Balancing out dwelling and moving: optimal sensorimotor synchronization

International audienceSensorimotor synchronization is a fundamental skill involved in the performance of many individual and ensemble artistic tasks (e.g., music, dance). Separate theories may explain how time intervals are estimated, and how bodily displacements toward spatial goals are controlled. However, the manner in which the nervous system produces movements toward concomitant temporal and spatial goals remains poorly understood. Previous studies have shown that typical rhythmic movements involve a motion and motionless phase (dwell). The dwell phase represents a sizeable fraction of the rhythm period, and scales with this period. The rationale for this specific organization remains unexplained, and is the object of this study. Two groups of participants (drummers, non-drummers) performed tapping movements paced at 0.5-2.5 Hz. The participants consistently organized their behavior between acoustic cues into dwell and movement phases, and movement kinematics varied with the period of the rhythm, yielding velocity profiles becoming increasingly asymmetric as the period expanded. The main new results were that the temporal variability of both the dwell and movement phases were consistent with Weber's law, and the longest phase exhibited always the smallest variability. We developed an optimal statistical model that formalized the distribution of time into dwell and movement intervals as a function of their temporal variability. The model accurately predicted the participants' dwell and movement durations irrespective of musical skill, strongly suggesting that the distribution of dwell and movement intervals results from an optimization process, dependent on each participant's skill to predict time during rest and movement