Interpersonal synchrony affects 18-month-olds' social alignment via self-other comparison

Human infants are geared towards others in their environment, use others to select what to learn, and are selective in who they learn from. How infants relate to others is affected by a range of factors in social interactions, one of which is interpersonal synchrony: infants prefer synchronous social partners and are more willing to help others they moved in synchrony with. Here, we investigated whether interpersonal synchrony affects infants' imitation and social alignment, around the age when they develop a self-concept. As a marker of self-concept, we first administered the mirror self-recognition test. Then infants were bounced (a-)synchronously with an experimenter. Next, they saw the same experimenter wearing a sticker on her face and could choose between two stickers, one matching the experimenter's. Infants who showed evidence for a cognitive self were more likely to choose the matching sticker following asynchronous movement. Possibly, a conceptual self allows them to appreciate that they can actively intervene to bring about alignment. Infants also pointed more following asynchrony, suggesting that self-other distinction may sensitize infants to consider others' distinct perspective. In the imitation task, infants in the synchrony condition were somewhat more likely to imitate the suboptimal actions of the experimenter, indicating that interpersonal synchrony may enhance social learning. We conclude that interpersonal synchrony can highlight self-other similarity or lack thereof to infants - an important social cue that affects how they align with others, communicate and learn from them, especially once they are able to conceive of their own self.