UC Irvine

Humans and parrots are, among animals, uniquely able to move in time with a musical beat—a capacity termed beat perception and synchronization (BPS). Both are also advanced vocal learners, which has led to the proposal that BPS emerged as a by-product of the neural machinery for complex vocal learning. This dissertation examines rhythmic auditory-motor entrainment across three experiments, asking both where this capacity comes from and whether perceiving a rhythm itself engages the motor system.The first experiment tested a behavioral prediction of this speech-origin account: if rhythmic synchronization is grounded in the speech system, the vocal system should be at least as good at it as a non-vocal effector. Participants synchronized to isochronous rhythms at varying rates by finger tapping or by tongue clicking, a supralaryngeal vocal effector. Tongue clicking was as consistent as finger tapping and, on average, more closely aligned to the beat, leaving the speech-origin premise intact.The second experiment mapped the neural substrate of the same comparison with fMRI, asking whether the two effectors are served by segregated circuits or by a shared component. Beyond the expected effector-specific regions, finger and tongue synchronization converged on common cortex, most notably the dorsal precentral speech area (dPCSA), an auditory-weighted region of the speech-coordination network. Because the task involved no pitch or laryngeal control, the engagement of the dPCSA suggests it is not modality-specific but multifunctional—an auditory-weighted region within the motor system that may act as a common node for auditory-motor synchronization across effectors.The third experiment turned from the effectors of synchronization to the mechanism of perception, testing the motor theory of rhythm—the claim that perceiving a rhythm depends on covertly simulating it motorically. Using a forward-entrainment paradigm, the auditory rhythm was removed and participants generated the rhythm by tapping, a design that predicts an at-least-as-strong perceptual after-effect if the motor system is its source. A subset of participants showed a modulation of the expected magnitude, but the enhancement predicted by the motor account was not observed, and the pattern was not consistently phase-aligned across participants; the results are therefore inconclusive, neither confirming nor excluding a motor contribution.Together, these experiments support a speech-based origin for rhythmic synchronization and reveal a shared, auditory-weighted cortical substrate for it across vocal and non-vocal effectors, while leaving open whether rhythm perception itself depends on motor simulation.