Research ReportThe role of apparent size in building- and object-specific regions of ventral visual cortex

Images of buildings and manipulable objects have been found to activate distinct regions in the ventral visual pathway. Yet, many non-categorical properties distinguish buildings from common everyday objects, and perhaps the most salient of these is size. In this fMRI study, we investigated whether or not changes in perceived scale can account for some of the differences in category-specific responses, independent of the influence of semantic or retinotopic image properties. We used independent scans to localize object-specific ROIs in lateral occipital cortex (LO) and scene-specific ROIs in the parahippocampal place area (PPA) and posterior collateral sulcus. We then contrasted the effects of stimulus category and perceived size/distance in these regions in a factorial design. Participants performed an oddball detection task while viewing images of objects, buildings, and planar rectangles both with and without a background that indicated stimulus size/distance via simple pictorial cues. The analyses of fMRI responses showed effects of perceived size/distance in addition to effects of category in LO and the PPA. Interestingly, when simple rectangles were presented in a control condition against the background that indicated size/distance, LO in the right hemisphere responded significantly more to the small/close rectangles than to the large/far ones, in spite of the fact that the rectangles themselves were identical. These findings suggest that ventral stream regions that show category specificity are modulated by the perceived size and distance of visual stimuli.

Research Highlights►Small perceived size amplified LO responses to otherwise non-preferred stimuli (buildings). ►Right hemisphere LO responded preferentially to geometric shapes when they were perceived to have the size of a small object. ►PPA showed independent preferences for semantic category (buildings) and for perceived size (large). ►The perceived size manipulation generally produced statistically larger effects than did semantic category.