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

Visual Working Memory (VWM) allows us to temporarily store goal-relevant information to guide future behavior. Prior work has established that VWM and spatial attention are intrinsically connected - even if location is irrelevant for responses: behavioral and neural correlates of attention show spatial biases, specific to the location at which memory items were encoded. This suggests that VWM is spatially organized and that maintaining information might rely on the allocation of spatial attention towards the location of memory items. Importantly, attention often needs to be dynamically redistributed between several 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 behavioral 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. During maintenance and retrieval, each location was tagged with a disk flickering at either 10 or 13 Hz. 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 at memory locations did not differ from distractor locations during early parts of the maintenance window. 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, reflecting the reallocation of attention from the distractor location to the memory location or towards the distinct upcoming probe location. Broader Significance We demonstrate that SSVEPs can inform about dynamic processes in VWM, even if location does not have to be reported by participants. This finding not only supports the notion of a spatially organized VWM, but also reveals that SSVEPs betray a dynamic prioritization process of working memory items and locations over time that is directly predictive of memory performance.