Rhythmic Structure Shapes Dyadic Self-Other Representations Through Interpersonal Action Coupling.

Moving in unison to a musical beat can blur boundaries between individual movements, fostering prosociality. However, structured patterns of sounds and silences in rhythms (meter) allow various ways of moving to the beat. How do these different rhythmic interpretations affect social connectedness? Unacquainted dyads drummed in unison, and at more complex integer multiple and polyrhythmic ratios. Coordination requires continuously tracking who does what and when. We varied trackability by manipulating task-sharing (the same or separate drum pads, and audible or inaudible partner drumming). More complex ratios decreased social connectedness. However, coordination revealed a dichotomy between unison and the more complex ratios: in unison drumming, participants automatically tracked and adjusted to each other's actions, but both integer multiples and polyrhythms separated the two participants' actions in time, allowing one to be stable despite their partner being variable. Hearing each other increased participants' mutual reliance on each other's actions, but by itself did not increase connectedness. However, sharing a drum pad and audio significantly boosted self-other merging ratings. Notably, more stable coordination facilitated integrated self-other representations. Our findings are consistent with the premise that meter provides a shared cognitive-motor scaffold that enables group cohesion, while simultaneously allowing individual expression through multi-part rhythm production.