A phase based mechanism of stimulus anticipation in the auditory system

Recent theories of attentional selection propose that opposite oscillatory phases align to relevant and distracting events to amplify the former and suppress the latter, although this effect had not been demonstrated. We presented 25 human participants with acoustic stimuli occurring at predictable or unpredictable times during a pitch-discrimination task. Temporal predictability accelerated reaction times and aligned the phase of beta oscillations in the electroencephalogram (EEG) in stimulus anticipation. Crucially, aligned phases were opposite for relevant versus distracting stimuli, and phase opposition re-emerged before pitch discrimination. Single-trial deviations from mean aligned phases slowed down behavioural responses. Phase effects were accompanied by increased parieto-occipital alpha power temporally aligned to expected distractors. All effects occurred without rhythmic stimulation, ruling out spurious phase alignment from preceding events. We therefore show that oscillatory phase alignment underlies anticipation of sensory information in time. However, our results are more consistent with phase-based event encoding that facilitates subsequent behavioural responses, rather than with a mechanism of attentional selection.