There would be little that you and I would understand about the physical or so- cial world if we did not have a fundamental understanding that there are objects (including human objects, such as ourselves!) with substance and constancy, occupying locations in a spatial field. To become attached to a parent and to begin the process of healthy emotional development, a baby must have some conception of the parent as a permanent, substantive object in her world. (See Chapter 4 for an account of the infant’s ability to conceptualize the parent as a separate being.)
What must infants understand to “know” about objects—that is, to have an object concept? First, they need to know that objects have properties that can stimulate all of their senses: vision, hearing, taste, smell, and touch. For example, what they feel in their mouths as they suck a pacifier is the same as what they see when Mom or Dad holds the pacifier up in front of them. When can they make such connections? It appears that they have some capacity to do so as early as the 1st month of life. In a classic study, Meltzoff and Borton (1979) gave 1-month-olds an opportunity to suck on either a smooth pacifier or a bumpy one, without letting the infants see the pacifiers. Then, the researchers used the preferential looking paradigm to explore whether the babies had learned anything about the visual characteristics of the pacifiers that they had sucked on but had never seen. The babies looked at a split video screen. On one side was a picture of the smooth pacifier, on the other side a picture of the bumpy pacifier. A camera recorded the infants’ eye movements. The babies spent more time looking at whichever paci- fier they had previously sucked—suggesting that they were capable of identifying the appearance of the pacifier from their tactile experience of it. Findings like this one indicate that when young babies perceive an object in one way, they can construct some notion of the object’s other perceptual characteristics. This quality of intersensory integration (also referred to as cross-modal matching or inter- modal perception) is not surprising given what we now know about prenatal brain development. The development of one sensory system is influenced by the development of other systems (see the discussion of the brain in Chapter 2). Piaget (1954), without the benefit of today’s research methods, assumed that intersensory integration appeared later in infancy, after babies have learned to coordinate their reflexive responses to stimulation. For example, not until about 6 weeks do babies reach up to grasp an object that they are sucking; and not until 4 to 6 months do they smoothly coordinate grasping and looking, allowing easy exploration of ob- jects through visually guided reaching. Surely, these motor coordinations enrich a baby’s understanding of objects as “packages” of perceptual characteristics, but such understanding is initiated earlier than Piaget realized.
What else must infants know to have an understanding of objects? Piaget pointed out that adults realize that objects have a separate existence from the per- ceiver. Think for a moment about something that is out of sight, like the sink in your bathroom. Despite your inability to see the sink at this moment, you realize that it
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It can be argued that to understand the permanence of objects, a child must have at least a rudimentary capacity to keep the object in mind when it is not pres- ent. To put it another way, the child must have a mental representation of the object, like your mental image of the bathroom sink. The capacity to think about things or events that are not currently stimulating our senses is called representational thought. Thus, if we could find out when a baby understands object permanence, we would not only know something about her object concept, but we would also know that she was capable of representational thought. Piaget invented the hidden object test to assess object permanence. An interesting object, like a small toy, is placed in front of a baby, within her reach. As the baby watches, we cover the object with a cloth, so that it is out of sight. What we want to know is, will the baby search for the object under the cloth, or does the baby act as if the object’s disappearance means that the object no longer exists? Studies using the hidden object test, begin- ning with Piaget’s own studies, have consistently found that infants younger than 8 to 12 months fail to search for the object, even though they have the motor skills they need to succeed much earlier (e.g., they engage in visually guided reach- ing by about 4 months, and they can sit without support by about 6 months). Piaget concluded that understanding object permanence has its rudimentary begin- nings late in the 1st year of life and gradually improves thereafter. He also inferred that representational thought—the ability to form mental representations, such as images—is a skill that begins to develop only in the late months of the 1st year of life. Piaget’s work demonstrated that representational ability improves through the 2nd year of life, until, by the end of the sensorimotor period, children not only think about objects but can mentally plan their actions, solve simple problems “all in their heads,” remember past experiences, and so on. In other words, they have developed a broad capacity for thinking.
In recent years, studies using procedures such as the habituation paradigm have indicated that babies may have some understanding of object permanence, and therefore, perhaps, some representational thinking skills, much earlier in infancy. For example, Aguiar and Baillargeon (1999, 2002) showed infants a display with a doll standing to the left of one screen (see Figure 3.1). To the right of the screen was a space and then another screen. Babies watched as the doll moved toward the first screen and disappeared behind it. Even 2 1⁄2-month-olds acted surprised
if the doll reappeared to the right of the second screen, without ever being visible
Doll disappears
behind first screen. Doll emerges frombehind second screen.
FIGURE 3.1 Stimuli for a test of object permanence by aguiar and Baillargeon. SOURCE: Aguiar, A., & Baillargeon, R. (1999). 2.5-month-old infants’ reasoning about when objects should and should not be occluded. Cognitive Psychology, 39, 116–157. Used with permission from Elsevier.
Infants across cultures develop an understanding of object permanence at approximately the same age, beginning around the end of the first year of life.
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Publishing Servicesin the space between the screens. You and I would be surprised as well, expecting the doll to follow a normal trajectory, emerging from behind the first screen, con- tinuing to move to the right before disappearing again behind the second screen, and then emerging at the far right. If 2 1⁄2-month-olds expect hidden objects to fol-
low that trajectory as well, perhaps young babies understand that objects continue to exist when they cannot be seen.
Studies by Baillargeon and her colleagues (see Baillargeon, 2000), as well as other infancy researchers, have created lively controversy about just when repre- sentational thinking begins (see discussions by Haith & Benson, 1998; Kagan, 2002; Mandler, 2004) and about what aspects of objects young babies are likely to repre- sent (e.g., Kibbe & Leslie, 2011; Wilcox, Haslup, & Boas, 2010). Nonetheless, there is general agreement that thinking, and conceptual developments that are dependent on thinking, such as object permanence, gradually improve through the 1st and 2nd years of life and beyond (see Cohen & Cashon, 2006). In the next section, we will see that studies of infant memory and of babies’ abilities to plan their actions indi- cate the same kind of gradual development.
remembering
New research on infant memory is becoming available at a very rapid rate, stimulated by the availability of methods such as the habituation and preferential response para- digms and by the special interest of researchers who favor information processing theories of cognitive development (see Chapter 1). Storage of information, duration of storage, retrieval of stored information—these are the centerpieces of cognitive functioning from the point of view of scientists who think about the human cognitive system as akin in some ways to a computer processor. Their special interest has pro- vided us with a much better picture today of what infants can learn and remember than we had 20 years ago. What follows is only a sampling of what we are discover- ing about infant memory, that is, the ability to learn and to store information.
First, memory is not just one mental function. There are different kinds of memory. Here we will describe two: recognition and recall. Recognition memory is the ability to differentiate between experiences that are new and experiences that we have had before. When you see a face across a room and say to yourself, “I’ve seen that person before,” you are demonstrating recognition. Piaget (1952) guessed from the way babies use their reflexes that at least a primitive form of recognition is possible in earliest infancy. Babies will suck anything that touches their lips, but if they are hungry, they continue to suck only objects that have become associated with nourishment, like nipples. Thus, they show a kind of motor recognition of the nipple through their sucking.
Today’s researchers typically use the habituation paradigm to assess infant rec- ognition. When babies habituate to a stimulus that is repeatedly presented, they are showing us that the stimulus is becoming familiar. Because even newborns will habitu- ate to at least some repeatedly presented stimuli, we are now confident that newborns are capable of recognition. Operant conditioning has also demonstrated that recogni- tion skills are present from birth. For example, a 3-day-old infant will learn to suck harder for the reward of hearing its own mother’s voice (rather than a stranger’s voice), indicating that the baby recognizes the mother’s voice (e.g., DeCasper & Fifer, 1980). The newborn’s recognition of the mother’s voice seems to be a result of opportunities to hear her voice before birth, suggesting that the capacity for recognition is already in place before birth (DeCasper & Prescott, 1984; DeCasper & Spence, 1986).
Recognition improves throughout infancy. In many instances, recognition in the newborn period fades after a few minutes or even seconds, although some stud- ies have found much longer durations (e.g., DeCasper & Spence, 1986). If infants are 3 months old or older when they are exposed to a stimulus, they sometimes rec- ognize it after several months of nonexposure, especially if it is a moving stimulus (e.g., Bahrick & Pickens, 1995).
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Publishing ServicesNot only does the duration of recognition increase with age, but the speed with which babies habituate increases as well. Younger babies need more exposures to a stimulus than older babies before they show signs of recognition. But there are also individual differences among babies of the same age. Interestingly, how quickly babies habituate to a new stimulus is one of the few measures of infant functioning that has been found to correlate with later intelligence test performance. Apparently, recognition speed is an early indicator of the efficiency with which a child may later process information (Bornstein & Colombo, 2010).
In contrast to the early and rapid development of recognition memory, recall seems to emerge later in infancy. Recall is the ability to bring to mind an experience that has happened in the past. It is different from recognition because the to-be- remembered experience is not presently occurring, but must be mentally represented. In other words, thinking that involves mental representation, such as forming mental images, is necessary for recall. One indicator of recall is deferred imitation, in which children observe the actions of another on one occasion, and then imitate those ac- tions sometime later. We should note that babies imitate some immediate actions as early as the newborn period. For example, if you stick out your tongue at a newborn, you are likely to see the baby’s tongue protrude as well (Meltzoff & Moore, 1977), an action that is often interpreted as a reflexive response to a looming stimulus (e.g., Mandler, 2004). But soon babies will imitate other actions. If you clap your hands at a 4-month-old, she may clap her hands as well (Piaget, 1951). It seems that babies slowly work out the correspondences between their own and other people’s body parts, and as they do, they extend their range of imitation. (See Box 3.2 for a possible brain mechanism that supports this process.) But immediate imitation does not indicate recall. Only if there is a time delay between the observed action and the baby’s imita- tion of it can we say that representations in memory were necessary for the imitation. Based on observations of his own children’s behavior, Piaget believed that deferred imitation begins around the middle of the baby’s 2nd year. At 16 months, for example, his daughter Jacqueline watched a visiting boy have a temper tantrum, screaming and stamping his feet in a playpen. The next day, Jacqueline did the same, only she was smiling and her foot stamping was gentle. She was not actually having a temper tantrum, but was imitating her little friend’s fascinating perfor- mance (Piaget, 1962). More recent research demonstrates that infants from about 9 months of age will recall, and later imitate, actions that they have witnessed. For example, Meltzoff (1988) showed babies an interesting box, then demonstrated that pushing a button on the box would produce a beep. The next day, the babies were given the opportunity to play with the box themselves for the first time. Nine- month-old babies who had watched the button pushing the previous day were much more likely to push the button themselves than were babies who had not previously observed the action. On the whole, available research suggests that de- ferred imitation can begin late in the 1st year but that it does improve dramatically over the next year, both in duration and in the complexity of what can be recalled. For example, 11-month-old babies will imitate a simple action as long as 3 months later, but 20-month-olds can imitate more elaborate sequences as long as 12 months later (see Bauer, 2006). Deferred imitation is, of course, what makes observational learning, or modeling, possible (see Chapter 1). Once children can mentally repre- sent and thus recall the actions of others, they have a cognitive skill that is critical for social learning. A toddler who has watched his big sister painting pictures might on his own open a jar of paint, dip a paintbrush into it, and then sweep the paint- brush across some available surface. His proficiency at each of these actions will be limited, but the sequence will be executed more or less correctly because he recalls his big sister’s past actions.
Searching for a hidden object, which begins at about 8 months of age, can be seen as a sign not only that a child believes in the object’s permanence but that the child recalls the object. A particularly important sign of such recall is the beginning of separation anxiety. When parents leave a young baby with another caregiver,
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Publishing ServicesSuppose we offered a monkey a piece of food and the monkey reached out to grasp it. And suppose that at the same time, we were recording the activity of individual neurons in the monkey’s motor cor- tex via tiny electrodes implanted in those neurons. If we were record- ing in the right location, we would find that certain neurons fire when the monkey executes the grasping action. Using this kind of single-cell recording technique, a team of Italian researchers discovered a remarkable group of brain cells they called mirror neurons (e.g., Rizzolatti, Fadiga, Fogassi, & Gallese, 1996). These neurons, located pri- marily in motor cortex, were activated (fired) not only when a monkey performed a particular action, like grasping, but also when the monkey saw someone else, a person or a monkey, perform that action on an object. These neurons appear to help monkeys understand the actions of others. Rizzolatti and Craighero (2004) explain it this way:
Each time an individual sees an action done by another in- dividual, neurons that represent that action are activated in the observer’s premotor cortex. This automatically induced, motor representation of the observed action corresponds to that which is spontaneously generated during active ac- tion and whose outcome is known to the acting individual. Thus, the mirror system transforms visual information into knowledge (p. 172).
Do people also have mirror neurons that help them understand the actions of others? Single-cell recording is too invasive a procedure to use with healthy people, but electroencephalography and other psy- chophysiological techniques, such as brain imaging, can safely mea- sure the activation of broader areas of the brain. Many studies using these methods demonstrate that parts of human motor cortex, which is activated when someone performs an action, are also activated when the individual observes someone else performing the same action. So humans, too, have mirror neurons, and they probably do for
humans what they do for monkeys. That is, they help us to understand the actions of others. But in human brains the mirror neuron system appears to be much more extensive than in monkeys (Molenberghs, Cunnington, & Mattingly, 2012), and it contributes to some capacities that are more uniquely human, such as our ability to learn how to do things by imitating the actions of others (Ferrari & Fogassi, 2012).
How could mirror neurons support the ability to imitate? It may work something like this. If you observe someone else performing an action, aspects of that experience are recorded in a group of mir- ror neurons. Mirror neurons can also trigger action—they have mo- tor properties—so if these neurons encode the observed action, they can initiate our own, similar action, or help us plan such an action. Sometimes mirror neurons activate our own muscles at a minimal level even when we do not enact the full motion. For example, have you ever noticed that when you watch someone make a sad or happy face, your own facial muscles seem primed to mimic that expression?
In addition to imitation, mirror neurons appear to facilitate other skills that begin in infancy and early childhood, such as the develop- ment of gaze following, intention understanding, language, and em- pathy (see Rizzolatti & Craighero, 2004; Triesch, Jasso, & Deak, 2007). Their special property of both recording others’ actions and partici-