Variability in isochronous tapping: Higher order dependencies as a function of intertap interval

lsochronous serial interval production (ISIP) data, as from unpaced finger tapping, exhibit higher order dependencies (drift). This fact has largely been ignored by the timing literature, one reason probably being that influential timing models assume random variability. Men and women, 22-36 years old, performed a synchronization- continuation task with intertap intervals (ITI) from 0.4 s to 2.2 s. ISIP variability was partitioned into components attributable to drift and Ist-order serial correlation, and the results indicate that (a) drift contributes substantially to the dispersion for longer ITIs, (b) drift and I st-order correlation are different functions of the ITI, and (c) drift exhibits break close to 1.0 s and 1.4 s ITI. These breaks correspond to qualitative changes in performance for other temporal tasks, which suggests common timing processes across modalities and tasks.