Processes underlying adaptation to tempo changes in sensorimotor synchronization

In synchronizing finger taps with an auditory sequence, a small sudden tempo ("step") change in the sequence tends to be followed by rapid adaptation of the tapping period but slow adaptation of the relative phase of the taps, whereas a larger step change leads to initial period overshoot followed by rapid adaptation of both period and phase [M.H. Thaut, R.A. Miller, L.M. Schauer, Biological Cybernetics 79 (1998a) 241-250]. Experiment 1 replicated these findings and showed that the transition between the two patterns of adaptation occurs near the perceptual detection threshold for a tempo change. A reasonable explanation of these data was provided by a dual-process model of internal error correction [J. Mates, Biological Cybernetics 70 (1994a) 463-473, 70 (1994b) 475-484], with the added assumption that one process (period correction) depends on conscious awareness of a tempo change whereas the other (phase correction) does not. This assumption received support in Experiment 2, where a synchronization-continuation tapping task was used in combination with perceptual judgments to probe into the process of period correction following step changes. The results led to the conclusion that rapid adaptation of the tapping period to a small, undetected tempo change is in fact due to rapid internal phase correction, whereas slow adaptation of the relative phase of the taps is due to slow internal period correction.