Context Binding in Visual Working Memory Is Reflected in Bilateral Event-Related Potentials, But Not in Contralateral Delay Activity.

Successful retrieval of a specific item from visual working memory (VWM) depends on the binding of that item to its unique context. Recent functional magnetic resonance imaging studies of VWM manipulating memory set homogeneity have identified an important role for the intraparietal sulcus in context binding, independent of any role in representing stimulus identity. The current study explored whether the contralateral delay activity (CDA), which is an event-related potential (ERP) component derived from posterior electrodes that tracks the amount of information held in VWM, might also be sensitive to context-binding demands. In experiment 1, human participants performed lateralized delayed recognition with memory sets containing one, three, or five items that were drawn from the same category (orientations: "homogeneous") or from different categories (orientation, color, and luminance: "heterogeneous"). Because the location and identity of the memory probe indicated the item to be retrieved, homogeneous trials placed higher context-binding demands. VWM capacity was higher in heterogeneous trials. ERPs contralateral (contra) and ipsilateral (ipsi) to the remembered stimuli were higher for homogeneous trials, but these differences were removed in the contra - ipsi subtraction that produced the CDA. In experiment 2, human participants performed lateralized delayed recall with memory sets of one or three items (homogeneous or heterogeneous). Behavior was superior for three-item heterogeneous trials than for homogeneous trials, with modeling revealing context-binding errors in the latter. Bilateral ERPs and CDA results replicated experiment 1. These results support that the CDA tracks the number of object files engaged by VWM and establish that it is not sensitive to context-binding demands.