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Abstract:
Background: To survive in a dynamically changing world, our brain constantly predicts the timing of future events. Rhythmic temporal structure is a potent cue for temporal predictions, such that processing of events is facilitated when they coincide with rhythmic input (i.e. appear on-beat), even for task-irrelevant rhythms. Mechanistically, the CNV, a slow premotor preparatory brain potential, is incidentally driven by rhythms such that it peaks at on-beat times. We tested the potency of rhythms as temporal cues by presenting targets with high probability between visual rhythmic stimuli (i.e. off-beat). This made off-beat moments task-relevant and encouraged observers to intentionally shift attention to them, while ignoring on-beat moments. In another condition, on-beat moments were task-relevant and off-beat moments were irrelevant. Results: When the time of the off-beat targets was jittered, the CNV peaked at on-beat times, which also showed behavioral benefit. However, when the time of the off-beat targets was fixed relative to rhythmic stimuli, responses were faster to off-beat targets compared to on-beat. Crucially, this was accompanied by modulation of the CNV trajectory such that it peaked at the task-relevant times and not at on-beat times. Finally, post-target brain activity demonstrated a sustained positivity for on-beat relative to off-beat targets, starting from 100 ms after target onset, while task-relevance only affected the later N2 ERP. Conclusions: Our findings imply that what seems to be an automatic effect of rhythms can be overcome given sufficient temporal information. This stands in contrast to prevalent entrainment models of temporal predictions, which explain rhythmic temporal predictions by synchronization of slow brain activity to the rhythmicity. Further, the dissociation we find in post-target responses extends the understanding of the unintentional and intentional components of temporal expectation formation in rhythmic environments.
