Attentional strategies and ancillary gestures in resisting unintentional synchronization during joint action

Humans exhibit a strong tendency to unintentionally synchronize their movements during joint activities. This poses a challenge in joint action settings when co-agents need to maintain some degree of temporal independence. We conducted two experiments with six expert musicians to investigate mechanisms supporting resistance to unintentional synchronization in complex polytempo music - a type of collective musical performance in which the individual musicians are required to play at different tempi. Study 1 manipulated visual coupling (musicians could or could not see each other) as well as whether the superposition of individual tempi produced a simple polyrhythm or a complex multi-tempo texture. Results showed that visual contact impaired how regular the musicians were when they played at independent tempi, suggesting that visual coupling increases the pull toward synchronization. Study 2 manipulated the degree of auditory coupling between the musicians through auditory attention as well as whether the musicians performed at identical or slightly different tempi. Here, heightened auditory attention did not impair stability when the musicians played at independent tempi, suggesting a potential asymmetry between visual and auditory modalities in driving unintentional synchronization. Across both studies, musicians' head movements - used as a proxy for ancillary gestures-were influenced by sensory coupling when the musicians had to play at different individual tempi. In particular, visual coupling led to a misalignment between the periodicity of the musicians' head movements and their own playing tempo, whereas increased auditory coupling was associated with larger head movements, potentially reflecting compensatory strategies. These findings highlight two mechanisms musicians may engage to resist synchronization: modulating the strength of the sensory coupling and reinforcing internal bodily coordination. The high ecological validity of the setup - featuring real instruments and ensemble performance - allowed us to identify these mechanisms in a realistic musical context. Beyond music, this work offers insights into how agents can intentionally resist synchronization to foster individual autonomy within collective actions, a phenomenon with implications for understanding creativity, coordination, and joint action.