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Abstract:
A common denominator in all vision tasks is scene segmentation: what is fore- and background, which visual components belong to the same or different entities? In prior studies we used a bi-stable stimulus that can either be perceived as separate local components or as a global Gestalt. fMRI and TMS showed that posterior parietal cortex (PPC) was selectively and causally involved in Gestalt perception. Here, we investigated the role of the PPC in resolving perceptual organization using three additional such asymmetric bistable stimuli. Importantly, all of these stimuli evoked a default lowlevel and a non-default high-level interpretation. The illusory interpretations involved high-level visual mechanisms like shape perception and motion integration. For all stimuli, we found an activity pattern that was highly similar for the contrast
of default (simple) vs. non-default (complex) perceptual
interpretations. It consistently and prominently involved
posterior parietal cortex. We also found for all stimuli strong early visual cortex deactivations during high-level perceptual interpretations. Mid-level regions such as LOC or motion regions were differentially involved with each stimulus class and percept-type. Our results suggest that PPC is not merely involved in grouping items into global Gestalt, but instead more generally it is involved in generating the more complex, high-level perceptual interpretation of a given stimulus. The activation of the PPC and the concurrent deactivation of early visual areas during high-level perceptual interpretations are in line with predictive models of visual perception. Our findings
suggest a generic mechanism for scene segmentation with the PPC as its anatomical substrate.
