Multiple temporal references in sensorimotor synchronization with metrical auditory sequences.

A local phase perturbation in an auditory sequence during synchronized finger tapping elicits an automatic phase correction response (PCR). The stimulus for the PCR is usually considered to be the most recent tap-tone asynchrony. In this study, participants tapped on target tones ("beats") of isochronous tone sequences consisting of beats and subdivisions (1:n tapping). A phase perturbation was introduced either on a beat or on a subdivision. Both types of perturbation elicited a PCR, even though there was no asynchrony associated with a subdivision. Moreover, the PCR to a perturbed beat was smaller when an unperturbed subdivision followed than when there was no subdivision. The relative size of the PCRs to perturbed beats and subdivisions depended on tempo, on whether the subdivision was local or present throughout the sequence, and on whether or not participants engaged in mental subdivision, but not on whether or not taps were made on the subdivision level. The results show that phase correction in synchronization depends not merely on asynchronies but on perceptual monitoring of multiple temporal references within a metrical hierarchy.