FOCUS ON RESEARCH What Do Infants Know About Physics
352 Chapter 9 Human Development In the years since Piaget’s death, psychologists have found new ways to measure what is going on in infants’ minds. They use infrared photography to record infants’ eye movements, time-lapse photography to detect slight hand movements, special equipment to measure infants’ sucking rates, and computer technology to track and analyze it all. Their research shows that infants know a lot more, and know it sooner, than Piaget ever thought they did (Onishi & Baillargeon, 2005). For example, it turns out that infants in the sensorimotor period are doing more than just sensing and moving; they are thinking as well. They are not just experiencing isolated sights and sounds but combining these experiences. In one study, for example, infants were shown two different videotapes at the same time, while the soundtrack for only one of them came from a speaker placed between the two TV screens. The infants tended to look at the video that went with the soundtrack—at a toy bouncing in synch with a tapping sound, at Dad’s face when his voice was on the audio, or at an angry face when an angry voice was heard (Soken & Pick, 1992). Infants remember, too. Babies as young as two to three months of age can recall a mobile that was hung over their crib a few days before (Rovee-Collier, 1999; see Figure 9.4). Young babies even seem to have a sense of object permanence. Piaget had required infants to demonstrate object permanence by making effortful responses, such as removing a cover that had been placed over an object. Today, researchers recognize that ﬁnding a hidden object under a cover requires several abilities: mentally representing the hidden object, ﬁguring out where it might be, and pulling off the cover. Piaget’s tests did not allow for the possibility that infants know a hidden object still exists but don’t yet have the skill to ﬁnd it. When researchers have created situations in which infants merely have to stare to indicate that they know where an object is hidden, even infants under the age of one have demonstrated this cognitive ability, especially when the object is a familiar one (Hespos & Baillargeon, 2001; Shinskey & Munakata, 2005). And when experimenters simply turn off the lights in a room, infants as young as ﬁve months of age may reach for now-unseen objects in the dark (Clifton et al., 1991). Developmental psychologists generally agree that infants develop some mental representations earlier than Piaget suggested. However, they disagree about whether this knowledge is “programmed” in infants (Spelke et al., 1992), whether it develops quickly through interactions with the world (Baillargeon, 1995), or whether it is constructed by combining old schemas into new ones (Fischer & Bidell, 1991). New Views of Infants’ Cognitive Development FIGURE 9 Infant Memory .4 This infant has learned to move a mobile by kicking her left foot, which is connected to the mobile by a ribbon. Even a month later, the baby will show recognition of this particular mobile by kicking more vigorously when she sees it than when she sees another one. T FOCUS ON RESEARCH o explore how infants develop mental representations, Renee Baillargeon (proWhat Do Infants Know nounced “by-ar-ZHAN”) investigated infants’ early understanding of the principles of About Physics? physics. Whether you realize it or not, you have quite a storehouse of knowledge about physics. You know about gravity and balance, for example. But when did you understand that “what goes up must come down” and that an unbalanced tray will tip over? Are these things you have always known, or did you ﬁgure them out through trial and error? ■ What was the researcher’s question? Baillargeon wanted to know when and how babies ﬁrst develop knowledge about balance and gravity—speciﬁcally, about the tendency of unsupported objects to fall. ■ How did the researcher answer the question? In one series of creative experiments, Baillargeon (1994a, 1994b, 2002) showed infants a red-gloved hand pushing a box from left to right along the top of a platform. On some trials, they saw physically possible events, as when the hand pushed the box to 353 Infancy and Childhood: Cognitive Development Source: Baillargeon (1992). (A) (B) (C) (D) FIGURE 9 .5 Events Demonstrating Infants’ Knowledge of Physics Infants look longer at things that interest them—that is, at new things rather than things they have seen before and ﬁnd boring. In her research on the development of knowledge, Renee Baillargeon (1995) has found that physically impossible events B and C—made possible by an experimenter’s reaching through a hidden door to support a moving box—attract the most attention from infants. These results suggest that humans understand some basic laws of physics quite early in life. the edge of the platform or held onto the object as it went beyond the edge of the platform (see events A and D in Figure 9.5). On other trials, they saw physically impossible events, as when the hand pushed the box until only the end of its bottom surface rested on the platform or went beyond the platform (see events B and C in the ﬁgure). Trials continued until the infants had seen at least four pairs of possible and impossible events in alternating order. Baillargeon measured the length of time the infants looked at the objects in each event. Their tendency to look longer at unexpected events provided an indication of which events violated what the babies knew about the world. ■ What did the researcher ﬁnd? Baillargeon found that three-month-old infants looked longest at impossible event C, in which the box was entirely off the platform. They were not particularly interested in either event D (box held by the gloved hand) or event A (box still on the platform). But at six and a half months, infants stared intently at both event C (box off the platform) and event B (in which only the end of the box was resting on the platform). ■ What do the results mean? According to Baillargeon (2002), these results suggest that three-month-old babies know something about physical support. They expected the box to fall if it was entirely off the platform and acted surprised when it did not. But they did not yet know that a box should fall if its center of gravity is unsupported, as in event B. By six and a half months of age, they had apparently developed this understanding. ■ What do we still need to know? Baillargeon may have demonstrated that very young infants possess fundamental knowledge about the world that implies an understanding of complex physical principles. But a question remains: Does an infant’s tendency to stare longer at a particular sight necessarily indicate “surprise,” or could it mean that babies simply recognize that certain images are different from, or more interesting than, things they have seen before (Bogartz, Shinskey, & Speaker, 1997)? The answer to this question will require further research using varied visual stimuli that allow researchers to determine whether infants stare longer at physically possible events that are just as novel and vivid as physically impossible events. Researchers also want to discover how babies know about physics (Johnson, Amso, & Slemmer, 2003). Does their knowledge develop from their experience with objects, 354 Chapter 9 Human Development © Bill Keane, Inc. Reprinted with special permission of King Features Syndicate. or is it innate? In an attempt to answer this question, Baillargeon conducted another experiment with infants ranging from three to six and a half months old. Half the children were randomly selected to receive extra experience watching objects falling when unsupported. After only a few demonstrations of such events, infants in the extraexperience group stared longer than the other babies when an unsupported object did not fall. Other studies found similar results (Needham & Baillargeon, 1999). It is still too early to say for sure whether Baillargeon’s hypothesis about the importance of experience in developing knowledge is correct, but her results seem to support it (Baillargeon, 2004; Wang & Baillargeon, 2005). So the next time you see an infant stacking blocks and watching them fall, consider the possibility that you are watching a little scientist testing hypotheses about the workings of the universe. During the second half of the preoperational period, according to Piaget, children believe that inanimate objects are alive and have intentions, feelings, and consciousness. preoperational period According to Piaget, the second stage of cognitive development, during which children begin to understand, create, and use symbols that represent things that are not present. conservation The ability to recognize that the important properties of a substance, such as number, volume, or weight, remain constant despite changes in shape, length, or position. Preoperational Development According to Piaget, the preoperational period follows the sensorimotor stage of development. During the ﬁrst half of this period, he observed, children begin to understand, create, and use symbols that represent things that are not present. They draw, pretend, and talk. Using and understanding symbols opens up a new world for two- to four-year-olds. At two, for the ﬁrst time, children are able to play “pretend.” They make their ﬁngers “walk” or “shoot” and use a spoon to make a bridge. By the age of three or four, children can symbolize complex roles and events as they play “house,” “doctor,” or “superhero.” They also can use drawing symbolically: Pointing to their scribble, they might say, “This is Mommy and Daddy and me going for a walk.” During the second half of the preoperational stage, according to Piaget, four- to seven-year-olds begin to make intuitive guesses about the world as they try to ﬁgure out how things work. However, Piaget observed that they cannot tell the difference between imagination and reality. For example, children in this age range might claim that dreams are real and take place outside of themselves as “pictures on the window,” “a circus in the room,” or “something from the sky.” And they believe that inanimate objects are alive and have intentions, feelings, and consciousness: “Clouds go slowly because they have no legs”; “Flowers grow because they want to”; and “Empty cars feel lonely.” Children in the preoperational period are also egocentric, meaning that they assume that their own view of the world is shared by everyone else. (This helps to explain why they stand between you and the TV screen and assume you can still see it, or ask “What’s this?” as they look at a picture book in the back seat of the car you’re driving.) Children’s thinking at this stage is so dominated by what they can see and touch for themselves that they do not realize something is the same if its appearance is changed. In one study, preoperational children thought that a cat wearing a dog mask was actually a dog, because that’s what it looked like (DeVries, 1969). These children do not yet have what Piaget called conservation, the ability to recognize that important properties of a substance or a person remain the same despite changes in shape or appearance. In a test of conservation, Piaget showed children water from each of two equal-sized glasses being poured into either a tall, thin glass or a short, wide one. They were then asked if one glass contained more water than the other. Children at the preoperational stage of development said that one glass (usually the taller one) contained more. They were dominated by the evidence of their eyes. If the glass looked bigger, then they thought it contained more. Children at this stage do not understand the logic of reversibility—that if you just poured the water from one container to another, you can pour it back, and it will be the same amount. Nor do they understand the concept of complementarity—that one glass is taller but narrower, and the other is shorter but wider. They focus on only one dimension at a time—the most obvious or important one—and make their best guess. In fact, Piaget named this stage preoperational because children at this stage do not yet understand logical mental operations such as reversibility and complementarity.