Flexible Multimodal Synchrony during Joint Drumming Reflects Interaction Demands and Social Connection

In a society that relies on collaborative interactions to foster innovation and connection, understanding how interpersonal dynamics relate to social relationships is critical. Central to effective social collaboration is interpersonal synchrony—the temporal alignment of biobehavioral processes between individuals—which can support feelings of closeness and cooperative engagement. Synchrony is modulated by different social interaction contexts, raising questions about when and why dynamical variations to synchrony occur and their implications for relationships. Furthermore, it remains unclear if different measures of neurophysiological synchrony integrate to similarly predict social closeness. In this study, we explored how two distinct measures of neurophysiological synchrony (heart rate and neural alpha-band) between pairs of strangers engaging in joint drumming tasks varied across different task contexts characterized by different degrees of social engagement and structure. 100 participants - nested in 50 dyads - completed three interactive phases designed to vary in social demands and structural constraints. Results indicated that both heart rate and alpha synchrony significantly increased during the interactive phases compared to non-active baseline periods. Additionally, synchrony levels differed across the task’s interactive phases, highlighting meaningful distinctions in how synchrony responds to subtle contextual changes in task demands. Alpha synchrony was highest in the more structured beat entrainment stage, whereas heart rate synchrony increased across all interactive stages, with the highest levels observed during structured social engagement. Further, synchrony measures exhibited intra- and cross-modal correlations, reflecting integrated biobehavioral alignment. Both neural and physiological synchrony predicted perceived closeness overall. A stage-by-stage analysis revealed that heart rate synchrony consistently predicted closeness across all interactive stages, whereas neural synchrony predicted closeness exclusively during a free improvisation stage of joint drumming. Collectively, these findings illuminate the critical role of contextual motivations for structure and connection in shaping interpersonal synchrony and, ultimately, social closeness, with implications for enhancing social connection in educational, clinical, and organizational settings.