11 Developmental Perspectives on Action Science: Lessons from Infant Imitation and Cognitive Neuroscience

ing Rules and Strategies from Others' Behaviors Another inference that adults make from seeing actions concerns the rules or strategies that govern the person's behavior. We might not imitate the precise details of another's actions but instead extract and adopt the rules they follow. One important activity used in everyday life and scientific endeavors involves the categorization of objects. People often embody categorization through a set of particular actions, sorting behavior, by which they separate objects into distinct piles according to their properties. Work by Williamson, Jaswal, and Meltzoff (2010) investigated whether 36-month-olds could learn different categorization strategies by watching the sorting behavior of another person. Children watched an adult sort objects. In one study, the adult sorted according to a visible property (color rather than shape). In a second study, she sorted by an invisible property (sounds made when shaken). In control groups, the experimenter presented a presorted array. Children who saw the adult sorting action sorted the objects (by color or sound) significantly more often than did the controls. This illustrates the power of imitation. Children can abstract from actions the underlying rules and strategies that generated them, and then can adopt those same rules to generate their own behavior. Based on these inferences, children begin to act like the others in their culture, for example, categorizing an array of objects along the same properties as done by an expert or acting in accord with the roles and cultural norms specified by society. Top-Down Control of Imitation Children do not imitate compulsively or blindly; imitation has its reasons. Recent laboratory work has unco:vered several top-down influences on imitation. 292 Andrew N. Meltzoff, Rebecca A. Williamson, and Peter J. Marshall Social Communication, Naive Pedagogy, and Emotions Older theories supposed that imitation was automatic, compulsory, and not subject to voluntary choice and control. Increasing evidence indicates, however, that even preverbal children regulate their imitation. In the simplest example, infants are more likely to imitate the actions of a model who engages them socially (Brugger, Lariviere, Mumme & Bushnell, 2007; Nielsen, 2006). Other studies suggest that the "mere belief" that a social agent caused an outcome yields an increase in infants' tendency to imitate it (Meltzoff, 2007b, experiment 3; see also Bonawitz et al., 2010; Meltzoff, Waismeyer & Gopnik, 2012; Thompson & Russell, 2004). Csibra and Gergely (2006; Gergely, 2011) have suggested that multiple cues, including eye contact and "motherese" intonational patterns, set up an expectation of a pedagogical exchange. Such social cues may draw attention to the relevant aspect of the adult's demonstratio~ and mark it as significant, thus changing the likelihood that it will be chosen for imitation (cf. Gergely, Bekkering & Kiraly, 2002; Paulus, Hunnius, Vissers & Bekkering, 2011; Zmyj, Daum, Prinz & Aschersleben, 2007). The emotional response that a person gives to an action also serves as a top-down controller of imitation. In one study, an adult performed a seemingly innocent act, and a second adult reacted with negative emotion (saying, "That is so irritating!") as if it were a "forbidden action." The experiment systematically manipulated whether the second adult was looking at the child when the child had a chance to imitate. Children did not imitate the forbidden action if the previously angry adult (now with a neutral face) was watching the child. If the previously angry adult left the room and could no longer visually monitor the child's action, the child would imitate (Repacholi & Meltzoff, 2007; Repacholi, Meltzoff & Olsen, 2008). This documents top-down regulation of imitation based on the expected emotional consequences of performing the action oneself. Self-Experience Another line of work shows that children regulate their imitation of actions depending on their own prior action experience. Williamson, Meltzoff, and Markman (2008) tested 36-month-old children to see if they were more likely to imitate an other person's actions if the child's own previous experience had revealed that the task was difficult. A surreptitious resistance device made a drawer difficult to open when the child first explored it. Then the adult demonstrated a distinctive technique for opening the drawer (pressing a button on the side of the box). Children were significantly more likely to imitate the adult's distinctive act if the child had a Developmental Perspectives on Action Science 293 prior difficult experience with the task. These results fit with educational philosophies asserting that self-experience confronting a problem can help the student be more open to instruction (see also Williamson & Meltzoff, 2011). Being Imitated: Social-Emotional Consequences Parent-child games are often reciprocal in nature, and mirroring games are a childhood favorite. What makes a child so engaged and joyful at seeing his or her own actions mirrored by an adult? Temporal contingencies are important, but so is the similarity of the form of the participants' actions. Research has investigated whether infants simply prefer people who are acting "just when they act" (temporal contingency) or whether they also prefer those who are acting "just like they act" (structuraI congruence). To test this idea, Meltzoff (2007a) had infants sit across a table from two adults. Both adults sat passively until the infant performed one of the target actions on a predetermined list. Then both experimenters began to act in unison, but one of the adults matched the infant, while the other performed a mismatching response. The results showed that the infants looked and smiled more at the matching adult. This shows that infants are sensitive to the matching form of the behavior. From a cognitive viewpoint, these findings are important because they show that the mechanisms underlying imitation are bidirectional. The machinery that takes visuaI input and generates a matching motor response can also run in reverse and recognize when the self's own actions are being mirrored. From a socia.1-emotional viewpoint, the findings are important because they show a social function of imitation. This research revealed that infants are visually engaged by, and have strong positive emotions toward, being imitated by someone else: infants smiled more at the imitator. Being imitated provides a nonverbal bond between the two actors, which may increase emotional attachment, prosocial feelings, and a sense of being understood. Adu.Its also have positive reactions to being imitated even when they are unaware of it (Chartrand & Bargh, 1999). A special "psychological jolt" is induced by seeing one's actions mirrored. Researchers have only just begun to perform the relevant neuroscience studies on being imitated by another person. Work in this area has been carried out with adults (Decety, Chaminade, Grezes & Meltzoff, 2002) and more recently with infants (Saby, Marshall & Meltzoff, 2012). In both cases, specific neural signatures were found for being imitated by another person. 294 Andrew N. Meltzoff, Rebecca A. Williamson, and Peter ). Marshall Cognitive Neuroscience and Action Science A comprehensive, contemporary action science requires an :11tegration of behavioral findings, cognitive theorizing, and neuroscience u~ ' '\. Much of the neuroscientific study of perception-action coordination ha. been driven by the concept of the mirror neuron system (MNS). This originates in the discovery, using single-cell recording techniques, of neurons in the ventral premotor cortex (FS) of macaque monkeys that respond not only when a monkey carries out a particular action on an object but also when the monkey observes the same action being carried out (di Pellegrino, Fadiga, Fogassi, Gallese & Rizzolatti, 1992; Rizzolatti, Fadiga, Gallese & Fogassi, 1996). Although a good deal of evidence exists for overlaps in patterns of regional brain activity between action perception and action production in human adults (Caspers, Zilles, Laird & Eickhoff, 2010; Hari & Kujala, 2009), researchers debate the function of this overlap and its relation to the macaque MNS. We do not aim to address these controversies here. Instead we focus on developmental issues, which have sometimes been overlooked. The corpus of behavioral work on infant imitation firmly establishes that young children link action perception and production. We can infer that some (as yet unspecified) neural circuitry supports such observation-execution coordination. A pressing question is how best to characterize the origins and development of these neural processes (Marshall & Meltzoff, 2011). EEG as a Tool in Action Science in Adults The developmental neuroscience work on action processing has mainly employed the electroencephalogram (EEG), with a focus on the sensorimotor mu rhythm. To understand this work, it is first useful to consider results from adult studies. In adults, the mu rhythm occurs in the alpha frequency range (8-13 Hz) and is typically recorded from central electrode sites overlying motor and somatosensory cortices. Early work showed a desynchronization (reduction in amplitude) of the mu rhythm during movement (Gastaut, Dongier & Courtois, 1954), with more recent work examining the specific time course of mu activity during voluntary actions (Pfurtscheller & Lopes da Silva, 1999). Building on recent magnetoencephalography (MEG) findings (Harl et al., 1998), studies with adults have further shown that the mu rhythm is also desynchronized during the observation of others' actions (e.g., Muthukumaraswamy & Johnson, 2004; Streltsova, Berchio, Gallese & Umilta, 2010). Taken together, these findings raise the Developmental Perspectives on Action Science 295 suggestion that the mu rhythm may be informative in the study of neural mirroring mechanisms