1 RITMO Centre for Interdisciplinary Studies in Rhythm, Time and Motion, University of Oslo, Oslo, Norway.
2 Department of Psychology, University of Oslo, Oslo, Norway.
3 Department of Psychology, Concordia University, Montreal, QC, Canada.
4 Montreal Centre for Brain, Music and Sound (BRAMS), Montreal, QC, Canada.
5 Centre for Research in Brain, Language and Music (CRBLM), Montreal, QC, Canada.
6 Department of Musicology, University of Oslo, Oslo, Norway.
7 Institut des Sciences du Sport Santé de Paris (I3SP), URP 3625, Université Paris Cité, Paris, France.

People synchronize their movements more easily to rhythms with tempi closer to their preferred motor rates than with faster or slower ones. More efficient coupling at one's preferred rate, compared to faster or slower rates, should be associated with lower cognitive demands and better attentional entrainment, as predicted by dynamical system theories of perception and action. We show that synchronizing one's finger taps to metronomes at tempi outside of their preferred rate evokes larger pupil sizes, a proxy for noradrenergic attention, relative to passively listening. This demonstrates that synchronizing is more cognitively demanding than listening only at tempi outside of one's preferred rate. Furthermore, pupillary phase coherence increased for all tempi while synchronizing compared to listening, 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.