Dissecting the neural focus of attention reveals distinct processes for spatial attention and object-based storage in visual working memory

Working memory (WM) maintains relevant information in an accessible state, and is composed of an active focus of attention and passive offline storage. Here, we dissect the focus of attention by showing that distinct neural signals index the online storage of objects and sustained spatial attention. We recorded EEG activity during two tasks that employed identical stimulus displays while the relative demands for object storage and spatial attention varied. Across four experiments, we found dissociable delay-period signatures for an attention task (which only required spatial attention) and WM task (which invoked both spatial attention and object storage). Although both tasks required active maintenance of spatial information, only the WM task elicited robust contralateral delay activity that was sensitive to the number of items in the array. Thus, we argue that the focus of attention is maintained via the combined operation of distinct processes for covert spatial orienting and object-based storage.