Scene representations in the parahippocampal place area are viewpoint-specific

Abstract

Parahippocampal cortex has been strongly implicated in the processing of visuospatial information. For example, fMRI studies have demonstrated that the “parahippocampal place area” (PPA) responds significantly more strongly to visual stimuli that convey information about surrounding space (e.g. pictures of scenes and houses) than to stimuli that do not (e.g. pictures of faces and objects). However, many questions about the nature of the underlying representations in the PPA are unanswered, including the critical question of whether the PPA represents scenes in egocentric or allocentric spatial coordinates. We used an event-related fMRI adaptation paradigm to examine this issue. Subjects viewed events consisting of two successively-presented tabletop scenes which could have three possible relationships to each other: (1) they could be the same scene but containing different objects; (2) they could be the same scene shown from different viewpoints (egocentric-only spatial change); (3) they could be different scenes but containing identical objects (egocentric+allocentric spatial change). Based on previous results, we expected that the regional event-related fMRI response to each scene-pair would be greater if the two scenes differed along an informational dimension processed by the region than if they did not. The PPA response to egocentric-only spatial changes was equal to the response to egocentric+allocentric spatial changes. In contrast, response in the fusiform face area (FFA) and lateral occipital complex (LO) to object changes was greater than response to either kind of spatial change. These results demonstrate that (1) scene representations in the PPA are viewpoint-specific; (2) the PPA and more lateral fusiform regions such as the FFA and LO are differentially involved in processing spatial vs. object information within a visual scene.