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.