of stages of intellectual growth (Figure 14.8). They are the sensorimotor period (from birth to about 2 years), the preoperational period (roughly 2 to 7 years), the concrete operational period (7 to 12 years), and the formal operational period (approximately 12 years and up).
During the sensorimotor period, Piaget argued, the infant’s world consists of his own sensations. Therefore, when an infant looks at a rattle, he is aware of looking at the rattle but has no conception of the rattle itself existing as a permanent, independent object. If the infant looks away from the rattle (and thus stops seeing it), then the rat-tle ceases to exist. It is not just “out of sight, out of mind”—it is “out of sight, out of existence.” In this way, Piaget claimed, infants lack a sense of object permanence—the understanding that objects exist independent of our momentary sensory or motoric interactions with them.
Piaget developed this view based on his observation that infants typically look at a new toy with delight, but if the toy disappears from view, they show little concern (Figure 14.9). At a slightly later age, infants might show signs of distress when the toy disappears, but they still make no effort to retrieve it. This is true even if it seems perfectly obvious where the toy is located. For example, an experimenter might drape a light cloth over the toy while an infant is watching. In this situation, the toy is still easily within reach and its shape is still (roughly) visible through the folds of the cloth. The child watched it being covered just moments earlier. But still the infant makes no effort to retrieve it.
At about 8 months, infants do start to search for toys that have been hidden, but even then, their searching shows a peculiar limitation. Suppose, that a 9-month-old sees an experimenter hide a toy monkey under a cover located, say, to the child’s right. The child will happily push the cover off and snatch up the monkey. The experimenter now repeats the process a few times, always hiding the monkey under the same cover to the child’s right. Again and again the child pulls the cover off and retrieves the monkey. But now the experimenter changes the procedure slightly. Very slowly and in full view of the child, she hides the toy in a different place, say, under a cover to the child’s left. The child closely watches her every movement—and then does exactly what he did before. He searches under the cover on the right, even though he saw the experimenter hide the toy in another place just a moment earlier.
This phenomenon is often called the A-not-B effect, where A designates the place where the object was first hidden and B the place where it was hidden last (Figure 14.10). Why does this peculiar error occur? Piaget (1952) argued that the 9-month-old still has not grasped the fact that an object’s existence is independent of his own actions. Thus, the child believes that his reaching toward place A (where he found the toy previously) is as much a part of the monkey as the monkey’s tail is. In effect, then, the child is not really searching for a monkey; he is searching for the-monkey-that-I-find-on-the-right. No wonder, there-fore, that the child continues searching in the same place.
According to Piaget, a major accomplishment of the sensorimotor period is coming to understand that objects exist on their own—even when they are not reached for, seen, heard, or felt. Piaget held that what makes this accomplishment possible is the infant’s increasingly sophisticated schemas—ways of interacting with the world and (at a later stage of development) ways of interacting with ideas about the world.
Piaget believed that newborns start life with very few schemas, and these tend to involve the infant’s built-in reactions, such as sucking or grasping. In Piaget’s view, these action pat-terns provide the infant’s only means of responding to the world, and thus they provide the first mental categories through which infants organize their world. Infants understand the world, in other words, as consisting of the suckables, the graspables, and so on.
Across the first few months of life, though, the child refines and extends these schemas and learns how to integrate them into more complex ways of dealing with the world. This evolution, according to Piaget, depends on two processes that he claimed were responsible for all cognitive development: assimilation and accommodation. In the process of assimilation, children use the mental schemas they have already formed to interpret (and act on) the environment; in other words, they assimilate objects in the environment into their existing schemas. In the process of accommodation, the child’s schemas change as a result of his experiences interacting with the world; that is, the schemas accommodate to the environment (Figure 14.11).
Through the processes of assimilation and accommodation, the child refines and differentiates her schemas, which gradually leads her to create a range of new schemas that enhance her ability to interact with the world. In addition, as the child becomes increasingly skilled at using schemas, she eventually becomes able to use more than one schema at a time—reaching while looking, grasping while sucking. Coordinating these individual actions into one unified exploratory schema helps to break the connection between an object and a specific way of acting on or experiencing that object. This liberation of the object from a specific action, in turn, helps propel the child toward understanding the object’s independent existence—that is, it helps propel her toward object permanence and a mature understanding of what an object is.
Piaget believed that the sensorimotor period ends when children achieve object per-manence (and, thus, the capacity for representational thought) at roughly 2 years of age. But, even so, the mental world of 2-year-olds is, in Piaget’s view, a far cry from the world of adults. This is because 2-year-olds have not yet learned how to interrelate their mental representations in a coherent way. Piaget referred to the manipulation of men-tal representations as operations, and thus dubbed the period from age 2 to 7, before these mental operations are evident, as the preoperational period.
A revealing example of preoperational thought is the young child’s apparent failure to conserve quantity. One procedure demonstrating this failure uses two identical glasses, A and B, which stand side by side and are filled with the same amount of liq-uid. The experimenter then asks the child whether there is more liquid in one glass or the other, then obligingly adds a drop here, a drop there until the child is completely satisfied that there is “the same to drink in this glass as in that.”
The next step involves a new glass, C, which is taller but narrower than A and B (Figure 14.12). While the child is watching, the experimenter pours the entire contents of glass A into glass C. She then points to B and C and asks, “Is there more in this glass or in that, or are they the same?” To an adult, the amounts are obviously identical, since A was completely emptied into C, and A and B were made equal at the outset. But 4- or 5-year-olds insist that there is more liquid in C. When asked for their reason, they explain that the liquid comes to a much higher level in C. They seem to think that the amount has increased as it was transferred from one glass to another. They are too impressed by the visible changes in liquid level to realize that the amount nonetheless remains constant.
In the preoperational period, children also fail tests that depend on the conservation of number. In one such test, the experimenter first shows the child two rows of pennies, and the child agrees that both rows contain the same number of coins. The experimenter then rearranges one row by spacing the pennies farther apart. Prior to age 5 or 6, chil-dren generally assert that there are now more coins in this row because “they’re more spread out.” But from about age 6 on, the child has no doubt that there are just as many coins in the tightly spaced row as there are in the spread-out line.
Why do preschool children fail to conserve? According to Piaget, part of the problem is their inability to interrelate the different dimensions of a situation. To conserve liquid quantity, for example, the children must first comprehend that there are two relevant factors: the height of the liquid column, and the width of the glass. They must then appreciate that a decrease in the column’s height is accompanied by an increase in its width. Thus, the children must be able to attend to both dimensions simultaneously and relate the dimensions to each other. They lack this capacity, since it requires using a higher-order schema to combine initially discrete aspects of a percep-tual experience into one conceptual unit.
By age 7 or so, once children have learned how to interrelate their mental represen-tations, they enter the concrete operational period. They now grasp the fact that changes in one aspect of a situation can be compensated for by changes in some other aspect. They are also able to transform their own mental representations in a variety of ways and thus understand, for example, what would happen if the liquid were poured back into its original glass. But according to Piaget, children’s intellectual capacities are still limited in an important way: They can apply their mental operations only to con-crete objects or events (hence the term concrete operations). It is not until age 11 or 12 that formal operations are possible, and we will consider this stage in the following sec-tion on adolescence.