Abstract
Although alpha oscillations (8-13 Hz) are thought to play a role in suppressing distractions when just one sensory modality is being attended, are the same neural mechanisms involved when attention is being paid to multiple sensory modalities? For an answer, I examined cortical oscillations while human subjects divided attention between auditory and visual sequences. In Experiment 1, subjects performed an oddball task with auditory, visual, or simultaneous audiovisual sequences in separate blocks, while the electroencephalogram was recorded using high-density scalp electrodes. Continuous alpha oscillations over posterior regions, observed when subjects attempt to attend to auditory sequences in particular, suggest that the brain may suppress processing of distracting visual surroundings in order to advantage auditory processing. During a divided-attention audio-visual condition, an oddball (a rare and unusual stimulus) could occur in either the auditory or the visual domain, requiring that attention be divided between modalities. Fronto-central theta band (4-7 Hz) activity was strongest in this audiovisual condition. Given that theta-band activity has been associated with both attention and short-term memory, Experiment 2 sought to differentiate these possible roles of fronto-central theta activity during multisensory divided attention. Using a modified version of the oddball task from Experiment 1, Experiment 2 showed that differences in theta power among conditions were independent of short-term memory load. Ruling out theta’s association with short-term memory, I conclude that fronto-central theta activity is likely a marker of multisensory divided attention.