Polyrhythm Perception and Production: A Scoping Review.

In music, rhythms can range from simple isochrony to complex polyrhythms, in which multiple nonharmonically related metrical hierarchies are superimposed (e.g., 2:3, 4:5). This scoping review synthesizes 64 studies comprising 96 experiments on polyrhythm perception and production. Over the past decades, research has shown that factors such as polyrhythm ratio, tempo, sensory modality, and musical training shape how we perceive and produce polyrhythms. Although most reviewed studies lack subjective measurements of polyrhythm complexity, behavioral tasks suggest that ratio sum (e.g., five in 2:3) and the Farey tree offer rough complexity estimates. While tempo affects which periodicity is perceived as the underlying beat, these effects are limited by the preference for binary subdivision grouping. Finally, the reviewed literature suggests that polyrhythms are more often perceived as integrated patterns than segregated streams. For future research, we recommend defining polyrhythms as the superposition of two or more nonharmonically related pulses that share a common cycle, and adding a clear description of whether these pulses are isochronous stimuli or perceived beats extracted from nonisochronous stimuli. Combining behavioral and subjective measures across different polyrhythmic contexts could clarify subjective complexity and under which circumstances polyrhythms are perceived and produced as integrated rhythms or segregated pulses.