Infants understand collaboration: Neural evidence for 9-month-olds' attribution of shared goals to coordinated joint actions.

Interpreting others' actions as goal-directed, even when the actions are unfamiliar, is indispensable for social learning, and can be particularly important for infants, whose own action repertoire is limited. Indeed, young infants have been shown to attribute goals to unfamiliar actions as early as 3 months of age, but this ability appears restricted to actions performed by individuals. In contrast, attributing shared goals to actions performed by multiple individuals seems to emerge only in the second year of life. Considering the restrictions that this would impose on infants' understanding and learning from interactions in their environment, we reexamine this ability by introducing 9-month-old infants to simple joint actions, in which two agents coordinate their actions toward the same goal. To establish whether infants formed an expectation about future actions of these agents, infants' cortical activity was measured using functional near-infrared spectroscopy (fNIRS). The hemodynamic response, recorded in (p)STS, indicated that infants attributed goals to simultaneous and coordinated joint actions of two individuals. Thus, even prior to actively engaging in collaborative activities themselves, infants can attribute shared goals to observed joint actions, enabling infants to learn from, and about, the complementary roles of social interactions, a central characteristic of human culture.