Abstract and Concrete Working Memory Information in Human Visual Cortex

Neural correlates of visuospatial working memory (WM) information have been found in frontal, parietal, and early visual areas, but the principles by which distributed WM storage is topographically organised remain subject to debate. Here, we used functional magnetic resonance imaging, representational geometry analysis, and vision models to examine the extent to which WM representations across the cortical hierarchy may differ in terms of visuospatial abstraction. During retro-cued WM maintenance of rotated real-world objects, we found robust encoding of the objects orientation in both parietal and occipital visual areas. The representational format of this encoding was independent of the objects physical appearance and was surprisingly invariant across areas, indicating a high level of visuospatial abstraction even in the early visual cortex. Interestingly, we also found evidence for an orthogonal, object-specific orientation representation within the same areas, likely reflecting the sample stimulis concrete visual appearance. The latter--but not the former--type of distributed representation emerged also in a contemporary vision model. Together, the findings indicate the widespread co-existence of abstract (generalised) and concrete-visual representations multiplexed within the same brain areas. In contrast, prototypical orientation biases emerged only in the parietal cortex, suggesting a distinction between generalisation and categorisation in WM abstraction.