Recent studies have revealed that items held in visual working memory (VWM) change their status depending on task-relevance. Here, we used steady-state visual evoked potentials (SSVEPs) to track the dynamics of these state changes during a combined visual search and working memory paradigm. Participants memorized two coloured items, followed by a cue that indicated which item needed to be searched for first (creating an attentional template for current task-relevant information) and which second (creating an accessory memory for later use). Peripheral checkerboards that matched the colors of the attentional template and accessory item as well as an irrelevant control color flickered at unique frequencies during a retention interval and the two searches, enabling the simultaneous tracking of both types of memory. We observed differences in occipital SSVEP amplitudes depending on the status (e.g. task-relevance) of the memory items. More specifically, the amplitude of the color matching the current attentional template was higher compared to the accessory and irrelevant colors during both the retention interval and the second search, indicating enhanced activation of the template. However, surprisingly, during the first search we did not find this enhancement of the template. A difference in cognitive demand between the two searches could underlie this difference. Taken together, we demonstrate that items held in VWM can adopt a different status depending on task-relevance and that SSVEPs provide a useful tool in studying these dynamics.
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