Configural specificity of the lateral occipital cortex.
While regions of the lateral occipital cortex (LOC) are known to be selective for objects relative to feature-matched controls, it is not known what set of cues or configurations are used to promote this selectivity. Many theories of perceptual organization have emphasized the figure-ground relationship as being especially important in object-level processing. In the present work we studied the role of perceptual organization in eliciting visual evoked potentials from the object selective LOC. To do this, we used two-region stimuli in which the regions were modulated at different temporal frequencies and were comprised of either symmetric or asymmetric arrangements. The asymmetric arrangement produced an unambiguous figure-ground relationship consistent with a smaller figure region surrounded by a larger background, while four different symmetric arrangements resulted in ambiguous figure-ground relationships but still possessed strong kinetic boundaries between the regions. The surrounded figure-ground arrangement evoked greater activity in the LOC relative to first-tier visual areas (V1-V3). Response selectivity in the LOC, however, was not present for the four different types of symmetric stimuli. These results suggest that kinetic texture boundaries alone are not sufficient to trigger selective processing in the LOC, but that the spatial configuration of a figure that is surrounded by a larger background is both necessary and sufficient to selectively activate the LOC.
Appelbaum, LG; Ales, JM; Cottereau, B; Norcia, AM
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