Brief articleAction experience alters 3-month-old infants' perception of others' actions
Introduction
The tendency to view action in terms of its underlying goal structure is pervasive in mature cognition. Adults and children organize their event memories around action goals (Newtson and Engquist, 1976, Zacks and Tversky, 2001), information about a protagonist's goals guides narrative construction and interpretation (Black and Bower, 1980, Trabasso et al., 1992), and goals and intentions serve as both explanatory constructs and predictive cues for describing our own and others' behavior (D'Andrade, 1987, Wellman, 1990). Sensitivity to the goal structure of action also plays a powerful role in mediating learning across a variety of domains. Goal understanding guides early word learning (Baldwin and Moses, 2001, Woodward, 2004), governs toddlers' social learning and problem-solving attempts (Carpenter et al., 1998, Carpenter et al., 2002, Meltzoff, 1995) and informs children's understanding of cultural instruments and artifacts (Bloom and Markson, 1998, Defeyter and German, 2003).
The capacity to detect the goal structure of events emerges during infancy. During the first year of life infants encode certain events as goal-directed, that is, they represent human actions (Sommerville and Woodward, 2005, Woodward, 1998, Woodward and Guajardo, 2002, Woodward and Sommerville, 2000, Woodward et al., 2001) and certain object motions (Csibra et al., 2003, Csibra et al., 1999, Gergely et al., 1995) with respect to the objects and outcomes to which they are directed, rather than in terms of their superficial perceptual properties. For instance, after watching an actor reach for and grasp a toy, infants show a stronger novelty response to a change in the actor's goal than a change in the spatial location or trajectory of her reach (Woodward, 1998). This basic ability to construe action with respect to external goals may form the cornerstone for an understanding of goals as abstract entities that guide human action and govern event sequences (Sommerville & Woodward, 2005). A critical question that emerges from this work concerns the experiences that contribute to infants' ability to view action as goal-centered. In the present study we focused on the role of infants' first-hand experience as agents in supporting their ability to construct goal-centered action representations.
Recent research suggests a candidate system that may contribute to the ability to view action as goal-directed. In non-human primates, neurons in the ventral premotor cortex (mirror neurons) are commonly activated both in the context of the production and observation of goal-directed action (e.g. Rizzolatti and Arbib, 1998, Rizzolatti and Fadiga, 1998), providing a means through which the goals of self and other acts are abstractly represented. A similar system has been documented in humans. Neuroimaging findings indicate an overlap in neural activation during action observation, execution and simulation (Grèzes & Decety, 2001) and behavioral measures indicate that perception and action share a common computational code (Hommel, Muessler, Aschersleben, & Prinz, 2001). Because this coupling between action and perception may emerge early in development (Meltzoff, 2002), it has been suggested that infants' ability to map from self to other (and vice versa) may serve as a catalyst for understanding their own and other's behavior in terms of goals (Meltzoff, 2002, Tomasello, 1999). Moreover, several authors have suggested that such a common coding system may play a foundational role in our understanding of others at an evolutionary level. For instance, it has been suggested that the mirror neuron system observed in non-human primates serves as a precursor to the construction of folk psychology (Gallese & Goldman, 1998) and that the action/perception matching system in mature humans supports intentional attribution via simulation (Blakemore & Decety, 2001).
These considerations, along with speculation regarding the central nature of action experience in cognitive development more broadly (Piaget, 1953), suggest that agentive experience may contribute to the construction of goal-centered action representations during infancy. Over the first year of life, infants' production of goal-directed acts becomes increasingly frequent, precise and refined. Information gleaned from these experiences may facilitate sensitivity to the goal structure of infants' own and others' actions. This action knowledge may subsequently be extended to allow infants to interpret a broad range of events with respect to goal structure. Such a role for action experience in the construction of goal-centered action representations predicts (a) a correlation between the emergence of goal-directed behaviors and infants' ability to detect goals in the acts of others, and (b) an impact of action experience on action interpretation.
Recent findings from our group provide evidence for the first prediction. During periods of emergence, individual variation in infants' action production correlates with their tendency to interpret observed actions of the same type as goal-directed. One study demonstrated this relation in the context of means-end sequences: 10-month-old infants' ability to pull a cloth to retrieve a toy in a systematic manner was related to their ability to identify the goal of a similar cloth-pulling sequence in the actions of another person (Sommerville & Woodward, 2005). A second study found a similar relation for the production and interpretation of points as object-directed (Woodward & Guajardo, 2002). These findings motivated us to test the second prediction.
We focused on infants' ability to detect the goal structure of a grasping event. Five to 6 months of age marks an emerging level of sophistication in infants' reaching ability, and it is around this same age that infants become sensitive to the goal structure of similar reaching acts performed by other people (Woodward, 1998). Prior to this age infants do not typically perform the smooth and efficient goal-directed reaches of older infants (Bertenthal and Clifton, 1998, Rochat, 1989), nor do they spontaneously encode the goal-directed structure of another persons' reach and grasp.1 To assess the potential reciprocal relation between action and perception, infants took part in an action task and a visual habituation procedure, and we assessed the impact of action experience on action perception and vice versa.
Section snippets
Participants
The participants were 30 healthy full-term 3-month-old infants. Infants ranged in age from 2 months, 29 days to 4 months 1, day. Infants were randomly assigned to either the reach-first condition, performing the action task prior to the habituation procedure (10 males and 5 females; mean age=3 months, 13 days) or the watch-first condition receiving the tasks in the reverse order (9 males and 6 females; mean age=3 months, 10 days).2
General discussion
The present findings demonstrate that infants rapidly learn from active experience and transfer this knowledge to visually observed events. We suggest that such findings reflect infants' ability to detect the goal structure of action following several minutes of intervention experience engaging in object-directed behavior, and to subsequently apply this knowledge to their perception of the actions of others. Thus, our findings add to the body of literature on rapid learning in young infants (
Acknowledgements
This work was supported by a NIH grant (R29-HD35707-01) to the second author. Correspondence should be sent to Jessica Sommerville, University of Washington, Institute for Learning and Brain Sciences, Campus Box 357988, Seattle, WA 98195; e-mail: [email protected].
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