A phase-based mechanism of attentional selection in the auditory system

Perceptual targets are often easier to detect and process if they occur at a predictable time. This perceptual benefit of temporal predictability suggests that neural resources are allocated to specific moments predicted to be most informative, or away from those predicted to be distracting. The sensitivity to sensory information changes with the phase of neural oscillations. An alignment of oscillatory phase according to the predicted time and relevance of expected events has therefore been proposed as a mechanism underlying attentional selection. This hypothesis predicts that opposite phases are aligned to relevant and distracting events so that the former are amplified and the latter suppressed, but such an effect remained to be demonstrated. We presented 25 human participants with acoustic stimuli that occurred at a predictable or unpredictable time during a pitch-discrimination task. Temporal predictability did not only lead to faster reaction times, but it also aligned the phase of beta oscillations in the electroencephalogram (EEG) in anticipation of the stimulus. Crucially, the aligned phase was opposite, depending on whether the stimulus was relevant or a distractor for the task. Single-trial deviations from the mean aligned phases slowed down behavioural responses, demonstrating functional significance of the observed neural effects. All effects occurred in the absence of rhythmic stimulation, an important but rarely tested criterion to rule out spurious phase alignment from preceding events in a stimulus sequence. We therefore conclude that the alignment of oscillatory phase underlies the selection of sensory information in time. We speculate that beta oscillations allocate neural resources in networks comprising auditory and sensorimotor regions to the expected time of auditory information, facilitating behavioural responses to upcoming events.