Rhythms are fundamental to perception and action, structuring sensory input and enabling the brain to anticipate future events. Rhythm-based temporal expectations have often been explained by entrainment of neural oscillations to rhythmic sensory input, a mechanism most naturally suited to strictly periodic rhythms. However, it remains unclear whether this mechanism extends to expectations based on aperiodic, yet predictable, rhythms. Most previous studies have conflated predictability and periodicity by comparing isochronous (periodic and predictable) sequences to random (aperiodic and unpredictable) sequences. This work presents three empirical studies that combine behavioral measures with electroencephalography (EEG) to delineate predictability and periodicity, thereby providing a deeper understanding of the mechanisms underlying rhythm-based temporal expectations.
The results indicate that the brain can form temporal expectations for both periodic and aperiodic rhythms, yet it employs distinct mechanisms related to predictability and periodicity. Paper I showed that predictability, irrespective of periodicity, broadly enhances perceptual sensitivity, target-evoked P3b amplitudes, and preparatory neural activity (contingent negative variation; CNV), whereas phase-locked fluctuations in perceptual sensitivity and P3b amplitude appear to be optimal for periodic structures. Paper II expanded on this by revealing that beta-band oscillations (∼20 Hz) track temporal predictability, yet the functional link between pre-target beta power and behavioral performance is stronger for periodicity. Finally, Paper III demonstrated that auditory–motor synchronization improves temporal expectations beyond periodic rhythms but fails when the tempo accelerates, a shortfall likely explained by movement-related latency shifts in expectations towards the end of temporal sequences. Furthermore, event-related potential (ERP) results indicated increased task demands when adding movement, particularly for accelerating rhythms.
Together, these findings suggest that predictability drives general preparatory processes (as reflected in CNV and beta alignment) and benefits from synchronized movement, whereas periodicity may confer additional temporal precision that can fine-tune attentional gain and strengthen the behavioral relevance of beta power. This evidence indicates that rhythm-based facilitation involves more than simple oscillatory entrainment, and demonstrates an interplay between predictive processes and motor engagement. This work reveals that distinct neural mechanisms support different aspects of rhythm-based temporal expectation, which may explain why the benefits of rhythm for perception and action are often so context-dependent.