Visual working memory enhances neural representations of matching visual input

Visual information that is actively maintained in working memory has been shown to affect concurrent perception. One possible explanation is that working memory and sensory representations embody a common neural substrate. Here, we hypothesized that visual information maintained in working memory should enhance concurrent processing of visual input that matches the content of working memory. To test this hypothesis, 15 participants performed a delayed match to sample task during fMRI scanning. Participants were sequentially presented with two central shape stimuli, drawn from three shape categories (rectangles, ellipses and triangles), and a postcue. The postcue indicated which of the two shapes should be memorized for subsequent recall. During the retention interval a different shape was presented that either matched the category of the cued (memorized) shape or the uncued shape, or was of the hitherto unused shape category. This task-irrelevant shape stimulus was presented peripherally for one second at an unpredictable delay and location. The results revealed that those brain areas that responded to the occurrence of the shape stimulus per se (including parietal and ventral occipital cortex) showed increased activation when its shape category matched the memorized shape category, despite identical visual stimulation in mismatching trials. Next, we assessed whether the quality of the neural representation was modulated by the content of visual working memory as well. Multivariate pattern analysis allowed for decoding the shape category of the task-irrelevant shape stimulus when it matched, but not when it mismatched, the memorized shape category. Together, our results demonstrate enhanced visual processing of stimuli that match the content of working memory. This enhanced response might underlie a plethora of well-known behavioral phenomena, such as the finding that visual input that matches rather than mismatches the content of visual working memory attracts attention and eye movements, and gains preferential access to awareness.