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Abstract:
Coherent visual perception requires the integration of local elements into global shapes. However,
the involvement of the various visual areas in the integration of local features into global
shapes remains largely unknown.Event-related fMRI was used to test for local and global
mechanisms of shape processing in higher visual object related areas. We tested for responses
in the Fusiform Face Area (FFA) known to respond selectively to faces [1] and the Parahippocampal
Place Area (PPA) known to be involved in the analysis of spatial layout [2]. The
stimuli consisted of images of houses or faces (global shapes) rendered by smaller images of
stimuli from these categories (local shapes). We tested four conditions: a) global faces rendered
by local faces; b) global faces rendered by local houses; c) global houses rendered by local
faces and d) global houses rendered by local houses. Subjects were instructed to judge whether
global and local shapes where from the same or different categories. Our results showed strong
fMRI responses for global faces in the FFA and global houses in the PPA independent of the
stimulus category at the local level. Lower category specic responses to the local shapes were
observed when the global shapes were from a different category than the local shapes. Further
studies tested for fMRI responses at different stimulus scales and attentional shifts. Stronger
responses to the local faces in the FFA and local houses in the PPA were observed compared
to global faces and global houses. Our results suggest differential processing of global and
local shape information in category selective areas. Furthermore, attention and spatial scale
inuence the processing of local and global shape information.
