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Ming Meng, Tharian Cherian, Gaurav Singal, Pawan Sinha; Functional lateralization of face processing. Journal of Vision 2010;10(7):562. doi: https://doi.org/10.1167/10.7.562.
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Several fMRI researchers have noted that face induced brain activity is more reliably localized in the right fusiform gyrus than in the left. However, we lack a precise characterization of the hemispheric differences in facial selectivity. Identifying the nature of these functional asymmetries is crucial for understanding the organization of face processing in the human brain. To address this need, we undertook a three pronged approach: 1. We compared brain activation in the left and right fusiform gyri induced by a set of natural images that span a range of facial similarity from random non-faces to genuine faces. 2. We measured the modulatory influence of contextual information on brain activation patterns. 3. We evaluated the temporal dynamics of face processing in the left and right fusiform gyri using a rapid event-related design. Results on all three fronts have revealed interesting hemispheric differences. Specifically, we found that: 1. Activation patterns in the left fusiform gyrus correlate with image level face-semblance, while those in the right correlate with categorical face/non-face judgments. 2. Contextual information transforms graded responses in the left fusiform to categorical ones, but does not qualitatively change the responses in the right. 3. Graded pattern analyses in the left occur earlier than categorical analyses in the right fusiform. Contextual modulation too is evident earlier in the left than in the right. Furthermore, face-selectivity persists in the right even after activity in the left has returned to baseline. These results provide important clues regarding the functional architecture of face processing. They are consistent with the notion that the left hemisphere is involved in rapid processing of ‘low-level’ face semblance, and perhaps a precursor to categorical analyses in the right (cf. Rossion, et al., 2000; de Gelder & Rouw, 2001; Miller, Kingstone, & Gazzaniga, 2002).
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