Content-Independent Pointers Mediate Working Memory Storage for Both Visual and Verbal Stimuli.

Prominent models of working memory (WM) have long argued that visual and verbal WM rely on distinct storage buffers. Although this claim has been bolstered by both behavioral and neural studies that reveal important differences between visual and verbal storage in WM, recent work has also provided neural evidence for a domain-general signature of WM storage that is independent of the specific content stored. Our working hypothesis is that this content-independent load activity tracks the deployment of a "pointer" operation that supports contextual binding of the stored items. Here, we provide evidence that this pointer signal generalizes between simple colors and meaningful words. Across three data sets, including a reanalysis of previously published data and two novel EEG experiments, we demonstrate that multivariate EEG patterns track the number of items regardless of whether stimuli are visual (colored rectangles), verbal (letters or words), or conjunctions of both (colored words). Our findings demonstrate a robust load signal that remains stable across changes in perceptual format and stimulus type and is distinct from neural signals tracking spatial attention and cognitive effort. Critically, this pointer signal was observed in parallel with distinct EEG activity that tracked the stored content, suggesting a dissociation between the item-based indexing of stored items and the maintenance of their features.