Decoding auditory working memory load from EEG alpha oscillations

Working memory (WM) enables temporary retention of task-relevant information for imminent use. Increases in visual WM load are accompanied by elevated contralateral delay activity (CDA), and EEG alpha-band power. While most WM research focuses on the visual domain, it remains unknown whether similar EEG responses also reflect WM load in the auditory domain. Using EEG, we set out to establish such neuro-markers of auditory WM load. Participants memorized the pitches of 1 to 4 pure tones presented to one ear, with 1 to 4 consistent distractor tones presented to the other ear. Behaviorally, auditory WM capacity plateaued between set-sizes two and three. Unlike for visual WM, auditory WM load was not reflected in lateralized EEG responses. This shows that the CDA is a vision-specific rather than domain-general neuro-marker of WM load. Applying multivariate pattern analyses on the delay activity revealed that auditory WM load is reflected in (mostly temporal) patterns of alpha-band oscillations. Surprisingly, a temporal generalization analysis revealed that the alpha patterns reflecting specific load conditions changed throughout the maintenance period (despite load being inherently constant), revealing dynamic coding of auditory WM load.