Tapping force variability influences temporal precision in paced finger tapping

The ideas about the origins and role of motor variability have been revised in recent years after realizing that a strictly peripheral origin is not sufficient to explain many observed aspects of brain function. Among these, time processing is emerging as one of the least studied functions where motor variability might have a critical role. Time processing in the range of hundreds of milliseconds includes the phenomenon of sensorimotor synchronization (SMS), where both sensory and motor timing processes play in parallel, likely overlapping in time. The most common and simple task to study SMS is paced finger tapping, where a person taps in synchrony with a periodic sequence of brief stimuli as in keeping pace with music. The main observable is the asynchrony, that is the time difference between every response and the corresponding stimulus along the sequence. Here we report that the variability of asynchronies in a paced finger-tapping experiment (N = 44) is correlated with the variability of the tapping force such that participants with smaller force variability have a better timing precision—but only in the absence of auditory feedback from the taps. We explain our observation by describing a potential mechanism based on empirical and theoretical results that bridges the gap between timing variability and force variability. Our results suggest that the tactile feedback in the presence of auditory feedback is mostly irrelevant in the perceptual determination of the occurrence time of the tap.