SSVEPs reveal dynamic (re-)allocation of spatial attention during maintenance and utilization of visual working memory

Visual Working Memory (VWM) allows to store goal-relevant information to guide future behaviour. Prior work suggests that VWM is spatially organized and relies on spatial attention directed towards locations at which memory items were encoded, even if location is task irrelevant. Importantly, attention often needs to be dynamically redistributed between locations, e.g., in preparation for an upcoming probe. Very little is known about how attentional resources are distributed between multiple locations during a VWM task and even less about the dynamic changes governing such attentional shifts over time. This is largely due to the inability to use behavioural outcomes to reveal fast dynamic changes within trials. We here demonstrate EEG Steady-State Visual Evoked Potentials (SSVEPs) to successfully track the dynamic allocation of spatial attention during a VWM task. Participants were presented with to-be-memorized gratings and distractors at two distinct locations, tagged with flickering discs. This allowed us to dynamically track attention allocated to memory and distractor items via their coupling with space by quantifying the amplitude and coherence of SSVEP responses in the EEG signal to flickering stimuli at the former memory and distractor locations. SSVEP responses did not differ between memory and distractor locations during early maintenance. However, shortly before probe comparison, we observed a decrease in SSVEP coherence over distractor locations indicative of a reallocation of spatial attentional resources. Reaction times were shorter when preceded by stronger decreases in SSVEP coherence at distractor locations, likely reflecting attentional shifts from the distractor to the probe or memory location.