Timing precision in continuation and synchronization tapping

Wing and Kristofferson (1973) have shown that temporal precision in self-pa ced tapping is limited by variability in a central timekeeper and by Variab ility arising in the peripheral motor system. Here we test an extension of the Wing-Kristofferson model to synchronization with periodic external even ts that was proposed by Vorberg and Wing (1994). In addition to the timekee per and motor components, a linear phase correction mechanism is assumed wh ich is triggered by the last or the last two synchronization errors. The mo del is tested in an experiment that contrasts synchronized and self-paced t rapping, with response periods ranging from 200-640 ms. The variances of ti mekeeper and motor delays and the error correction parameters were estimate d from the auto-covariance functions of the interresponse intervals in cont inuation and the asynchronies in synchronization. Plausible estimates for a ll parameters were obtained when equal motor Variance was assumed for synch ronization and continuation. Timekeeper variance increased with metronome p eriod, but more steeply during continuation than during synchronization, su ggesting that internal timekeeping processes are stabilized by periodic ext ernal signals. First-order error correction became more important as the me tronome period increased, whereas the contribution of second-order error co rrection decreased. It is concluded that the extended two-level model accou nts well for both synchronization and continuation performance.