Dissociations and associations between shape and category representations in the two visual pathways

The dorsal and ventral visual pathways represent both visual and conceptual object properties. Yet the relative contribution of these two factors in the representational content of visual areas is unclear. Indeed, research investigating brain category representations rarely dissociate visual and semantic properties of objects. We present a human event-related fMRI study with a two-factorial stimulus set with 54 images that explicitly dissociates shape from category to investigate their independent contribution as well as their interactions through representational similarity analyses. Results reveal a contribution from each dimension in both streams, with a transition from shape to category along the posterior-to-anterior anatomical axis. The nature of category representations differs in the two pathways: ventral areas represent object animacy and dorsal areas represent object action properties. Furthermore, information about shape evolved from low-level pixel-based to high-level perceived shape following a posterior-to-anterior gradient similar to the shape-to-category emergence. To conclude, results show that representations of shape and category independently coexist, but at the same time they are closely related throughout the visual hierarchy.