Abstract
Attention can be directed by not only the external environment but also internal representations held in visual working memory (VWM). The former is known to sample environmental information in a relatively discrete manner, whether this manner is also at play within the latter, however, remains unclear. Here, we performed both the behavioral dense-sampling and high-density electroencephalogram (EEG) experiments to examine this issue. Subjects in both experiments were asked to perform a classical VWM-guided task with two items held in VWM either simultaneously (Experiment 1) or consecutively (Experiment 2). In both Experiments 1 and 2, behavioral results showed that items held in VWM were not continuous but alternated with each other and underwent a theta-band (4-7 Hz) rhythmic fluctuation over time. In other words, the items held in VWM were prioritized in alternation, not simultaneously, to guide our attention. EEG results further showed that the alpha-band oscillation of prioritizing (cued) and suppressing (non-cued) items alternations continued during the memory retention phase, and the amplitude of this alpha-band was significantly correlated with subjects’ behavioral performance. More importantly, the alpha-band oscillation on both posterior sides had significant phase coupling with the theta-band oscillation in prefrontal regions, and the coupling intensity was also leading alternately in a theta-band (4Hz). Altogether, our results suggest that memory is essentially processing multiple objects alternately in time, rather than continuously entangling a single object. In addition, our results also suggest that posterior alpha-band oscillations underlie the flexible activation and deactivation of VWM representations and that prefrontal theta-band oscillations play a key role in the executive control of this process.