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Long Sha, Ming Meng; The timing of categorical face perception. Journal of Vision 2010;10(7):676. doi: 10.1167/10.7.676.
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© ARVO (1962-2015); The Authors (2016-present)
The visual system's ability to organize the world into distinct object classes manifests itself in categorical perceptual judgments – two patterns with very similar low-level attributes might nevertheless be perceived as members of different categories and hence as very distinct objects. Previous studies in our lab have investigated neural correlates of categorization in the domain of faces (Meng et al., VSS, 2008). We collected a set of natural images that spanned a range of facial similarity from non-faces to genuine faces. By using fMRI, neural response patterns in the left fusiform gyrus were found to change in a graded fashion as the stimuli became increasingly face-like, while those in the right fusiform showed a step-like profile corresponding to a categorical difference between faces and non-faces. An important question that arises from these results concerns the functional dependencies between the graded analyses of the left fusiform gyrus and the categorical analyses of the right. To address this question, we tested the timing of categorical face perception. Subjects viewed each image for either a brief duration or unlimited duration and categorized the image as a face or non-face. When the duration was brief, false face report gradually increased as a function dependent on face likeness of the stimulus image. In contrast, when the presentation duration was unlimited, subject's report revealed a sharp, step-like categorical boundary. These results suggest that categorical face perception requires substantial processing time. Image-level facial similarity analyses may precede categorization. Taken together with previous neuroimaging results, we will discuss possible functional relationships between the graded analyses of the left fusiform gyrus and the categorical analyses of the right.
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