Balancing out dwelling and moving : optimal sensorimotor 3 synchronization 4 5

24 Sensorimotor synchronization is a fundamental skill involved in the performance of many 25 artistic activities (e.g., music, dance). After a century of research, the manner in which the 26 nervous system produces synchronized movements remains poorly understood. Typical 27 rhythmic movements involve a motion and motionless phase (dwell). The dwell phase 28 represents a sizeable fraction of the rhythm period, and scales with it. The rationale for this 29 organization remains unexplained, and is the object of this study. Twelve participants, 4 30 drummers (D) and 8 non-drummers (ND), performed tapping movements paced at 0.5-2.5 Hz 31 by a metronome. The participants organized their tapping behavior into dwell and movement 32 phases according to two strategies: 1. Eight participants (1 D, 7 ND) maintained an almost 33 constant ratio of movement time (MT) and dwell time (DT) irrespective of the metronome 34 period; 2. Four participants increased the proportion of DT as the period increased. The 35 temporal variability of both the dwell and movement phases were consistent with Weber’s 36 law, i.e. their variability increased with their durations, and the longest phase exhibited 37 always the smallest variability. We developed an optimal statistical model that formalized the 38 distribution of time into dwell and movement intervals as a function of their temporal 39 variability. The model accurately predicted the participants’ dwell and movement durations 40 irrespective of their strategy and musical skill, strongly suggesting that the distribution of DT 41 and MT results from an optimization process, dependent on each participant’s skill to predict 42 time during rest and movement. 43 44