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Michal Bernstein, Jonathan Oron, Boaz Sadeh, Galit Yovel; Effects of grouping on neural competition in object category selective cortex. Journal of Vision 2013;13(9):175. doi: 10.1167/13.9.175.
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Single-cell electrophysiological studies have shown that multiple stimuli presented simultaneously in the cell’s receptive field compete for representation by mutually suppressing neural responses. Suppressive interactions among multiple stimuli have been also reported in fMRI studies that showed lower fMRI signal to simultaneously presented stimuli than to the same stimuli presented sequentially. These fMRI studies have so far examined such competition effect only for low-level stimuli (e.g. gabor patches). In the present study we examined neural competition among high-level visual stimuli (i.e., faces and bodies) in object category selective cortex to answer the following questions: Does neural competition in object category selective cortex exist? Is competition reduced for two objects that can be grouped to a single object (i.e. a face above a body)? To that end, we presented pairs of faces and headless bodies above and below fixation simultaneously or sequentially. Subjects performed a fixation task so the two stimuli were unattended. Our results show significant competition effect between two faces presented simultaneously in the face-selective areas, and between two bodies presented simultaneously in the body-selective areas. Interestingly, neural competition was markedly reduced when a face was presented above a body, generating the perception of a person, but not when a body was presented above a face. This effect was larger in ventral temporal than in lateral occipital face and body areas. Our findings show that neural competition between multiple object stimuli in object category selective cortex exists. They also show that competition in object-selective areas occurs between objects, and not between features within an object, therefore, once stimuli are grouped together, they are perceived as a unit rather than two competing stimuli, and neural competition is reduced.
Meeting abstract presented at VSS 2013
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