Temporal evolution of the phase correction response in synchronization of taps with perturbed two-interval rhythms.

Human sensorimotor synchronization is flexible but subject to temporal constraints. Previous research has shown that musicians tend to lose synchrony with target tones in an isochronous sequence when the sequence rate exceeds 8-10 Hz, presumably because phase correction ceases to function. The present study investigated directly the time required for an immediate phase correction response (PCR). Musicians tapped in synchrony with cyclic two-interval (short-long) rhythms, using the two hands in alternation. Perturbations were applied to the long interval, and the compensatory shift of the next tap (the PCR) was measured following the short interval, whose duration was varied from 100 to 300 ms. The PCR was found to increase gradually within this range, being nearly absent at 100 ms. Similar results were obtained when participants tapped only with the second tone in each rhythmic group, which confirms that the PCR is based on the preceding tone rather than on the preceding tap-tone asynchrony, and also when the second tone was omitted in the pacing sequence, which indicates that the PCR occurs automatically even when there is no synchronization target for the critical tap. These results extend earlier findings regarding rate limits of synchronization and also provide further support for an event-based phase resetting account of the PCR.