Understanding how movement signals shape early social coordination and learning.

From early in life, social interactions rely on a rich exchange of nonverbal information. This review paper focuses on the nonverbal, kinematic information conveyed by how social partners move and proposes that such movement modulations may facilitate interpersonal coordination between infants and adults, as well as support infants' learning in early interactions. So far, findings on movement modulations have been investigated in isolation: sensorimotor communication in interpersonal coordination between adults (signaling) on the one hand, and in early teaching interactions between adults and infants (motionese) on the other. This paper integrates these findings and argues that both forms of movement-based communication operate along a continuum of predictability and surprise, which are flexibly adapted depending on the underlying social goal, i.e., interpersonal coordination or teaching. This leads to testable hypotheses on how predictability and surprise in adult movements could support infants' real-time action prediction and, consequently, their learning and optimization of interpersonal coordination, with a potential impact on social development in the long run. By integrating empirical findings from distinct research lines, the present review offers a novel framework to investigate how early social interactions and learning may be shaped by movement-based communication, opening new avenues for exploring developmental trajectories.