Castillo-Almazan, A. | bioRxiv Science

bioRxiv2025

Categorical rhythmic priors in macaques

Rhythmic ability is a universal aspect of human cultures and sets the basis for musical rhythm perception and synchronization. While humans can synchronize movements to complex rhythms, it is unclear whether this capability extends to our primate ancestors. In this study, we explore whether primates can synchronize to complex rhythms and acquire rhythmic representations with generalizability akin to humans. Using controlled behavioral experiments, we provide evidence that monkeys not only can synchronize to short-long or long-short rhythms but also learn representations that generalize across a wide range of rhythm ratios and total durations. These results indicate ability to flexibly represent ratios within a relative timing framework is not exclusive to humans, but it is also present in monkeys. In addition, the produced intervals show a bias towards rhythmic categories. Notably, in an iterative tapping task, macaques and humans showed large priors for isochrony and integer ratios (2:1, 3:1). These results demonstrate a common biological foundation for rhythm synchronization in primates, extending our understanding of the shared cognitive mechanisms between primates and humans, and highlight the enormous potential of using monkeys to study the neurophysiological basis of complex rhythm perception.

neuroscience↗

bioRxiv2025

Flexible tapping synchronization in macaques: dynamic switching of timing strategies within rhythmic sequences

The ability to synchronize bodily movements with regular auditory rhythm across a broad range of tempos underlies humans capacity for playing music and dancing. This capability is prevalent across human cultures but relatively uncommon among non-human species. Recent research indicates that monkeys can predictively synchronize to regular, isochronous metronomes, exhibiting a preference for visual rather than auditory sequences. In this study, we trained macaques to perform a visual synchronization tapping task, testing their synchronization abilities over a wide tempo range and characterizing their precision and accuracy in timing intervals throughout rhythmic sequences. Additionally, we investigated whether the macaques employed priors or error correction strategies to maintain synchrony with the metronome. Our findings demonstrate that, following sufficient training, macaques exhibit a remarkable capability to synchronize across diverse tempos. Through an inference model analysis, we identified two distinct timing control strategies used by the macaques: an initial strong regression-to-the-mean effect transitioning dynamically into a more precise error correction approach at their preferred tempo. These results provide compelling evidence that primates possess sophisticated rhythmic timing mechanisms, effectively leveraging internal and external cues to regulate their tapping behavior according to task demands. NEW & NOTEWORTHYWe trained macaques in a visual synchronization tapping task and using an inference model we found that they are highly precise and accurate in their rhythmic performance. The model also captured a dynamic switch in behavior. At the beginning of the task, the monkeys used their prior knowledge about the interval statistics and then switched to an error correction mechanism to generate intervals depending on the previously produced duration.

neuroscience↗