Attention modulates EEG spectral activity across serial positions

Electroencephalographic (EEG) activity has been associated with attentional processes such as task-irrelevant stimulus suppression and orienting. The aim of this study was to understand how spectral activity evolves as words are presented in a word list learning task and as multiple components of attention are engaged under multitasking demands. We recorded scalp EEG in a delayed free-recall task in which participants encoded common noun word lists either under full attention (encoding only) or divided attention (simultaneous target detection task). In the target detection task, participants pressed a response button when a word was paired with a target-colored square but not for words paired with a distractor-colored square (cue condition). Activity in the high gamma frequencies (50-100 Hz) decreased while alpha activity (8-12 Hz) increased throughout word list presentation (i.e., across serial positions), consistent with prior work demonstrating effects of cognitive load on EEG spectral power. Divided attention attenuated this change in gamma power across the list. Cue condition modulated alpha activity evenly across serial positions, with consistently lower power during target trials than distractor trials. Our findings suggest that frequency-specific characteristics of processing during list encoding may reflect multiple components of attention that vary over different time scales. Gamma frequencies capture the interactive effects of cognitive load and dual-task demands, while alpha power separately reflects gradual increases in cognitive load and momentary orienting.