Individual neurophysiological signatures of spontaneous rhythm processing

Abstract

When sensory input conveys rhythmic regularity, we can form predictions about the timing of upcoming events. Although rhythm processing capacities differ considerably between individuals, these differences are often obscured by participant- and trial-level data averaging procedures in M/EEG research. Here, we systematically assessed the neurophysiological variability displayed by individuals listening to isochronous equitone sequences interspersed with unexpected deviant tones. We first focused on rhythm tracking and tested the anticipatory phase alignment of delta-band activity to expected tone onsets. These analyses confirmed that individuals encode temporal regularities and form temporal predictions, but highlight clear inter- and intra-participant variability. This observation may indicate individual and flexible tracking mechanisms, which show consistency at the single-trial level, but variability over trials. We then modelled single-trial time-locked neural responses in the beta-band to investigate individual tendencies to spontaneously employ binary grouping ("tic-toc effect"). This approach identified binary (strong-weak), ternary (strong-weak-weak), and mixed accentuation patterns, confirming the superimposition of a basic beat pattern. Furthermore, we characterized individual grouping preferences and tendencies to use binary, ternary, or combined patterns over trials. Importantly, the processing of standard and deviant tones was modulated by the employed pattern. The current approach supports individualized neurophysiological profiling as a sensitive strategy to identify dynamically evolving neural signatures of rhythm and beat processing. We further suggest that close examination of neurophysiological variability is critical to improve our understanding of the individual and flexible mechanisms underlying the capacities to rapidly evaluate and adapt to environmental rhythms. Significance statementFor decades, music, speech and rhythm research investigated how humans process, predict, and adapt to environmental rhythms. By adopting a single-trial and -participant approach, we avert the common pooling of EEG data in favor of individual time-varying neural signatures of rhythm tracking and beat processing. The results highlight large inter- and intra-individual differences in rhythm tracking, arguing against the typically documented phase-specificity for entrainment. On top of that, we characterize individual variability in beat processing, by showing that binary, ternary and other accentuation patterns are used over time, and ultimately affect the processing of (un-)expected auditory events. The approach aids individual neural profiling and may therefore allow identifying altered neural activity and its consequences in natural listening contexts.