Evoked and entrained pupillary activity while moving to preferred tempo and beyond

Abstract

People synchronize their movements more easily to rhythms with tempi that are closer to their preferred motor rates than with ones that are faster or slower. This has been explained in terms of dynamical systems theory where internal oscillators couple to external rhythms for more fluent processing; this coupling is more efficient the closer the external rhythms are to the preferred rates of the internal oscillators. Thus, this more efficient coupling at one’s preferred rate should be associated with lower cognitive demands and better attentional entrainment compared to faster or slower rates. We tested this by measuring participants’ pupil sizes, a proxy for noradrenergic attention, while either listening or synchronizing their finger taps to metronomes played at rates faster, slower, or at their preferred rate. We found that synchronizing (relative to listening) to the faster and slower metronomes evoked larger pupil sizes whereas there was no difference at participants’ preferred rate. In line with dynamical systems theory, these results demonstrate that synchronizing is more cognitively demanding than listening only at tempi beyond one’s preferred rate. Furthermore, pupillary phase coherence increased while synchronizing compared to listening to all three metronomes, indicating that synchronous movements resulted in more efficiently allocated attention. Beyond their theoretical implications, our findings suggest that rehabilitation for movement disorders should be tailored to patients’ preferred rates to reduce cognitive demands. Moreover, attention and developmental disorders may benefit from pupillary entrainment as a diagnostic tool in rhythmic- and movement-based interventions.