Abstract

Humans manifest remarkable sensorimotor coordination abilities as showcased in the skilful performance expressed by orchestras and dance ensembles. In multi-agent interactions, sensorimotor loops that are normally involved in the control of one9s own movement must accommodate also for sensory data (e.g., visual feedback) informing about others9 movement to adjust performance and ultimately co-adapt to each other. Yet, a mechanistic understanding of how sensorimotor control comes into place to enable interpersonal coordination is still lacking. By examining movement intermittency, we here open a window into the dynamics of visuomotor loop control during interpersonal coordination. Specifically, we analysed submovements, i.e., recurrent (2-3 Hz) force pulses that are naturally engraved in our kinematics and deemed to reflect intrinsic intermittency in (visual-based) motor control. Participants were asked to synchronize rhythmic (0.25 Hz) finger flexion-extension movements. Besides synchronization at the common movement pace, finger velocity shows 2-3 Hz discontinuities that are consistently phase-locked between the two interacting partners. Notably, submovements alternate in a seemingly counterphase pattern, showing highest probability ~200ms before as well as after submovements generated by one9s partner. Further, when the real partner is replaced by an unresponsive partner - a dot moving according to a pre-recorded human kinematics - submovements systematically follow the dot submovements, indicating that movement intermittency is causally linked between partners. These results show that submovements are actively adjusted (inter-locked) during interpersonal coordination. Visuo-motor loop dynamics of interacting individuals can thus couple to optimize synchronization of the sense-and-correct process that is required for behavioural coordination.