Strategic control of location and ordinal context in visual working memory

Working memory requires encoding stimulus identity and context (e.g., where or when it was presented). To explore the neural bases of the strategic control of context binding in working memory, we acquired fMRI while subjects performed delayed recognition of three orientation patches presented serially and at different locations. The recognition probe was an orientation patch with a superimposed digit, and depending on pretrial instruction subjects responded according to the probe’s location (location-relevant), the ordinal position corresponding to its digit (order-relevant), or just its orientation (context-irrelevant). Delay-period signal in PPC was greater for context-relevant than for context-irrelevant trials, and multivariate decoding revealed strong sensitivity to context binding requirements (relevant vs. irrelevant) and to critical domain of context (location- vs. order-relevant) in both occipital cortex and PPC. At recognition, multivariate inverted encoding modeling revealed markedly different patterns in these two regions, suggesting different context-processing functions. In occipital cortex, an active representation of the location of each of the three samples was reinstated, regardless of trial type. The pattern in PPC, in contrast, suggested a filtering of location-context information that was dependent upon trial type. These results indicate that PPC exerts strategic control over the representation of location context in visual working memory.