The inattentional rhythm in audition
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The detection of temporally unpredictable visual targets depends on the preceding phase of alpha oscillations (~7-12 Hz). In audition, however, such an effect seemed to be absent. Due to the transient nature of its input, the auditory system might be particularly vulnerable to information loss that occurs if relevant information coincides with the low excitability phase of the oscillation. We therefore hypothesised that effects of oscillatory phase in audition will be restored if auditory events are made task-irrelevant and information loss can be tolerated. To this end, we collected electroencephalography (EEG) data from 29 human participants (21F) while they detected pure tones at one sound frequency and ignored others. Confirming our hypothesis, we found that the neural response to task-irrelevant but not to task-relevant tones depends on the pre-stimulus phase of neural oscillations. Alpha oscillations modulated early stages of stimulus processing, whereas theta oscillations (~3-7 Hz) affected later components, possibly related to distractor inhibition. We also found evidence that alpha oscillations alternate between sound frequencies during divided attention. Together, our results suggest that the efficacy of auditory oscillations depends on the context they operate in, and demonstrate how they can be employed in a system that heavily relies on information unfolding over time.
Significance Statement
The phase of neural oscillations shapes visual processing, but such an effect seemed absent in the auditory system when confronted with temporally unpredictable events. We here provide evidence that oscillatory mechanisms in audition critically depend on the degree of possible information loss during the oscillation’s low excitability phase, possibly reflecting a mechanism to cope with the rapid sensory dynamics that audition is normally exposed to. We reach this conclusion by demonstrating that the processing of task-irrelevant but not task-relevant tones depends on the pre-stimulus phase of neural oscillations during selective attention. During divided attention, cycles of alpha oscillations seemed to alternate between possible acoustic targets similar to what was observed in vision, suggesting an attentional process that generalises across modalities.
