Cognitive Development

Piaget's Four Stages

The sensorimotor stage describes the years from birth to about age two. During this time the infant learns to coordinate the visual and tactile information she receives from the world around her with her emerging motor skills. For example, the child learns that by moving her eyes she can see a different part of her world and monitor how her arms or legs are interacting with various objects. Throughout these first two years of life the infant becomes increasingly aware of the world outside of herself and develops her ability to act on it.

The preoperational stage lasts from about two years of age until about six years of age. Piaget described preoperational children as egocentric; they have difficulty seeing the world from a perspective that is different from their own. A classic illustration of this was children's performance on Piaget and Bärbel Inhelder's three mountain task. Children viewed a three-dimensional display of three mountains from a particular perspective. Each mountain was slightly different in shape and had a small distinguishing reference object on top (e.g., a church steeple). The child was asked to select a two-dimensional picture that represented what another person would see from a different vantage point. Not surprisingly, the children were unsuccessful at seeing the display from another person's perspective. They often chose the picture of the mountains as they saw them from their own perspective.

FIGURE 1 Preschool children shown this diorama of three mountains with a distinctive landmark on each mountain were unable to say how the scene might look from perspectives other than the one they had adopted at the moment. (From Piaget & Inhelder, 1956.)

The third stage, concrete operations, lasts from about six years of age until about twelve years of age. In this stage, children become more flexible in their thinking and more able to perform concrete mental operations, such as conservation, which requires the simultaneous consideration of multiple pieces of information. In a typical task involving the conservation of liquid, water from a short, fat glass is poured into an empty glass that is tall and skinny. In order to understand that the volume of water does not change even though the level of the water does, the child must account for change in two different aspects at once: the circumference of the glass and the height of the liquid in that glass.

Piaget argued that in the formal operations stage children become even more flexible in their thinking and are able to think about the world more abstractly. During this final stage, from about twelve years of age through adolescence, children can think about hypothetical problems and give hypothetical solutions to those problems, such as how a society would maintain peace if there were no laws.

Critiques of Piaget's Theory

Piaget is widely recognized for his substantial contribution to the study of cognitive development. His experiments laid the foundation for much of the early work that examined cognitive development. During the 1970s and 1980s, however, much research questioned the timing of Piaget's stages. Because children vary widely as to when a particular stage starts or ends, it is unclear whether cognitive development occurs in stages, as Piaget's theory suggests, or whether it is a continuous process. Specifically, many researchers believe that Piaget underestimated the timing of some of children's abilities and that sometimes children understand a concept before they are able to demonstrate their understanding of it. This "competence performance gap" can occur when a child's motor skills are not advanced enough or their language skills are not sophisticated enough to indicate their knowledge and mental processes.

One example of a cognitive deficit inappropriately attributed to the preoperational stage of development involves object permanence. A child who understands object permanence realizes that an object continues to exist when it is moved out of sight. Some researchers suggest that a competence performance gap accounts for Piaget not finding evidence of object permanence in the sensorimotor stage. Piaget conducted the following experiment to examine an infant's understanding of object permanence. He showed an object such as a stuffed animal to an infant and then placed it behind an opaque screen that was in front of the infant. Piaget noticed that as soon as the object "disappeared" behind the screen the infant acted as if it had never existed and did not try to look behind the screen. Contrary to Piaget's suggestion that the infants in this study were unaware that the object still existed when it was out of view, some researchers have argued that these infants did indeed realize that the object existed, but that it was difficult for them to coordinate reaching around the screen with their memory for the object.

Researchers tested whether it was truly the difficulty of coordinating the motor skills or whether the children thought that out of sight was out of mind as Piaget had argued. Renee Baillargeon and her colleagues used a method different from Piaget's and were able to show that infants as young as four months old seemed to understand that an object that was out of sight still existed. Baillargeon used a methodology known as habituation, which exploits the tendency of infants to look at interesting displays until they become bored and look away. Thus, this method provides information about which objects in the environment capture an infant's attention without relying on their ability to coordinate motor movements. Subsequently, researchers can change a display in certain ways to examine whether the infant is sensitive to the change. Typically, a researcher records the length of time that an infant looks at the subsequent changed display. If the infant does not look at the second display for a longer amount of time than he looked at the first display, then the researcher concludes that the infant does not see this display as different from the original. If the infant does look for a longer amount of time, then it is assumed that he sees the subsequent display as novel and distinct from the first display.

To test this prediction, Baillargeon and Julie DeVos created a display that showed two events. In one display, a short carrot moved from one side of a screen to the other by passing behind an opaque screen. In the other scenario, a tall carrot passed behind the identical opaque screen. Once the infant habituated to the display, one of two different subsequent displays was shown: an "impossible" event in which the tall carrot passed behind a new screen containing a translucent window that should show the top of the carrot but did not, or a "possible" event showing the short carrot moving behind the screen where it just passed underneath the translucent window and was not seen until it came out on the other side. Because infants as young as four months looked longer at the "impossible" event than the "possible" event, Baillargeon suggested that the infants did remember the characteristics of the carrots and had expectations about whether they should appear in the window. Based on findings such as this, some researchers have argued that Piaget underestimated infants' understanding because he did not take into account the gap between the child's understanding and her ability to demonstrate that understanding. Piaget had contended that infants appear to understand object permanence at nine months old, which is when infants can coordinate their motor skills to successfully reach for a hidden object.

Piaget also seemed to underestimate children's ability to see the world from another person's viewpoint. Piaget used the three mountain task as evidence that children had difficulty taking another's perspective. The three mountain task, however, is not easy. Although the mountains are slightly different in size and have small distinguishing marks on the top, they are still quite similar in appearance. According to Helen Borke, when this task has been modified using a town scene that contains familiar animals and a number of different-shaped landmarks, children in the preoperational stage are successful at taking another person's perspective despite Piaget's contrary prediction.

During the 1980s and 1990s an area of research concerned with children's perspective-taking abilities engaged the field of cognitive development. This area focused on a child's "theory of mind," suggesting that children have theories for the way their minds work, as well as the way other people's minds work. Heinz Wimmer and Josef Perner developed a classic demonstration of children's "theory of mind." Using a task called the Maxi Chocolate Task, Wimmer and Perner told children a story about a child named "Maxi," who places a piece of chocolate in the kitchen cabinet and then goes out to play. While he is out to play, his mother moves the chocolate to another location. Later, Maxi comes home and he wants his chocolate. The test question to the child participant is, "Where will Maxi look for his chocolate?" Three-year-olds typically respond that Maxi will look for the chocolate in the second location, because they themselves know it is there and it is difficult for them to understand that their perspective is different from Maxi's. Alternatively, most four-year-olds and nearly all five-year-olds take the perspective of Maxi and answer that he will look for the chocolate in the kitchen cabinet where he left it because he does not know that his mother has moved it. Thus, contrary to Piaget's suggestion that only children between six and eight years of age will have developed a "theory of mind," this task has shown that four- and five-year-olds can take the perspective of another person.

Beyond Piaget

The work examining children's "theory of mind" is one example of how cognitive development research at the end of the twentieth century and the beginning of the twenty-first century has moved away from experiments designed to test Piaget's theory. Many researchers are no longer focused on showing which Piagetian tasks can be done earlier and instead focus on providing theoretical explanations for why and when children might be successful on certain tasks. Some of these studies employ modern neuro-imaging techniques (such as positron emission tomography, functional magnetic resonance imaging, and electrical encephalographic techniques) to examine the effects of cognitive development in the brain. For example, if psychologists using these techniques can map out when the various brain structures develop during childhood, it may become possible to predict when various skills and capabilities that rely on those structures will emerge. Another burgeoning area of research in cognitive development examines the influence of culture on cognition in order to test for the universality or uniqueness of development across cultures. For example, the study of culture is critical for investigating how language and thought may affect each other, understanding why some people believe intelligence is primarily innate and others believe it is primarily the product of effort, and determining how people may solve problems differently based on their cultural norms and ideals.