Category and Space in the Ventral Stream

The experiments described in this thesis address the question of how category and space are represented in the brain. First, we asked whether object category is encoded in specialized modules or whether it is distributed throughout the ventral stream. To this means we conducted an fMRI adaptation experiment and tested whether face- and house-selective ventral stream areas exhibit adaptation across object categories. We found that both areas adapted to both preferred and non-preferred object stimuli, and the magnitude of the adaptation effect was higher for preferred categories. Our study favors a theory of a distributed processing of object information and undermines the notion of modules that exclusively encode one category. Second, we investigated the extent of space representation in ventral stream areas. We combined retinotopic mapping techniques with the presentation of object stimuli. We were able to demonstrate that the ventral stream areas FFA and PPA are highly space-sensitive and that the representation of space covers nearly the entire visual field. We found indications that spatial sensitivity is highest for the preferred category, indicating that the representations of category and of space interact. Furthermore, voxels that were more robustly sensitive to space were at the same time less sensitive to category membership, indicating a trade-off of sensitivity for category and space. Our studies shed new light on the functional properties of the ventral stream, as we have demonstrated that ventral stream areas are less specialized in object identity than previously thought, and instead perform additional computations on spatial aspects of visual stimuli.