Social Effects of Movement Synchrony: Increased Infant Helpfulness only Transfers to Affiliates of Synchronously Moving Partners

Interpersonal synchrony increases cooperation among adults, children, and infants. We tested whether increased infant helpfulness transfers to individuals uninvolved in the movement, but shown to be affiliates of a synchronously moving partner. Initially, 14‐month‐old infants ( N  = 48) watched a live skit by Experimenters 1 and 2 that either demonstrated affiliation or individuality. Infants in both groups were then randomly assigned to be bounced to music either synchronously or asynchronously with Experimenter 1. Infant instrumental helpfulness toward Experimenter 2 was then measured. If the two experimenters were affiliates, infants from the synchronous movement condition were significantly more helpful toward Experimenter 2 than infants from the asynchronous movement condition. However, if the two experimenters were not affiliated, synchrony effects on prosociality did not transfer to Experimenter 2. These results show the importance of musical synchrony for social interaction and suggest that infants may use an understanding of third‐party social relationships when directing their own social behaviors.