Effects of emergent and planned interpersonal synchronization on individual spatiotemporal variability.

In real-life social exchanges, people synchronize movements via visuomotor information. How synchronizing voluntarily ('planned' synchronization) or involuntary ('emergent' synchronization) affects differently the variability of spatiotemporal movement parameters remains unclear. Here, we explored changes in the kinematics of pairs of participants performing a finger-tapping task in four full-within experimental conditions. In solo-pre and solo-post conditions, participants listened to a target tempo and individually reproduced it (unpaced) while blindfolded. In two social conditions, both participants had full vision of the partner's hand and concomitantly reproduced the target tempo while voluntarily synchronizing together (Synch condition) or resisting synchronization with the partner (Resist condition). Results revealed that participants co-adjusted taps and correlated finger movement peaks spatiotemporally in the social conditions and, crucially, individual variability lowered compared with the solo-pre condition. Moreover, the Synch condition revealed larger correlations and lower variability than the Resist one. Last, the partners' parameters no longer correlated in the solo-post condition and variability was similar to that of the solo-pre condition. This work unveils the importance of minimizing spatiotemporal variability for facilitating perception-action coupling during both emergent and planned interpersonal synchronization.