Abstract
Distinct regions of posterior neocortex show reliable fMRI activation to images of objects and places (including buildings), respectively. What is not known is whether these regions are sensitive only to the geometry and surface cues defining the object and place stimuli, or whether the implied size and/or distance of those stimuli also matters. Regions of interest that responded primarily to images of places, faces, and small objects were determined with localizer fMRI scans. Participants then performed an oddball-detection task while viewing images of small objects (cameras) and buildings (garages) in different contexts: against a blank background (no size/distance cues other than those implied by the object's form); in the foreground of a simple size/depth illusion (implied small/close); and in the background of the illusion (implied large/far). Even though retinal size and eccentricity of the stimuli were equal in all conditions, activity in a ‘place’ ROI corresponding to the parahippocampal place area (PPA) was increased in the large/far conditions, relative to both the near/close and the blank background conditions. Conversely, activity in an ‘object’ ROI (lateral occipital area, LO) was increased in the near/close conditions. Both PPA and LO also showed category specificity. A more posterior place ROI (in the collateral sulcus) did not show the same effects of the size/distance manipulation as the PPA but was driven primarily by image category. his study clarifies the nature of the processing within higher-level visual areas by revealing the relative strengths of category and size/distance effects in different functional areas.
MG and SK supported by CIHR