Sensitivity to spatiotopic location in the human visual system
56.457, Tuesday, 20-May, 2:45 pm - 6:45 pm, Banyan Breezeway
Yuval Porat1, Tanya Orlov1, Ayelet Mckyton1, Ehud Zohary1,2,3; 1Neurobiology Department, Life Sciences Institute, Hebrew University of Jerusalem, Jerusalem 91904, Israel, 2Interdisciplinary Center for Neural Computation, Hebrew University of Jerusalem, Jerusalem 91904, Israel, 3The Edmond & Lily Safra Center for Brain Sciences, Hebrew University of Jerusalem, Jerusalem 91904, Israel
Introduction: Visual information in the early visual processing stages is represented in strictly eye‐centered (retinotopic) coordinates. Thus, each eye movement, generating a different retinal image, evokes a different pattern of activity, although the visual scene is unaltered. Our perception, however, shows clear visual stability. This may indicate that non‐retinotopic representations (i.e. head, body or world-; termed ‘spatiotopic’) are invoked higher in the visual pathways. It is, however, unclear where in the brain and under what conditions such representations emerge. Methods: Subjects (N=13) participated in a block‐designed fMRI repetition suppression (RS) experiment. In each block, a series of identical or different objects appeared. Eye movements were made between stimulus presentations, such that objects were either in the same screen position (e.g spatiotopic) or in different positions (non-spatiopic). Spatiotopic and non-spatiotopic blocks were equated in terms of their distribution of retinal positions of the stimuli. Results: 2x2 ANOVA performed on the activation parameters revealed 3 different effects: regions along the LOS, OTG, ITG, and fusiform gyrus were sensitive to the identity of the object (i.e. an Identity RS). In contrast, parietal regions (aIPS, pIPS, and SPL) were differentially activated when stimuli appeared in the same spatiotopic position (spatiotopic-position RS). Finally, some regions (pFus, LOS and occipito-parietal junction) revealed an interaction effect: the identity RS was greater when objects appeared in the same spatiotopic location. Conclusion: Our results suggest that the spatiotopic location of objects (irrespective of their identity) is encoded in parietal cortex. Currently, it is unclear, if the spatiotopic-position RS was mainly due to the repetition at the same position, or prior knowledge of object position, as objects repeatedly appeared in the same screen location throughout the block. An ongoing event-related task design may elucidate the contribution of these factors to the emergence of spatiotopic representations in the visual system.