T H EM E S Nature and Nurture ❖ The Active Child ❖ Mechanisms of Change ❖ The Sociocultural Context ❖ ❚ concepts ❚ general ideas or understandings that can be used to group together objects, events, qualities, or abstractions that are similar in some way 260 S hawna, an 8-month-old, crawls into her 7-year-old brother’s bedroom. The room contains many objects: a bed, a dresser, a dog, a baseball, a baseball mitt, books, magazines, shoes, dirty socks, and so on. To her older brother, the room includes furniture, clothing, reading material, and sports equipment. But what does the room look like to Shawna? Infants lack concepts of furniture, reading material, and sports equipment, and also lack more specific, relevant concepts such as baseball mitts and books. Thus, Shawna would not understand the scene in the same way that her older brother would. However, without knowledge of child development research, it would be difficult to anticipate whether a baby as young as Shawna would have formed other concepts relevant to understanding the scene. Would she have formed concepts of living and nonliving things that would help her understand why the dog runs around on its own but the books never do? Would she have formed concepts of heavier and lighter that would allow her to understand why she could pick up a sock but not a dresser? Would she have formed concepts of before and after that would allow her to understand that her brother always puts on his socks before his shoes rather than in the opposite order? Or would it all be a jumble? As this imaginary scene indicates, concepts are crucial for helping people make sense of the world. But what exactly are concepts, and how do they help us understand? Concepts are general ideas that organize objects, events, qualities, or relations on the basis of some similarity. There are an infinite number of possible concepts, because there are infinite ways in which objects or events can be similar. For example, objects can have similar shapes (e.g., all football fields are rectangular), materials (e.g., all diamonds are made of compressed carbon), sizes (e.g., all giants are large), tastes (e.g., all candies are sweet), colors (e.g., all colas are brown), functions (e.g., all knives are for cutting), and so on. Concepts help us understand the world and act effectively in it by allowing us to generalize from prior experience. If we like the taste of one carrot, we probably will like the taste of others. Concepts also tell us how to react emotionally to new experiences, as when we fear all dogs after being bitten by one. Life without concepts would be unthinkable; every situation would be new, and we would have no idea what past experience was relevant in the new situation. As you will see in this chapter, several themes have been especially prominent in research on conceptual development. One is nature and nurture: children’s concepts reflect the interaction between their specific experiences and their biological predispositions to process information in particular ways. Another recurring theme is the active child: from infancy onward, many of children’s concepts reflect their active attempts to make sense of the world. A third major theme is how change occurs: researchers who study conceptual development attempt to understand not only what concepts children form but also the processes by which they form them. Although there is widespread agreement that conceptual development reflects the interaction of nature and nurture, the particulars of this interaction are hotly debated. The controversy parallels the nativist/empiricist controversies described previously in the context of perceptual development (page 182) and language development (pages 246–250). Nativists, such as Liz Spelke (Spelke & Kinzler, in press), Alan Leslie (Scholl & Leslie, 2002), and Karen Wynn (2007) believe that innate understanding of basic concepts plays a central role in development. They argue that infants are born with some sense of fundamental concepts such as time, space, causality, number, and the human mind, or with specialized learning mechanisms that allow them to acquire rudimentary understanding of these concepts unusually quickly and easily. Within the nativist perspective, nurture is important to children’s developing the concepts beyond this initial level, but not for forming the initial understanding. In contrast, empiricists, such as Scott Johnson (2010), Les Cohen (Cohen & Cashon, 2006), David Rakison (Rakison & Lupyan, 2008), and Marianella Casasola (2010) argue that nature endows infants with only general learning mechanisms, such as the ability to perceive, associate, generalize, and remember. Within the empiricist perspective, the rapid and universal formation of fundamental concepts such as time, space, causality, number, and mind arises from infants’ massive exposure to experiences that are relevant to these concepts. Empiricists also maintain that the data on which many nativist arguments are based—data involving infants’ looking times in habituationdishabituation studies—are not sufficient to support the nativists’ conclusions that infants understand the concepts in question (Campos et al., 2008; Kagan, 2008). The continuing debate between nativists and empiricists reflects a fundamental, unresolved question about human nature: Do children form all concepts through the same learning mechanisms, or do they also possess special mechanisms for forming a few particularly important concepts? The focus of this chapter is on the development of fundamental concepts, the ones that are useful in the greatest number of situations. These concepts fall into two groups. One group of fundamental concepts is used to categorize the kinds of things that exist in the world: people, living things in general, and inanimate objects. The other group of fundamental concepts are dimensions used to represent our experiences: space (where the experience occurred), time (when it occurred), causality (why it occurred), and number (how many times it occurred). You may have noticed that these fundamental concepts correspond closely to the questions that every news story must answer: Who or what? Where? When? Why? How many? The similarity between the concepts that are most fundamental for children and those that are most important in newspaper stories is no accident. Knowing who or what, where, when, why, and how many is essential for understanding any event. Because early conceptual development is so crucial, this chapter focuses on development in the first five years. This obviously does not mean that conceptual growth ends at age 5. Beyond this age, children form vast numbers of additional, more-specialized concepts, and understanding of all types of concepts deepens for many years thereafter. Rather, the focus on early conceptual development reflects the fact that this is the period in which children acquire a basic understanding of the most crucial concepts, the ones that are universal across societies, that allow children to understand their own and other people’s experiences, and that provide the foundations for subsequent conceptual growth. Understanding Who or What To even begin to understand the objects that they encounter, children must answer two key questions: What kinds of things are there in the world? And how are these things related to each other? Dividing the objects they encounter into categories helps children answer both questions. 261 KENNETH GARRETT / WOODFIN CAMP & ASSOCIATES UNDERSTANDING WHO OR WHAT What does this infant see when he looks at this room? 262 CHAPTER 7 CONCEPTUAL DEVELOPMENT Dividing Objects into Categories Beginning early in development, children attempt to understand what kinds of things there are in the world. They start by dividing the objects they perceive into the three most general categories shown at the top of Table 7.1: inanimate objects, people, and other living things (Wellman & Gelman, 1998). Forming these broad divisions is crucial, because different types of concepts apply to different types of objects (Keil, 1979). Some concepts apply to anything—all things, both living and nonliving, have heights, weights, colors, sizes, and so on. Other concepts apply only to living things—only living things eat, drink, grow, and breathe, for example. Yet other concepts—reading, shopping, pondering, and talking—apply to people. These distinctions among the three most general categories are important because they help children make accurate inferences about unfamiliar objects. When told that a platypus is a kind of animal, children know immediately that a platypus can move, eat, grow, reproduce, and so on. The importance of these distinctions also is evidenced by their being the subject of different academic fields: people are the focus of psychology, sociology, and anthropology (among other disciplines); plants and animals are the focus of biology, physiology, and anatomy; and objects are the focus of physics, computer science, and engineering. The columns within Table 7.1 illustrate a major means by which categorization helps children solve the question of how things in the world are related to each other. Children form category hierarchies, that is, categories related by set–subset relations. The furniture/chair/La-Z-Boy example shown in the table is one example. The category “furniture” includes all chairs; the category “chair” includes all La-Z-Boys. Forming such category hierarchies greatly simplifies the world for children by allowing them to draw accurate inferences. If children are told that a La-Z-Boy is a kind of chair, they can use their general knowledge of chairs to infer that people sit on La-Z-Boys and that La-Z-Boys are neither lazy nor boys. Of course, infants are not born knowing about La-Z-Boys and chairs, nor are they born knowledgeable about the other categories shown in Table 7.1. Thus, one important question is: How do children form categories that apply to all kinds of objects, living and nonliving? Categorization of Objects in Infancy Even in the first months of life, infants form categories of objects. Quinn and Eimas (1996), for example, found that as 3- and 4-month-olds were shown a series TABLE 7.1 Object Hierarchies Level Type of Object Most General Inanimate Objects People Living Things General Furniture, Vehicles . . . Europeans, Asians . . . Animals, Plants . . . Medium Chairs, Tables . . . Spaniards, Finns . . . Cats, Dogs . . . Specific La-Z-Boys, Armchairs . . . Picasso, Cervantes . . . Lions, Lynxes . . . ❚ category hierarchy ❚ categories that are related by set–subset relations, such as animal/dog/poodle 263 UNDERSTANDING WHO OR WHAT CRESZENTIA AND TED ALLEN GUIDE TO CATS, GINO PUGNETTI © 1983 BY ARNOLDO MONDADORI S.P.A. MILANO KARL WOLFFRAM JAL DUNCAN HERVE CHANMETON CHAMALIERS CRESZENTIA AND TED ALLEN CRESZENTIA AND TED ALLEN ❚ perceptual categorization ❚ the grouping together of objects with similar appearances MARC HENRIE ASC, LONDON of photographs of different cats, they habituated; that is, they looked at new cat photographs for less and less time (Figure 7.1). However, when the infants were subsequently shown a picture of a dog, lion, or other animal, they dishabituated; that is, their looking time increased. Their habituation to the cat photographs suggests that the infants saw all the cats, despite their differences, as members of a single category; their subsequent dishabituation to the photo of the dog or other animal suggests that the infants saw those creatures as members of different categories than the cats. Moreover, 6-month-olds displayed similar brain activity when shown sets of pictures of both familiar and unfamiliar cats, whereas their brain activity in response to pictures of unfamiliar dogs differed from that to both sets of cats (Quinn, Westerlund, & Nelson, 2006). Infants also can form categories more general than “cats.” Behl-Chadha (1996) found that 6-month-olds habituated after repeatedly being shown pictures of different types of mammals (dogs, zebras, elephants, etc.) and then dishabituated when they were shown a picture of a bird or a fish. The infants apparently perceived similarities among the mammals that led to their eventually losing interest in them. The infants also apparently perceived differences between the mammals and the bird or fish that led them to show renewed interest. As suggested by this example, a key element in infants’ categorization abilities is perceptual categorization, the grouping together of objects that have similar appearances (Cohen & Cashon, 2006; Madole & Oakes, 1999). Prior to participating in the Behl-Chadha (1996) study, few infants, if any, would have had experience with zebras or elephants. Thus, the distinctions the infants made between these mammals and the birds and fish could only have been based on a perception of the animals’ differing appearances. Infants categorize objects along many perceptual dimensions, including color, size, and movement. Often their categorization is largely based on specific parts of an object rather than on the object as a whole; for example, infants younger than 18 months of age rely heavily on the presence of legs to categorize objects as animals, and they rely heavily on the presence of wheels to categorize objects as vehicles (Rakison & Lupyan, 2008; Rakison & Poulin-Dubois, 2001). FIGURE 7.1 Infant categorization These photos were used by Quinn and Eimas (1996) to study infant categorization. In their experiment, 3- and 4-month-olds were repeatedly shown photos of pairs of cats that looked quite different from each other (Trials 1–3). After the infants habituated to the cat photos, presentation of a photo of a cat and another animal (Trial 4) led them to look longer at the other animal. Thus, despite lacking knowledge of cats and other animals, infants form categories that allow them to discriminate between members of the category and members of related but different categories. 264 CHAPTER 7 CONCEPTUAL DEVELOPMENT As children approach their 2nd birthday, they increasingly categorize objects on the basis of overall shape. As discussed in Chapter 6, when toddlers are shown an unfamiliar object and told that it is a “dax,” they assume that other objects of the same shape are also “daxes,” even when the objects differ from each other in size, texture, and color (Landau, Smith, & Jones, 1998). This is a useful assumption, because for many objects, shape indeed is similar for different members of a category. If we see a silhouette of a cat, hammer, or chair, we can tell from the shape what the object is. However, we rarely can do the same if we know only the object’s color or size or texture. By the end of their first year, infants also form categories on the basis of objects’ functions. This capability was evident in a study in which 9- and 10-month-olds were shown castanets that produced clacking sounds when they were squeezed (Baldwin, Markman, & Mellartin, 1993). When the babies were later given a similar-looking toy, they squeezed it in an apparent effort to reproduce the sound. If the similar-looking toy did not make the sound, the infants persisted in squeezing it. (If the toy they were given did not resemble the original, they didn’t squeeze it.) They apparently expected that a toy that looked like the original would serve the same function, in this case making the same interesting noise. Categorization of Objects Beyond Infancy As children move beyond infancy, they increasingly grasp not only individual categories but also hierarchical and causal relations among categories. ❚ superordinate level ❚ the most general level within a category hierarchy, such as “animal” in the animal/dog/poodle example ❚ subordinate level ❚ the most specific level within a category hierarchy, such as “poodle” in the animal/dog/poodle example ❚ basic level ❚ the middle level, and often the first level learned, within a category hierarchy, such as “dog” in the animal/dog/poodle example Category hierarchies The category hierarchies that young children form often include three of the main levels in Table 7.1: the general one, which is called the superordinate level; the very specific one, called the subordinate level; and the medium or in-between one, called the basic level (Rosch, Mervis, et al., 1976). As its name suggests, the basic level is the one that children usually learn first. Thus, they typically form categories of medium generality, such as “tree,” before they form more general categories such as “plant” or more specific ones such as “oak.” The reasons why children generally form the basic level first are not hard to understand. A basic-level category such as “tree” has a number of consistent characteristics: bark, branches, large size, and so on. In contrast, the more general category “plant” has fewer consistent characteristics: plants come in a wide range of shapes, sizes, and colors (consider an oak, a rose, and grass). Subordinate-level categories have the same consistent characteristics as the basic-level category, and some additional ones—all oaks, but not all trees, have rough bark and pointed leaves, for example. However, it is relatively difficult to discriminate among different subordinate categories within the same basic-level category (oaks versus maples, for example). Thus, it is not surprising that children tend to form basic-level categories first. It should be noted that very young children’s basic categories do not always match those of adults. For example, rather than forming separate categories of cars, motorcycles, and buses, young children seem to group these objects together into a category of “objects with wheels” (Mandler & McDonough, 1998). Even in such cases, however, the initial categories are less general than such categories as “moving things” and more general than ones such as “Toyotas.” Having formed basic-level categories, how do children go on to form superordinate and subordinate categories? Part of the answer is that parents and others use the child’s basic-level categories as a foundation for explaining the more specific 265 UNDERSTANDING WHO OR WHAT and more general categories (Gelman, Coley, Rosengren, Hartman, & Pappas, 1998). When parents teach children superordinate categories such as mammals, they typically illustrate the relevant terms with basic-level examples that the child already knows (Callanan, 1990). They might say, “Mammals are animals, like foxes, bears, and cows, that get milk from their mothers when they are babies.” Parents also refer to basic-level categories to teach children subordinate-level terms (Callanan & Sabbagh, 2004; Waxman & Senghas, 1992). For example, they might say “A beluga is a kind of whale.” Such descriptions allow children to use what they already know about basic-level categories to form superordinate- and subordinate-level categories. The example also illustrates the importance of the social world in explaining how change occurs in conceptual development. Although parents’ explanations clearly enhance children’s conceptual understanding, the learning path sometimes involves amusing detours. In one such case, Susan Gelman (2003) gave her 2-year-old son a spoon and a container filled with bite-size pieces of fruit and said “This is a fruit cup.” The boy responded to her description by picking up the “cup” and attempting to drink from it. Children’s active attempts to understand their experiences lead to many short-lived but interesting concepts such as the “fruit cup.” Causal understanding and categorization Toddlers and preschoolers are notorious for their endless questions about causes and reasons. “Why do dogs bark?” “How does the telephone know where to call?” “Where does rain come from?” Although parents are often exasperated by such questions, their respecting and answering them helps children learn. Understanding causal relations is crucial in forming many categories. How could children form the category of “light switches,” for example, if they did not understand that flipping light switches causes lights to go on and off? To study how an understanding of causes influences category formation, Krascum and Andrews (1998) told 4- and 5-year-olds about two categories of imaginary animals: wugs and gillies. Some of the preschoolers were provided only physical descriptions of the animals: they were told that wugs usually have claws on their feet, spikes on the end of their tails, horns on their heads, and armor on their backs; gillies were described as usually having wings, big ears, long tails, and long toes. Other children were provided the same physical descriptions, plus a simple causal story that explained why wugs and gillies are the way they are. These children were told that wugs have claws, spikes, horns, and armor because they like to fight. Gillies, in contrast, do not like to fight; instead, they hide in trees. Their big ears let them hear approaching wugs, their wings let them fly away to treetops, and so on. After the children in both groups were given the information about these animals, they were shown the pictures in Figure 7.2 and asked which animal was a wug and which was a gilly. The children who were told why wugs and gillies have the physical features they do were better at classifying the pictures into the appropriate categories. When tested the next day, those children also remembered the categories better than did the children who were given the physical descriptions without explanations. Thus, understanding cause–effect relations helps children learn and remember new categories. Preschoolers’ questions about causes and reasons show that they understand that different categories of objects, such as artifacts and animals, vary in the types of causal relations in which they are typically involved. Artifacts (objects made by “Wug” “Gilly” FIGURE 7.2 Cause–effect relations Hearing that wugs are well prepared to fight and gillies to flee helped preschoolers categorize novel pictures like these as wugs or gillies (Krascum & Andrews, 1998). In general, understanding cause– effect relations helps people of all ages learn and remember. 266 CHAPTER 7 CONCEPTUAL DEVELOPMENT people) usually are designed for specific purposes: forks are for eating food, cups are for drinking liquids, pens are for writing, and so on. In contrast, animals are not made for any human purpose (although people often put them to some specific use). The questions that 3- and 4-year-olds typically ask about artifacts and animals show that they understand these categorical differences. Their questions about novel artifacts, for example, focus on the goals that artifacts enable people to pursue (e.g., “What is this for?”). In contrast, preschoolers’ questions about animals focus on the animals’ own goals (“What do they like to eat?”) (Greif, KemlerNelson, Keil, & Guitierrez, 2006; Kemler-Nelson, Egan, & Holt, 2004). Knowledge of Other People and Oneself Although understanding of oneself and others varies greatly from individual to individual, there is a commonsense level of psychological understanding that just about everybody has. As discussed in Chapter 4 (page 157), this understanding, referred to as naïve psychology, is crucial to normal human functioning. At the center of naïve psychology are two concepts that we all normally use to understand human behavior: desires and beliefs. We apply these concepts almost every time we think about why someone did something. For example, why did Jimmy go to Billy’s house? He wanted to play with Billy (a desire), and he expected that Billy would be at home (a belief ). Why did Jenny turn on the TV at 8:00 A.M. on Saturday? She was interested in watching “SpongeBob” (a desire), and she thought the program was on at that time (a belief ). Three properties of naïve psychological concepts are noteworthy. First, they refer to invisible mental states. No one can see a desire, a belief, a perception, a memory, or the like. We, of course, can see behaviors related to psychological concepts, such as Jimmy’s ringing Billy’s doorbell, but we can only infer the underlying mental state, such as Jimmy’s desire to see Billy. Second, the concepts are all linked to each other in cause–effect relations. Jimmy, for example, might get angry if Billy isn’t home because he went to a different friend’s house, which could later cause Jimmy to be mean to his younger brother. The third noteworthy property of these naïve psychological concepts is that, as we will presently see, they develop early in life. Sharp disagreements have arisen between nativists and empiricists regarding the source of this early psychological understanding. Nativists (e.g., Leslie, 2000) argue that the early understanding is possible only because children are born with an innate basic understanding of human psychology. In contrast, empiricists (e.g., Frye, Zelazo, Brooks, & Samuels, 1996; Ruffman, Slade, & Crowe, 2002) argue that experiences with other people and general information-processing capacities are the key sources of the early understanding of other people. There is evidence to support each of these views. Infants’ Naïve Psychology ❚ naïve psychology ❚ a commonsense level of understanding of other people and oneself As we saw in Chapter 5, infants find people interesting, pay careful attention to them, and learn an impressive amount about them in the first year. Even very young infants prefer to look at people’s faces rather than at other objects. Infants also imitate people’s facial movements, such as sticking out one’s tongue, but they do not imitate the motions of inanimate objects. And it is not just the face that interests infants; they also prefer to watch human bodies moving instead of other displays with equal amounts of movement (Bertenthal, 1993). This early interest in human faces and bodies helps infants learn about people’s behavior. Imitating other people and forming emotional bonds with them encourages UNDERSTANDING WHO OR WHAT 267 the other people to interact more with the infants, creating additional opportunities for the infants to acquire psychological understanding. As noted in earlier discussions, many important aspects of psychological understanding emerge late in the first year and early in the second. One is an understanding of intention, the desire to act in a certain way. Other key psychological concepts that emerge at the same time include joint attention, in which two or more people focus intentionally on the same referent; and intersubjectivity, the mutual understanding that people share during communication (pages 161–162). One-year-olds’ understanding of other people includes an understanding of their emotions. Consider the following incident: Michael, 15 months, is struggling with his friend Paul over a toy. Paul starts to cry. Michael appears concerned and lets go of the toy, so Paul has it. Paul continues crying. Michael pauses, then gives his own teddy bear to Paul; Paul continues crying. Michael pauses again, runs to the next room, gets Paul’s security blanket, and gives it to him. Paul stops crying. (Hoffman, 1976, pp. 129–130) Although interpreting anecdotes is always tricky, it seems likely that Michael understood that giving Paul something desirable might make him feel better (or at least stop his crying). Michael’s leaving the room, getting Paul’s security blanket, and bringing it back to him suggests that Michael had the further insight that Paul’s blanket might be especially useful for soothing his hurt feelings. This interpretation is consistent with a variety of evidence suggesting that 1-year-olds fairly often offer both physical comfort (hugs, kisses, pats) and comforting comments (“You be OK”) to unhappy playmates. Presumably, infants’ experience of their own emotions and the behaviors that accompany them helps them understand others’ emotions when they act similarly (Harris, 2006). Development Beyond Infancy In the toddler and preschool periods, children build on their early-emerging psychological understanding to develop an increasingly sophisticated comprehension of themselves and other people and to interact with others in increasingly complex ways. Two areas of especially impressive development are children’s understanding of other people’s minds and their play with peers. The growth of a theory of mind Infants’ and preschoolers’ naïve psychology, together with their strong interest in other people, provides the foundation for the development of a theory of mind, an organized, integrated understanding of how psychological processes such as intentions, desires, beliefs, perceptions, and emotions influence behavior. Preschoolers’ theory of mind includes, for example, knowledge that beliefs often originate in perceptions, such as seeing an event or hearing someone describe it; that desires can originate either from physiological states, such as hunger or pain, or from psychological states, such as wanting to see a friend; and that desires and beliefs produce actions (Wellman & Gelman, 1998). One important component of such a theory of mind—understanding the connection between other people’s desires and their actions—emerges by the end of the first year. In a study by Phillips, Wellman, and Spelke (2002), 12-month-olds saw an experimenter look at one of two stuffed kittens and say in a joyful voice, “Ooh, look at the kitty!” Then a screen descended, and when it was raised 2 seconds later, the experimenter was holding either the kitty that she had just exclaimed over or the ❚ theory of mind ❚ a basic understanding of how the mind works and how it influences behavior 268 CHAPTER 7 What do you think is in the box? “Smarties!” Why don’t you open the box and see? Oh, it’s pencils. SM AR TI ES Let’s close the box. What do you think your friend Jenny would say is in the box if she saw it? Pencils! RTIE S SMA FIGURE 7.3 Testing children’s theory of mind The Smarties task is frequently used to study preschoolers’ understanding of false beliefs. Most 3-year-olds answer the way the child in this cartoon does, which suggests a lack of understanding that people’s actions are based on their own beliefs, even when those beliefs deviate from what the child knows to be true. CONCEPTUAL DEVELOPMENT other one. The 12-month-olds looked longer when the experimenter was holding the other kitty, suggesting that they expected the experimenter to want to hold the kitty that had just excited her so much and were surprised that she was holding the other one. Eight-month-olds look for similar amounts of time regardless of which kitty the experimenter is holding, suggesting that the understanding that people’s desires guide their actions develops toward the end of the first year (Phillips et al., 2002). Consistent with this conclusion, 10-month-olds can use information about a person’s earlier desires to predict that person’s later desires, but only under virtually identical circumstances (Sommerville & Crane, 2009). Children’s understanding that desires lead to actions is firmly established by age 2 years. Children of this age, for example, predict that characters in stories will act in accord with their own desires, even when those desires differ from the child’s wishes (Gopnik & Slaughter, 1991; Lillard & Flavell, 1992). Thus, if 2-year-olds who would rather play with trucks than with dolls are told that a character in a story would rather play with dolls than with trucks, they predict that, given the choice, the character in the story will choose dolls over trucks. Although most 2-year-olds understand that desires can influence behavior, they show little understanding that beliefs are likewise influential. Thus, when 2-yearolds were told a story in which a character named Sam believed that the only bananas available were in a cupboard, but they themselves knew that there were bananas in a refrigerator as well, they were no more likely than chance to predict that Sam would act in accord with his own belief and search for bananas only in the cupboard (Wellman & Woolley, 1990). By age 3 years, children show some understanding of the relation between beliefs and actions. For example, they answer questions such as “Why is Billy looking for his dog?” by referring to beliefs (“He thinks the dog ran away”) as well as to desires (“He wants it”) (Bartsch & Wellman, 1995). Most 3-year-olds also have some knowledge of how beliefs originate. They know, for example, that seeing an event produces beliefs about it, whereas simply being next to someone who can see the event does not (Pillow, 1988). At the same time, 3-year-olds’ understanding of the relation between people’s beliefs and their actions, a key part of their theory of mind, is limited in important ways. These limitations are evident when children are presented with false-belief problems, in which another person believes something to be true that the child knows is false. The question is whether the child thinks that the other person will act in accord with his or her own false belief or in accord with the child’s correct understanding of the situation. Studying such situations reveals whether children understand that other people’s actions are determined by the contents of their own minds, rather than the objective truth of the situation or the child’s understanding of it. In one false-belief problem, preschoolers are shown a box that ordinarily contains a type of candy called Smarties and that has a picture of the candy on it (Figure 7.3). The experimenter then asks what is inside the box. Logically enough, the preschoolers say “Smarties.” Next, the experimenter opens the box, revealing that it actually contains pencils. Most 5-year-olds laugh or smile and admit their surprise. When asked what another child would say if shown the closed box and asked to guess its contents, they say the child would answer “Smarties,” just as they had. Not 3-year-olds! A large majority claim they always knew what was in the box, and they predict that if some other child were shown the box, that child would also believe that the box contained pencils (Gopnik & Astington, 1988). The 3-yearolds’ responses show they have difficulty understanding that other people act on their own beliefs, even when those beliefs are false. This finding is extremely robust. A review of 178 studies of children’s understanding of false beliefs showed that similar results emerged with different forms of the problem, different questions, and different societies (Wellman, Cross, & Watson, 2001). In one noteworthy cross-cultural study, false-belief problems were presented to children attending preschools in Canada, India, Peru, Thailand, and Samoa (Callaghan et al., 2005). Performance improved greatly between ages 3 and 5 years in all five societies, from 14% correct for 3-year-olds to 85% correct for 5-year-olds. Especially striking was the consistency of performance across these very different societies: in no country did 3-year-olds answer more than 25% of problems correctly, and in no country did 5-year-olds answer less than 72% correctly. Although 3-year-olds generally err on false-belief problems when the problems are presented in the standard way, many children of this age succeed if the task is presented in a manner that facilitates understanding. For example, if an experimenter tells a 3-year-old that the two of them are going to play a trick on another child by hiding pencils in a Smarties box and enlists the child’s help in filling the box with pencils, most 3-year-olds correctly predict that the other child will say that the box contains Smarties (Sullivan & Winner, 1993). Presumably, assuming the role of deceiver and hiding the pencils in the candy box helps 3-year-olds see the situation from the other child’s perspective. Nonetheless, it is striking just how difficult 3-year-olds find standard false-belief problems. To date, no set of conditions has enabled 3-year-olds to solve standard false-belief questions correctly more often than chance (Harris, 2006). Explaining the development of theory of mind People’s lives clearly would be very different without a reasonably sophisticated theory of mind. However, the findings on the improvement in normal children’s theory of mind between ages 3 and 5 do not tell us what causes the improvement. This question has generated enormous controversy, and currently there is great disagreement about how to answer it. Investigators who take a nativist position have proposed the existence of a theory of mind module (TOMM), a hypothesized brain mechanism devoted to understanding other human beings (Baron-Cohen, 1995; Leslie, 2000). Adherents of this position argue that among typical children exposed to a typical environment, the TOMM matures over the first five years, producing an increasingly sophisticated understanding of people’s minds. These investigators cite evidence from brain-imaging studies showing that certain areas of the brain are consistently active in representing beliefs across different tasks, and that the areas are different from those involved in other complex cognitive processes, such as understanding grammar (Saxe & Powell, 2006). Further evidence that is often cited to support the idea of the TOMM comes from children with autism. As discussed in Box 7.1 on the next page, these children have great difficulty with false-belief problems, a difficulty that appears closely associated with a wide array of limitations in their social interactions. Especially significant to the idea of the TOMM is the discovery that individuals with autism appear to be missing a significant band of tissue in the brain stem (Rodier, 2000). The problem originates in the first month of the prenatal period 269 SUPERSTOCK UNDERSTANDING WHO OR WHAT Despite leading very different lives, pygmy children in Africa and same-age peers in industrialized North American and European societies respond to the false-belief task in the same way. ❚ false-belief problems ❚ tasks that test a child’s understanding that other people will act in accord with their own beliefs even when the child knows that those beliefs are incorrect ❚ theory of mind module (TOMM) ❚ a hypothesized brain mechanism devoted to understanding other human beings 270 CHAPTER 7 CONCEPTUAL DEVELOPMENT 7.1 individual differences Children with Autism Although most children readily handle false-belief problems by the age of 5 years, one group continues to find them very difficult even when they are teenagers: children with autism. As discussed in Chapter 3 (page 93), this syndrome, which strikes roughly 1 in 600 children in the United States, most of them male (Rodier, 2000), involves difficulties in social interaction, communication, and other intellectual and emotional functions. Autistic children often engage in solitary repetitive behaviors, such as continually rocking back and forth or endlessly skipping around a room. They interact minimally with other children and adults, rarely form close relationships, and tend to be more interested in objects than in people. These problems, among others, have led some researchers to speculate that a failure to understand other people underlies autistic children’s limited involvement in the social world. Recent research supports this hypothesis. Children with autism have trouble establishing joint attention with other people; in fact, there is little evidence that they ever do so (Klin et al., 2004). Compared with both typical children and children with mental retardation, autistic children show less concern when other people appear distressed (Sigman & Ruskin, 1999) or experience circumstances that would lead most people to be distressed (Hobson, Harris GarcíaPeréz, & Hobson, 2009). Autistic children also tend to have poor language skills (Happé, 1995), which both reflects their lack of attention to other people and limits their opportunities to learn about people’s thoughts and feelings through conversation. In line with these patterns, autistic children are strikingly befuddled by falsebelief questions (Baron-Cohen, 1991). For example, fewer than half of 6- to 14year-olds with autism solve false-belief problems that are easy for typical 4- and 5-year-olds (Peterson, Wellman, & Liu, 2005). Autistic children have some understanding of how desire affects behavior, but the ways in which beliefs influence behavior largely eludes them (Harris, 2006; Tager-Flusberg, 2007). Other groups with limited language skills, such as deaf children who learn to sign relatively late, also show delays in mastering false-belief tasks. However, autistic children differ both from these deaf children and from preschoolers in that they understand false beliefs later than other aspects of psychology that are typically understood after false beliefs (Peterson, Wellman, & Liu, 2005). Impaired theory-of-mind mechanisms are not the only source of the difficulty that children with autism encounter in understanding other people. More general deficits in planning, adapting to changing situations, and controlling working memory also contribute (Ozonoff et al., 2004). Nonetheless, impaired theory of mind is a source of particular difficulty, especially in understanding situations in which people’s beliefs differ from reality (BaronCohen, 1993; Tager-Flusberg, 2007). Identifying the difficulty that children with autism have in understanding other people’s minds as a major source of the problems encountered in autism may contribute to the development of more effective treatments for this strange and baffling condition. An autistic child, sitting in his mother’s lap, shows a distinct lack of interest in her affection. Such lack of interest in other people is common among autistic children and seems related to their very poor performance on tasks that require understanding of other people’s minds. JAN SONNENMAIR / AURORA and may be related to other abnormalities in later developing parts of the brains of autistic children. One area that is typically affected is the amygdala, which plays a crucial role in experiencing and understanding emotions; another is the hippocampus, which plays a crucial role in memory. All these parts of the brain are important for a variety of functions, but abnormalities in them may be especially detrimental to understanding other people. A different explanation of the development of theory of mind is suggested by theorists who take an empiricist stance and maintain that psychological understanding arises from interactions with other people ( Jenkins & Astington, 1996; Ruffman, Slade, & Crowe, 2002). They cite evidence that on false-belief tasks, preschoolers who have siblings outperform peers who do not. This finding appears to be especially likely when the siblings are older or of the opposite sex, presumably because interacting with people whose interests, desires, and motives are different from their own broadens children’s understanding of the mind (Cassidy et al., 2005; Jenkins & Astington, 1996). From this perspective, the tendency of children with autism not to interact with other people is a major contributor to the children’s difficulty in understanding people. A third group of investigators also takes an empiricist stance but emphasizes the growth of general information-processing skills as essential to children’s understanding of other people’s minds. They cite evidence that understanding false-belief problems is substantially correlated with the ability to reason about complex counterfactual statements (German & Nichols, 2003) and with the ability to inhibit one’s own relatively automatic behavioral reactions (Carlson, Mandell, & Williams, 2004; Frye, Zelazo, Brooks, & Samuels, 1996). The ability to reason about counterfactual statements is important because false-belief problems require children to predict what a person would do on the basis of a counterfactual belief. The ability to inhibit relatively automatic reactions is important because false-belief problems also require children to suppress the assumption that the person would act on the truth of the situation. Investigators in this camp argue that typical children under age 4 and children with autism lack the information-processing skills needed to understand others’ minds, whereas many typical 4-year-olds and almost all typical 5-year-olds can engage in such processing. All three explanations seem to have merit. Normal development of brain regions relevant to understanding other people, increasing experience with other people, and improved information-processing capacity all contribute to the growth of psychological understanding during the preschool years. Together, they allow almost all children to achieve a basic, but useful, theory of mind by age 5. The growth of play Play refers to activities that are pursued for their own sake, without any motivation other than the enjoyment they bring. The earliest play activities, such as banging a spoon on a high-chair tray, tend to be solitary. However, over the next few years, children’s increasing understanding of other people contributes to their play becoming more social, as well as more complex. One early milestone in the development of play is the emergence of pretend play at around 18 months of age. When engaged in pretend play, children act as if they were in a different situation than their actual one. They often engage in object substitution, ignoring many of a play object’s characteristics so that they can pretend that it is something else. A typical example of such object substitution 271 COURTESY OF ALICE AND ROBERT SIEGLER UNDERSTANDING WHO OR WHAT Sharing experiences with older siblings helps younger siblings understand other people. ❚ pretend play ❚ make-believe activities in which children create new symbolic relations, for example, using a broom to represent a horse ❚ object substitution ❚ a form of pretense in which an object is used as something other than itself MICHAEL NEWMAN / PHOTOEDIT 272 Sociodramatic play, in which children create minidramas based on their experiences, both reflects children’s understanding of the situation and helps them increase that understanding. LAURA DWIGHT Children often enjoy having a parent join them in sociodramatic play, which tends to be richer and more informative when the parent provides scaffolding for the play episode. Along with helping to structure the tea-time conversation, the mother in this classic scenario may also be providing her daughter with tips on party etiquette. CHAPTER 7 CONCEPTUAL DEVELOPMENT would be a child’s cradling a pillow and talking to it as if it were a baby, or talking to a doll as if it were a friend. About a year later, toddlers begin to engage in sociodramatic play, a kind of pretend play in which they enact miniature dramas with other children or adults, such as “mother comforting baby” or “doctor helping sick child” (O’Reilly & Bornstein, 1993). Sociodramatic play is more complex and more social than object substitution. Consider, for example, “tea party” rituals, in which a child and parent “pour tea” for each other from an imaginary teapot, daintily “sip” it, “eat” imaginary cookies, and comment on how delicious they are. Young children’s sociodramatic play is typically more sophisticated when they are playing with a parent or older sibling who can scaffold the play sequence than when they are pretending with a peer (Bornstein, 2006; Lillard, 2006). Such scaffolding during play provides children with opportunities for learning, in particular for improving their storytelling skills (Nicolopoulou, 2006). Consider one mother’s comments as her 2-yearold played with two action figures: Oh look, Lantern Man is chasing Spider Man. Oh no, he is pushing him down. Spider Man says, ‘Help, Lantern Man is grabbing me.’ Look, Spider Man is getting away. (Kavanaugh & Engel, 1998, p. 88) Such adult elaboration of implicit storylines in children’s play provides a useful model for children to follow as they become more verbal. By the elementary school years, play becomes even more complex and social. It begins to include activities, such as sports and board games, that have conventional rules that participants must follow. The frequent quarrels that arise among young elementary school students regarding who is obeying the rules and playing fair attest to the cognitive and emotional challenges posed by these games (Rubin, Fein, & Vandenberg, 1983). The quantity of young children’s pretend play is related to their understanding of other people’s psychological functioning. Children who engage in greater amounts of pretend play tend to show greater understanding of other people’s thinking (Lillard, 2006) and emotions (Youngblade & Dunn, 1995). The type of pretend play in which children engage also matters: social pretend play is more strongly related to understanding other people’s thinking than is nonsocial pretend play (Harris, 2000). Pretend play may lead toddlers and preschoolers to consider how various situations would make them or their play partner think and feel, and in this way it may increase their understanding of other people. Consistent with this conclusion, children who participate in greater-than-average amounts of pretend play with other children also tend to be popular with their peers and socially mature, perhaps because such play enhances their understanding of other children’s feelings (Howes & Matheson, 1992). Thus, although adults often view children’s pretend play as unimportant, it is positively related to children’s social and intellectual development and may even enhance them. 273 UNDERSTANDING WHO OR WHAT Knowledge of Living Things Children find living things fascinating, especially animals. One sign of their fascination is how often their first words refer to animals. In a study of the first 50 words used by children, the two terms that were used by the greatest number of children were “dog” and “cat” (and variants such as “doggie” and “kitty”) (Nelson, 1973). “Duck,” “horse,” “bear,” “bird,” and “cow” also were among the most common early terms. By the time children are 4 or 5 years old, their fascination with living things translates into an impressive amount of knowledge about them, including knowledge of unobservable biological processes such as inheritance, illness, and healing. 7.2 Imaginary Companions failed to leave when no longer welcome (Taylor & Mannering, 2007). In this independence from their creator, the imaginary companions resemble characters invented by novelists, who often report that their characters at times seem to act independently, including making statements the authors did not intend and arguing with and criticizing them (Taylor & Mannering, 2007). Contrary to popular speculation, Taylor (1999) found that, in terms of broad characteristics such as personality, intelligence, and creativity, children who invent imaginary playmates are no different from children who do not. However, she and other investigators have identified a few, relatively specific differences between these two groups. Children who had created imaginary playmates were more likely (1) to be firstborn or only children; (2) to watch relatively little television; (3) to be verbally skillful; and (4) to have advanced theories of mind (Carlson, Gum, Davis, & Malloy, 2003; Taylor & Carlson, 1997; Taylor et al., 2004). These rela- Although the sight of their child feeding someone who isn’t there might worry some parents, the majority of children enjoy the company of imaginary friends at some time in early childhood. tions make sense. Being without siblings may motivate some firstborn and only children to invent friends to keep them company; not watching much television frees time for imaginative play; and being verbally skilled and having an advanced theory of mind may enable children to imagine especially interesting companions and especially interesting adventures with them. Companionship, entertainment, and enjoyment of fantasy are not the only reasons why children invent imaginary companions. Children also use them to deflect blame (“I didn’t do it; Blebbi Ussi did”), to vent anger (“I hate you, Blebbi Ussi”), and to convey information that the child is reluctant to state directly (“Blebbi Ussi is scared of falling into the potty”). As Taylor (1999) noted, “Imaginary companions love you when you feel rejected by others, listen when you need to talk to someone, and can be trusted not to repeat what you say” (p. 63). It is no wonder, then, that so many children invent them. SHERRY WHITMORE individual differences Many children have an imaginary companion whom they appear to regard as an actual being. Marjorie Taylor (1999) found that 63% of children whom she interviewed at age 3 or 4 years and again at age 7 or 8 years reported having imaginary companions at one or both times. In another study, Taylor and colleagues (2004) found that as many 6- and 7-yearolds as 3- and 4-year-olds said that they had imaginary companions—31% of older children and 28% of younger ones. Hearing a child talk about an invisible friend sometimes leads parents to worry about their child’s mental health, but as these statistics show, children’s creation of such companions is entirely normal. Most of the imaginary playmates described by children in Taylor’s studies were ordinary boys and girls who happened to be invisible, but others were more colorful. They included Derek, a 91-year-old man who was said to be only 2 feet tall but able to hit bears; “The Girl,” a 4-year-old who always wore pink and was “a beautiful person”; Joshua, a possum who lived in San Francisco; and Nobby, a 160-year-old businessman. Other imaginary companions were modeled after specific people: two examples were MacKenzie, an imaginary playmate who resembled the child’s cousin MacKenzie, and “Fake Rachel,” who resembled the child’s friend Rachel. As with real friends, children have a variety of complaints about their imaginary companions. In a study of 36 preschoolers with imaginary companions, only one child had no complaints; the other 35 children griped that their imaginary companions argued with them, refused to share, failed to come when invited, and ❚ sociodramatic play ❚ activities in which children enact minidramas with other children or adults, such as “mother comforting baby” COURTESY OF SUWANNA AND DAVID SIEGLER 274 Children are interested in living things, plants as well as animals—especially when part of the plant tastes good. CHAPTER 7 CONCEPTUAL DEVELOPMENT Coexisting with this relatively advanced knowledge, however, are a variety of immature beliefs and types of reasoning. For example, despite the previously mentioned differences in the questions preschoolers ask about animals and artifacts (Kemler-Nelson & Greif, 2006), when preschoolers and older children are asked certain types of “why” questions, the distinction blurs. For example, when Kelemen and DiYanni (2005) asked 6- to 10-year-olds why the first monkey came to exist, they often advanced answers such as “The manager of the zoo-place wanted some” and “So then we had somebody to climb trees.” Children advance similar answers to questions about the possible purposes of inanimate natural entities, such as rocks. When 7- and 8-year-olds were asked whether rocks were pointy “because bits of stuff piled up for a long period of time” or “so that animals could scratch on them when they got itchy,” most of the 7- and 8-year olds chose the rocks’ usefulness for scratching to explain their shape (Kelemen, 1999). Thus, although children’s spontaneous questions indicate that they distinguish between animate and inanimate objects, their answers to “why” questions tend to ignore this distinction. Young children also often err in identifying which things are living and which are not. For example, most 5-year-olds say that plants are not alive, and some say that the moon and mountains are alive (Hatano et al., 1993). Erroneous notions such as these have led some investigators to conclude that children have only a shallow and fragmented understanding of living things until they are 7 to 10 years old (Carey, 1999; Slaughter, Jaakkola, & Carey, 1999). In contrast, other investigators believe that by age 5 years, children understand the essential characteristics of living things and what separates them from nonliving things (Gelman, 2003). A third view is that young children possess both mature and immature theories of living and nonliving things (Inagaki & Hatano, 2008). With this dispute in mind, we will now consider what young children do and do not know about living things and how they acquire knowledge about them. Distinguishing Living from Nonliving Things FIGURE 7. 4 Distinguishing people from nonliving things These photos show a task used by Poulin-Dubois (1999) to study infants’ reactions when they see people and inanimate objects (in this case a robot) engaging in the same action. Both 9- and 12-month-olds show surprise when they see inanimate objects move on their own, suggesting that they understand that selfproduced motion is a distinctive characteristic of people and other animals. BOTH: COURTESY OF DIANE POULIN-DUBOIS As noted previously, infants in their first year already are interested in people and distinguish them from nonliving things (Figure 7.4). Other animals also attract UNDERSTANDING WHO OR WHAT infants’ interest, though infants act differently toward them than they do toward people. Nine-month-olds, for example, pay more attention to rabbits than they do to inanimate objects, but they smile less at rabbits than they do at people (PoulinDubois, 1999; Ricard & Allard, 1993). These behavioral reactions indicate that infants in their first year distinguish people from other animals and that they distinguish both from inanimate objects. However, the reactions do not indicate when children construct a general category of living things that includes plants as well as animals or when they recognize humans as a type of animal. It is difficult to assess children’s knowledge of these and many other properties of living and nonliving things until the age of 3 or 4 years, when they can comprehend and answer questions about these categories. By this age, they clearly know quite a bit about the similarities among all living creatures and about the differences between living creatures and inanimate objects. This knowledge of living things is not limited to visible properties such as having legs, moving, and making distinctive noises. It also extends to biological processes such as digestion and heredity (Gelman, 2003). At least through age 5, however, many children have difficulty understanding that human beings are animals that are similar in many ways to other animals. They frequently deny that people are animals at all (Carey, 1985). Understanding the life status of plants also presents a challenge to young children. On the one hand, most preschoolers know that plants, like animals but unlike inanimate objects, grow (Hickling & Gelman, 1995; Inagaki & Hatano, 1996), heal themselves (Backscheider, Shatz, & Gelman, 1993), and die (Springer, Nguyen, & Samaniego, 1996). On the other hand, most preschoolers believe that plants are not alive; in fact, it is not until age 7 to 9 years that a clear majority of children realize that plants are living things (Hatano et al., 1993). Part of the reason is that children often equate being alive with being able to move in adaptive ways that promote survival, and the adaptive movements of plants (for example, their bending toward sunlight) are difficult to observe because they occur too slowly (Opfer & Gelman, 2001). Consistent with this interpretation, telling 5-year-olds that plants move toward sunlight and that their roots move toward water so that they can live leads the children to conclude that plants, like animals, are living things (Opfer & Siegler, 2004). More generally, culture and direct experience influence the age at which children understand that plants are, in fact, alive. For example, children growing up in rural areas realize that plants are living things at younger ages than do children growing up in cities or suburbs (Coley, 2000; Ross, Medin, Coley, & Atran, 2003). Understanding Biological Processes Preschoolers understand that biological processes, such as growth, digestion, and healing, differ from psychological and physical ones (Wellman & Gelman, 1998). For instance, while 3- and 4-year-olds recognize that desires influence what people do, they also recognize that there are biological processes that are independent of one’s desires. This distinction between psychological and biological processes, for example, leads preschoolers to predict that people who wish to lose weight but still eat a lot will not get their wish (Inagaki & Hatano, 1993; Schult & Wellman, 1997). Preschoolers also recognize that properties of living things often serve important functions for the organism, whereas properties of inanimate objects do not. Thus, 5-year-olds recognize that the green color of plants is crucial for them to make food, whereas the green color of emeralds has no function for the emerald (Keil, 275 276 CHAPTER 7 CONCEPTUAL DEVELOPMENT 1992). The extent of preschoolers’ understanding of biological processes can be understood more fully by examining their specific ideas about inheritance, growth, and illness. Inheritance Although 3- and 4-year-olds obviously know nothing about DNA or the mechanisms of heredity, they do know that physical characteristics tend to be passed on from parent to offspring. If told, for example, that Mr. and Mrs. Bull have hearts of an unusual color, they predict that Baby Bull also will have a heart of that color (Springer & Keil, 1991). Similarly, they predict that a baby mouse will eventually have hair of the same color as its parents, even if it is presently hairless. Older preschoolers also know that certain aspects of development are determined by heredity rather than by environment. For example, 5-year-olds realize that an animal of one species raised by parents of another species will become an adult of its own species ( Johnson & Solomon, 1996). Coexisting with this understanding are a variety of misguided beliefs about inheritance. Many preschoolers believe that mothers’ desires can play a role in their children’s inheritance of physical qualities, such as having blue eyes (Weissman & Kalish, 1999). Many preschoolers also believe that adopted children are at least as likely to look like their adoptive parents as like their birth parents (Solomon, Johnson, Zaitchik, & Carey, 1996). In other situations, preschoolers’ belief in heredity is too strong, leading them to deny that the environment has any influence. For example, preschoolers tend to believe that differences between boys and girls in play preferences are due totally to heredity (Taylor, 1993). Related to this general belief in the importance of heredity is one of the most basic aspects of children’s biological beliefs—essentialism, the view that living things have an essence inside them that makes them what they are (Gelman, 2003). Thus, most preschoolers (as well as most older children and adults) believe that puppies have a certain “dogness” inside them, kittens have a certain “catness,” roses have a certain “roseness,” and so on. This essence is what makes all members of the category similar to each other and different from members of other categories; for example, their inner “dogness” leads to dogs’ barking, chasing cats, liking to be petted, and so on. This essence is viewed as being inherited from one’s parents and being maintained throughout the organism’s life. Thinking in terms of such essences seems to make it difficult for both children and many adults to understand and accept biological evolution (Evans, 2008). If animals inherit an unchanging essence from their parents, how, they may wonder, would it be possible, say, for mice and whales to have common ancestors? ❚ essentialism ❚ the view that living things have an essence inside them that makes them what they are Growth, illness, and healing Preschoolers realize that growth, like inheritance, is a product of internal processes. They recognize, for example, that plants and animals become bigger and more complex over time due to something going on inside them (again, preschoolers are not sure what) (Rosengren, Gelman, Kalish, & McCormick, 1991). Three- and four-year-olds also recognize that the growth of living things proceeds in only one direction (smaller to larger) at least until old age, whereas inanimate objects such as balloons can become either smaller or larger at any point in time. Preschoolers also show a basic understanding of illness. Three-year-olds have heard of germs and have a general sense of how they operate. They know that eating food that is contaminated with germs can make a person sick, even if the person is unaware of the germs’ presence (Kalish, 1997). Conversely, they realize 277 © THE NEW YORKER COLLECTION 2000 LEE LORENZ FROM CARTOONBANK.COM UNDERSTANDING WHO OR WHAT “I’ve been getting in touch with the puppy in me.” A fanciful representation of the inner essence that children believe makes a dog a dog, a cat a cat, and so on. that psychological processes, such as being aware of germs in one’s food, do not cause illness. Finally, preschoolers know that plants and animals, unlike inanimate objects, have internal processes that often allow them to regain prior states or attributes. For example, 4-year-olds realize that a cat or a tomato plant that is scratched can heal itself but that a scratched car or chair cannot (Backscheider et al., 1993). They also know that when an animal’s hair is cut, it will grow back, but that if a doll’s hair is cut, it never will. On the other hand, they recognize the limits of such recuperative processes; they understand that both illness and old age can cause death, with death being a state from which no one recuperates (Nguyen & Gelman, 2002). How Do Children Acquire Biological Knowledge? As with other aspects of conceptual development, nativists and empiricists have very different ideas regarding the growth of children’s biological understanding. Nativists propose that humans are born with a “biology module” much like the theory of mind module described earlier in the chapter. This brain structure or mechanism helps children learn quickly about living things (Atran, 1990, 2002). Nativists support the idea that people have a biology module with three main arguments. earlier periods of our evolution, it was crucial for human survival that • During children learn quickly about animals and plants. throughout the world are fascinated by plants and animals and learn • Children about them quickly and easily. throughout the world organize information about plants and animals • Children in very similar ways (in terms of growth, reproduction, inheritance, sickness, and healing). Empiricists, in contrast, maintain that children’s biological understanding comes from their personal observations and from information they receive from parents, teachers, and the general culture (Callanan, 1990). When mothers in the United States read books about animals to their 1- and 2-year-olds, for example, many of the mothers’ comments and questions suggest that animals have intentions 278 CONCEPTUAL DEVELOPMENT and goals; that different members of the same species have a lot in common; and that animals differ greatly from inanimate objects (Gelman et al., 1998). Such parental teaching clearly contributes to children’s acquisition of biological knowledge. Empiricists also note that children’s biological understanding reflects the views of their culture. For example, 5-year-olds in Japan are more likely than their peers in the United States and Israel to believe that nonliving things and plants are able to feel physical sensations, such as pain and cold (Hatano et al., 1993). This tendency of Japanese children echoes the Buddhist tradition, still influential in Japanese society, which views all objects as having certain psychological properties. As with the parallel arguments regarding the sources of psychological understanding, both nature and nurture seem certain to play important roles in the acquisition of biological understanding. Young children are innately fascinated by animals and learn about them much more quickly than about aspects of their environment that they find less interesting. At the same time, the particulars of what children learn obviously are influenced by the information, beliefs, and values conveyed to them by their parents and their society. The challenge remains to specify how children integrate these aspects of nature and nurture to construct sophisticated biological concepts as rapidly as they do. review: The feelings of awe experienced by many children (and adults) upon seeing remains of great animals of the past and present, such as dinosaurs, elephants, and whales, were a major reason for the founding of natural history museums. Despite all the depictions of monsters and superheroes on television, in movies, and in video games, these fossils and models inspire the same sense of wonder in children growing up today. CHAPTER 7 From early in infancy, children form categories of similar objects. Such categorization helps them infer the properties of unfamiliar objects within a category. For example, if children learn that a new object is an animal, they know that it will grow, move, and eat. Children form new categories, and include new objects within an existing category, on the basis of similarities between the appearance and function of the new object and objects already known to be category members. One particularly important category is people. From the first days of life, infants are interested in other people and spend a great deal of time looking at them. By age 3 years, they form a simple theory of mind, which includes some understanding of the causal relations among intentions, desires, beliefs, and actions. Not until age 4 or 5 years, however, do most children become able to solve false-belief problems. The development of understanding of other people’s minds during the preschool period has been attributed to biological maturation of a theory of mind module, to interactions with other people, and to the growth of information-processing capabilities that allow children to understand increasingly complex social situations. Another vital category is living things. During the preschool years, children gain a basic understanding of the properties of biological entities: growth, heredity, illness, and death. Not until children go to school, however, do most of them group plants with animals into a single category of living things. Explanations for children’s relatively rapid acquisition of biological knowledge include the extensive exposure to biological information provided by families and the broader culture, as well as the existence of brain mechanisms that lead children to be interested in living things and to learn about them quickly and easily. UNDERSTANDING WHERE, WHEN, WHY, AND HOW MANY 279 Understanding Where, When, Why, and How Many Making sense out of our experiences requires accurately representing not only who or what was involved in an event, but also where, when, why, and how often the event occurred. To grasp the importance of these latter concepts, imagine what life would be like if you lost your understanding of any one of them—for example, your sense of time. Without a sense of time, you would not even know the order in which events occurred. Did you get dressed and then eat breakfast, or did you eat breakfast and then get dressed? Your whole impression of your life as a continuous stream of events would be shattered. Similar problems would arise if you lost your sense of space or causality or number. Reality would resemble a nightmare, in which order and predictability were suspended and chaos ruled. As described in the previous section, the categories that children need to answer the questions “Who?” and “What?” begin to be formed in infancy, though the understanding deepens for many years thereafter. Development of understanding of space, time, causality, and number follows a similar path. In each case, development begins in the first year of life, but major improvements continue throughout childhood and adolescence. Space Brain activation on a spatial reasoning task As illustrated by the presence of areas of high activation (the areas in color) in both the left and right sides of the brain images, spatial thinking engages both the right and left hemispheres of the brain. ZACKS, J.M., RYPMA, B., GABRIELLI, J., TVERSKY, B., & GLOVER, G. (1999). IMAGINED TRANSFORMATION OF BODIES: AN FMRI STUDY. NEUROPSYCHOLOGIA, 37(9), 1029–1040 The nativist/empiricist debate has been vigorous with regard to spatial thinking. Nativists argue that children possess an innate module that is specialized for representing and learning about space and that processes spatial information separately from other types of information (Hermer & Spelke, 1996; Hespos & Spelke, 2004). Empiricists, on the other hand, argue that children acquire spatial representations through the same types of learning mechanisms and experiences that produce cognitive growth in general; that children adaptively combine spatial and nonspatial information to reach their goals through moving around the enviroment; and that language and other cultural tools shape spatial development (Gentner & Broditsky, 2001; Newcombe & Huttenlocher, 2006). The two sides do agree on some issues. One point of agreement is that from early in infancy, children show impressive understanding of some spatial concepts, such as above, below, left of, and right of (Casasola, 2008; Quinn, 2005). Another common conclusion is that certain parts of the brain are specialized for coding particular types of spatial information. Contrary to the popular notion that spatial thinking occurs solely in the right hemisphere, spatial thinking actually occurs in both brain hemispheres. However, the two sides of the brain differ in the types of spatial information that they most actively process (Newcombe & Huttenlocher, 2000). Certain areas in the right hemisphere are especially active in processing fine-grain, continuous spatial information, such as the information used to recognize faces or to identify objects by means of touch (Wittelson & Swallow, 1988). In contrast, certain areas in the left hemisphere are especially active in processing categorical spatial information, such as the information that a particular object is in the bathroom or next to the television (Chabris & Kosslyn, 1998; Newcombe & Huttenlocher, 2000). The differentiation seems to be present from infancy onward. 280 CHAPTER 7 CONCEPTUAL DEVELOPMENT An aspect of spatial thinking that is of particular importance is how individuals code space both relative to themselves and relative to the external environment. Below we consider each of these types of spatial coding. Representing Space Relative to Oneself ❚ egocentric representations ❚ coding of spatial locations relative to one’s own body, without regard to the surroundings From early in infancy, children code the locations of objects in relation to their own bodies. As noted in Chapter 5, when young infants are presented with two objects, they tend to reach for the closer one (von Hofsten & Spelke, 1985). This shows that they recognize which object is closer, as well as the direction of that object relative to themselves. Over the ensuing months, infants’ representations of spatial locations become increasingly durable, enabling them to find objects they observed being hidden some seconds earlier. As discussed in Chapter 4, most 7-month-olds reach to the correct location for objects that were hidden under one of two identical covers 2 seconds earlier but not for objects hidden 4 seconds earlier, whereas most 12month-olds accurately reach for objects hidden 10 seconds earlier (Diamond, 1985). In part, these increasingly enduring object representations reflect brain maturation, particularly of the dorsolateral prefrontal cortex, an area in the frontal lobe that is involved in the formation and maintenance of plans and in the integration of new and previously learned information (Diamond & Goldman-Rakic, 1989; Nelson, 2006). However, the improved object representations reflect learning as well; infants who are provided a learning experience with a hidden object in one situation show improved location of hidden objects in other situations ( Johnson, Amso, & Slemmer, 2003). Note that all the preceding examples of infants’ ability to code space involve the infant remaining in a single location. Piaget (1971) proposed that this is the only kind of spatial coding that infants can do. The reason, according to his theory, is that the only representations infants are capable of forming during the sensorimotor period are egocentric representations, in which the locations of objects are coded relative to the infants’ immediate position at the time of the coding. As evidence, Piaget reported experiments showing that if infants repeatedly found a toy to their right, they would continue to turn right to find it, even if they were repositioned so that the object was now on their left. Subsequent studies have obtained similar findings. When 6- and 11-month-olds repeatedly see an interesting sight appear on their right, they initially continue to look to the right, even after they have been turned around 180 degrees so that the interesting sight is now on their left (Acredolo, 1978). Egocentric representation is not absolute, however: if toys are hidden adjacent to a distinctive landmark, such as a large tower, infants usually find the toy despite the change in their own position. Still, the question remains, How do children become able to find objects when their own position has changed and when no landmarks are available to guide their search? A major factor in helping infants acquire a sense of space independent of their own location appears to be self-locomotion. Thus, infants who crawl, or who have had experience propelling themselves in walkers, more often remember the locations of objects on the object permanence task (page 134) than do infants of the same age without such locomotor experience (Bertenthal, Campos, & Kermoian, 1994; Campos et al., 2000). Similarly, compared with infants who have not yet moved across rooms on their own, those infants who have done so show an earlier understanding of depth and drop-offs on the surfaces they travel; this is evidenced by acceleration in their heart rate as they approach the visual cliff in the procedure described on page 197. UNDERSTANDING WHERE, WHEN, WHY, AND HOW MANY 281 The reasons why self-locomotion enhances infants’ representation of space should be familiar to anyone who has both driven a car and been a passenger in one. Just as driving requires continuous updating of information about the surroundings, so does crawling or walking. In contrast, just as being a passenger in a car does not require such continuous updating of one’s location, neither does being carried. As would be expected from this analysis, self-locomotion also enhances older children’s spatial coding. Striking evidence for this conclusion emerged from a study in which kindergarten classmates were tested in the kitchens of their own homes (Rieser, Garing, & Young, 1994). Some of the kindergartners were asked to stand in place and imagine themselves walking from their seat in the classroom to the teacher’s chair and then turning around to face the class. Then they were asked to point from this imagined position to the locations within the classroom of various objects—the fishbowl, the alphabet chart, the coatroom door, and so on. Under these conditions, the 5-year-olds’ pointing was very inaccurate. Other kindergartners went through the same procedure, except that they were instructed to actually walk through their kitchen and turn around as they imagined themselves walking to the teacher’s chair and then turning to face the class. Under these conditions, the children’s pointing to the imagined objects in their imagined classroom was far more accurate. This result, like those described above with infants, highlights the interconnectedness of the system that produces self-generated motion and the system that produces mental representations of space (Adolph & Berger, 2006). Development of Spatial Concepts in Blind and Visually Impaired People Blind adolescents and adults, even those blind from birth, tend to have a quite accurate sense of space, which helps them move around the environment skillfully. ROBIN SACHS / PHOTOEDIT People often equate spatial thinking with vision, assuming that we can think spatially only about layouts that we have seen. Even in infancy, however, spatial thought can be based on senses other than vision and is possible when vision is not. Thus, when 3-month-olds are brought into a totally dark room in which they cannot see anything, they use sounds emitted by nearby objects to identify the objects’ spatial locations and reach for them (Keen & Berthier, 2004). Although infants can use their auditory sense, among others, to form spatial representations, visual experience during infancy does play an important role in spatial development. Evidence for this conclusion comes from cases in which surgery restored sight to people who were born either blind (Carlson, Hyvarinen, & Raninen, 1986) or with severely impaired vision due to cataracts that prevented patterned stimulation from reaching the retina (Le Grand, Mondloch, Maurer, & Brent, 2001, 2003). The surgery was performed early—on average at 4 months of age—and the people who underwent it had between 9 and 21 years of postsurgical visual experience before being tested. Despite their extensive visual experience after the corrective surgery, most of these people could not use visual information to represent space as well as other people can; problems remained, especially with representations of faces, even 20 years after the surgery (and thus after 20 years of visual experience). These findings do not mean that children who are born blind cannot represent space. They actually tend to have a surprisingly good spatial sense. On tasks involving the representation of very small spaces, such as being guided in drawing two sides of a triangle on a piece of paper and 282 CHAPTER 7 CONCEPTUAL DEVELOPMENT then being asked to complete the triangle by drawing the third side themselves, children who are born blind perform as well as sighted children who are blindfolded (Thinus-Blanc & Gaunet, 1997). On tasks involving representation of large spaces, such as those formed by exploring unfamiliar rooms, the spatial representations of people born blind also are surprisingly good, about as good as those formed by sighted people who were blindfolded during the exploration period. Thus, although some spatial skills seem to require early visual experience, many blind people develop impressive senses of space without ever seeing the world. Representing Space Relative to the External Environment As we have noted, infants as young as 6 months can use landmarks to code the location of objects they observe being hidden (Lew, Foster, Crowther, & Green, 2004). However, for such young infants to use a landmark successfully, it must be the only obvious landmark in the environment and must be located right next to the hidden object. With development, infants become increasingly able to choose among alternative potential landmarks. When 12-month-olds are presented a single yellow cushion, a single green cushion, and a large number of blue cushions, they have little trouble finding an object hidden under either the yellow or the green cushion (Bushnell, McKenzie, Lawrence, & Connell, 1995). At 22 months, but not at 16 months, the presence of a landmark improves children’s ability to locate an object that is not hidden adjacent to the landmark (Newcombe, Huttenlocher, Drummey, & Wiley, 1998). By age 5 years, children can also represent an object’s position in relation to multiple landmarks, such as when it is midway between a tree and a street lamp (Newcombe & Huttenlocher, 2006). Children, like adults, have more difficulty forming a spatial representation when they are moving around in an environment without distinctive landmarks or when the only landmarks are far from the target location. To understand the challenge of such tasks, imagine that you were walking in an unfamiliar city and did not remember exactly how you had arrived at your current location. How easily could you find your way back to your starting point? Even toddlers show the required navigational ability to some degree—good enough to lead them in the right general direction (Loomis et al., 1993). In one experiment, 1- and 2-year-olds first saw a small toy hidden in a long, rectangular sandbox and then saw a curtain descend around the sandbox, thus hiding the toy. The toddlers then walked to a different location, after which they were asked to find the toy. Despite no landmarks being present, the toddlers kept track of the hidden toy’s location well enough to show better than chance accuracy in their searches (Newcombe et al., 1998). On the other hand, forming relatively precise coding of locations in the absence of straightforward landmarks continues to be difficult for people well beyond 2 years of age (Bremner, Knowles, & Andreasen, 1994). Six- and seven-year-olds are not very good at it (Overman, Pate, Moore, & Peleuster, 1996), and adults vary tremendously in their abilities to perform this type of navigation. For example, when adults are asked to walk around the perimeter of an unfamiliar college campus and then to walk straight back to the starting point, some are quite accurate but many choose routes that take them nowhere near the original location (Cornell, Heth, Kneubuhler, & Sehgal, 1996). The degree to which people develop spatial skills is strongly influenced by the importance of such skills in their culture. To demonstrate this point, Kearins (1981) compared the spatial abilities of seminomadic aboriginal children growing up in the Australian desert with those of Caucasian peers growing up in Australian cities. Spatial ability is essential within aboriginal culture, because much of life within this culture consists of long treks between distant water holes. Needless to say, the aboriginals cannot rely on road signs; they must rely on their sense of space to get to the water. Consistent with the importance of spatial skills within their everyday lives, aboriginal children are superior to their citydwelling peers in memory for spatial location, even in board games, a context that is more familiar to the urban children (Kearins, 1981). Thus, consistent with the general importance of the sociocultural context, how people make use of spatial thinking in their everyday activities greatly influences their quality of spatial thinking. Time “What then is time? I know well enough what it is provided nobody asks me; but if I am asked and try to explain, I am baffled.” —St. Augustine, 398 C.E. (1963) As this quotation suggests, even the deepest thinkers, from St. Augustine who wrote in the fourth century to Albert Einstein who wrote in the twentieth, have been mystified by the nature of time. Yet even infants in their first half year have a rudimentary sense of time, including perception of both the order and the duration of events (Friedman, 2008). Experiencing Time Probably the most basic sense of time involves knowledge of temporal order, that is, knowing what happened first, what happened next, and so on. Not surprisingly, given how mystifying life would be without such a basic sense of time, infants represent the order in which events occur from as early as the capability can be effectively measured. In one study in which 3-month-olds were presented a series of interesting photos first on their left, then on their left, then on their right, and so on. Within 20 seconds, they began to look to the side where each new photo was to appear even before the photo was presented (Adler, Haith, Arehart, & Lanthier, 2008; Haith, Wentworth, & Canfield, 1993). This looking pattern indicated that 3-month-olds detected the repetitive sequence of events over time and used the information to form expectations of where the next photo would appear. In another experiment, 4-month-olds who were habituated to three objects falling and striking a surface in a constant order dishabituated when there was a change in the order in which the objects fell (Lewkowitz, 2004). By the end of their first year, infants can remember the order of events for a substantial period. For example, 10-month-olds who saw unusual pairs of actions repeated in the same order a number of times were able to imitate the actions in the correct order three months later (Carver & Bauer, 2001). By age 12 months, infants can see a pair of actions once and then imitate them in the correct order (Bauer, 1995). By 20 months of age, toddlers show similar proficiency with sequences of three events, clearly demonstrating that they can represent which came first, which next, and which last. PENNY TWEEDIE / PANOS PICTURES 283 UNDERSTANDING WHERE, WHEN, WHY, AND HOW MANY Spatial skills tend to be especially well developed in cultures in which they are crucial for survival. 284 CHAPTER 7 CONCEPTUAL DEVELOPMENT Infants also have an approximate sense of the durations of events. In one study, 4-month-olds saw periods of light and darkness alternate every 5 seconds for eight cycles, at which point the pattern was broken by the light’s failing to appear. Within half a second of the break, infants’ heart rates decelerated, a change, you will recall, that is characteristic of increased attention. In this case, the heart-rate deceleration suggested that the infants had a rough sense of the 5-second interval, expected the light to go on at the end of the interval, and experienced a spike in their attention when it did not appear (Colombo & Richman, 2002). Infants also can discriminate between longer and shorter durations. The ratio of the durations, rather than differences in their absolute length, is critical for these discriminations (Brannon, Suanda, & Libertus, 2007). For example, 6-month-olds discriminate between durations when their ratio is 2:1 (1 second versus .5 seconds or 3 seconds versus 1.5 seconds) but not when the ratio is 1.5:1 (1.5 seconds versus 1 second or 4.5 seconds versus 3 seconds). Over the course of the first year, the precision of these discriminations increases. Thus, 10-month-olds, unlike 6-month-olds, discriminate when the ratio of the durations is 1.5:1 (though not when it is 1.33:1). What about longer time periods—periods of weeks, months, or years? It is unknown whether infants have a sense of such long time periods, but preschoolers do possess some knowledge regarding them. For example, when asked which of two past events occurred more recently, most 4-year-olds knew that a specific event that happened a week before the experiment (Valentine’s Day) happened more recently than an event that happened seven weeks earlier (Christmas) (Friedman, 1991). However, preschoolers correctly answer such questions only when the more recent event is quite close in time and much closer than the less recent one. Ability to distinguish more precisely among the timing of past events develops slowly during middle childhood (Friedman, 2003). For example, when children who had been presented a distinctive classroom experience were asked three months later to recall the month in which the experience occurred, the percentage of correct recall increased from 20% among 5-year-olds to 46% among 7-year-olds to 64% among 9-year-olds (Friedman & Lyon, 2005). Understanding of the timing of future events increases during this age range as well (Friedman, 2000, 2003). Preschoolers often confuse the past and the future. For example, 5-year-olds predict a week after Valentine’s Day that the next Valentine’s Day will come sooner than the next Halloween or Christmas; they also predict that their next lunch is the same amount of time in the future regardless of whether they are tested just before lunch or just after it. Six-year-olds, in contrast, generally predict correctly in both cases. The improvement in children’s sense of future time between the ages of 5 and 6 years is probably influenced by 5-yearolds’ experience in kindergarten classrooms, where the cycle of seasons, holidays, and daily routines is emphasized. Children, like adults, are subject to certain illusions about time, in part because of the role of attention in time perception. When 8-year-olds’ attention is focused on the passage of time (for example, when they expect a prize at the end of a 2-minute interval), they perceive the duration as longer than the same interval when they are not anticipating a prize. Conversely, when they are very busy, they perceive the duration as shorter than when they have little to do (Zakay, 1992, 1993). Thus, the saying “A watched pot never boils” has psychological merit. UNDERSTANDING WHERE, WHEN, WHY, AND HOW MANY Reasoning about Time During middle childhood, children become increasingly proficient at reasoning about time. In particular, they become able to infer that if two events started at the same time, but one event ended later than the other, then the event that ended later must have lasted for a greater amount of time. Children as young as 5 years can sometimes make such logical inferences about time, but they do so only in simple, straightforward situations. For example, when told that two dolls fell asleep at the same time and that one doll awoke before the other, 5-year-olds reason correctly that the doll that slept later also slept longer (Levin, 1982). However, when 5-year-olds see two toy trains travel in the same direction on parallel tracks, and one train stops farther down the track, they usually say that the train that stopped farther down the track traveled for a longer time, regardless of when the trains started and stopped moving (Acredolo & Schmidt, 1981). The problem is that the 5-year-olds’ attention is captured by the one train being farther down the track, which leads them to focus on the spatial positions of the trains rather than on their relative starting and stopping times. If this observation reminds you of Piaget’s idea of centration (pages 137–138), there is good reason: Piaget’s (1969) observations of performance on this task were part of what led him to conclude that children in the preoperational stage often center on a single dimension and ignore other, more relevant ones. Causality The famed eighteenth-century British philosopher David Hume described causality as “the cement of the universe.” His point was that causal connections unite discrete events into coherent wholes. Consistent with Hume’s view, from early in development, children rely heavily on their understanding of causal mechanisms to infer why physical and psychological events occur. When children take apart toys to find out how they work, or ask how flipping a switch makes a light go on, or wonder why Mommy is upset, they are trying to understand causal connections. Both children and adults appear to have far deeper understanding of psychological causes than of physical ones; for example, kindergartners, 4th graders, and adults all can explain in much greater depth how people’s intentions influence their actions than how everyday devices such as toasters and gumball machines work (Keil, 2005; Mills & Keil, 2004). Because we discussed the development of understanding of psychological causes earlier in this chapter, we now focus on the development of understanding of physical causes. You probably will not be surprised to learn that nativists and empiricists disagree about the origins of understanding of physical causes. The difficulty of making sense of the world without some basic causal understanding, and the fact that children show some such understanding early in infancy, have led nativists to propose that infants possess an innate causal module or core theory that allows them to extract causal relations from the events they observe (e.g., Leslie, 1986; Spelke, 2003). Empiricists, on the other hand, have proposed that infants’ causal understanding arises from their observations of innumerable events in the environment (e.g., Cohen & Cashon, 2006; Rogers & McClelland, 2004). As in other contexts, the debate has stimulated many interesting observations and experiments, a few of which we will now review. 285 286 CHAPTER 7 CONCEPTUAL DEVELOPMENT Causal Reasoning in Infancy (a) (b) (c) (d) FIGURE 7.5 Imitating sequences of events Understanding the actions they are imitating helps toddlers perform the actions in the correct order. In this illustration of the procedure used by Bauer (1995) to demonstrate this point, a toddler imitates a previously observed three-step sequence to build a rattle. The child (a) picks up a small block; (b) puts it into the bottom half of the container; (c) pushes the top half of the container onto the bottom, thus completing the rattle; and (d) shakes it. ALL: COURTESY OF PATRICIA BAUER By 6 months of age, infants perceive causal connections among some physical events (Cohen & Cashon, 2006; Leslie, 1986). In a typical experiment demonstrating infants’ ability to perceive such relations, Lisa Oakes and Les Cohen (1995) presented 6- to 10-month-olds a series of video clips in which a moving object collided with a stationary object and the stationary object immediately moved in the way one would expect. Different moving and stationary objects were used in each clip, but the basic “plot” remained the same. After seeing a few of these video clips, infants habituated to the collisions. Then the infants were shown a slightly different clip in which the stationary object started moving before it was struck. Infants looked at this event for a longer time than they had looked during the preceding trials, presumably because the new video clip violated their sense that inanimate objects do not move on their own. Infants’ and toddlers’ understanding of physical causality influences not only their expectations about inanimate objects but also their ability to remember and imitate sequences of actions. When 9- to 11-month-olds are shown actions that are causally related (e.g., making a rattle by putting a small object inside two cups that can be pushed together to form a single container),…
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