Tuning in Sensorimotor Synchronization

Moving in synchrony to external rhythmic stimuli is an elementary function that humans regularly engage in. It is termed “sensorimotor synchronization” and it is governed by two main parameters, the period and the phase of the movement with respect to the external rhythm. There has been an extensive body of research on the characteristics of these parameters, primarily once the movement synchronization has reached a steady-state level. Particular interest has been shown about how these parameters are corrected when there are deviations for the steady-state level. However, little is known about the initial “tuning-in” interval, when one aligns the movement to the external rhythm from rest. The current work investigates this “tuning-in” period for each of the four limbs and makes various novel contributions in the understanding of sensorimotor synchronization. The results suggest that phase and period alignment appear to be separate processes. Phase alignment involves limb-specific somatosensory memory in the order of minutes while period alignment has very limited memory usage. Phase alignment is the primary task but then the brain switches to period alignment where it spends most its resources. In overall this work suggests a central, cognitive role of period alignment and a peripheral, sensorimotor role of phase alignment. Highlights In the tuning-in phase there are three distinct temporal scales of sensorimotor synchronization with distinct signatures. A long-range, across-blocks monotonic negative gradient to more anticipatory movement, which prevails for tens of minutes, a very consistent “hook”-shaped pattern within each block, in the range of seconds, and a constant difference across time between feet and hands. The across-blocks, monotonic, negative gradient to more anticipatory movement is instantiated only in the first anticipatory trial of each block and the rest of the subsequent block trials contribute to the alignment of the inter-movement interval to the metronome’s period. This negative asynchrony gradient is limb-specific and is not affected by the interleaved blocks of other limbs. Period alignment has a central, cognitive role while phase alignment a peripheral, sensorimotor role.