Temporal and spatiotemporal perturbations in paced finger tapping point to a common mechanism for the processing of time errors

Paced finger tapping is a sensorimotor synchronization task where a subject is instructed to keep pace with an external metronome, as when following along with the beat of music, and the time differences (asynchronies) between each stimulus and its response are recorded. The usual way to study the underlying error correction mechanism is to make unexpected temporal perturbations to the stimuli sequence and then let the subject recover average synchronization. A critical but overlooked issue in traditional temporal perturbations, however, is that at the moment of perturbation two things change: both the stimuli period (a parameter) and the asynchrony (a variable). In terms of experimental manipulation, it would be desirable to have separate, independent control of parameter and variable values. In this work we perform paced finger tapping experiments combining simple temporal perturbations (tempo step change) and spatial perturbations with temporal effect (raised or lowered point of contact). In this way we decouple the parameter-and-variable confounding of traditional temporal perturbations and perform novel perturbations where either the parameter only changes or the variable only changes. Our results show nonlinear features like asymmetry and are compatible with the idea of a common mechanism for the correction of all types of asynchronies. We suggest taking this confounding into account when analyzing perturbations of any kind in finger tapping tasks but also in other areas of sensorimotor synchronization, like music performance experiments and paced walking in gait coordination studies.