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Roberto Caldara, Luca Vizioli; The Speed of Race. Journal of Vision 2010;10(7):699. doi: 10.1167/10.7.699.
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© ARVO (1962-2015); The Authors (2016-present)
Race is a universal, socially constructed concept used to categorize humans originating from different geographical locations by salient physiognomic variations (i.e., skin tone, eye shape, etc.). Race is extracted quickly and effectively from faces and, interestingly, such visual categorization impacts upon face processing performance. Humans are noticeably better at recognizing faces from the same- compared to other-racial groups: the so-called other-race effect. This well-established phenomenon is paired with an intriguing paradox: a faster categorization by race of other-race faces. Yet, the visual information and the cortical correlates driving this speed categorization advantage for race remain unknown. To this end, we combined a parametric psychophysical approach with electrophysiological signals recorded from Westerners and Easterners observers performing face categorization by race. We removed external features and normalized the amplitude-spectra, luminance and contrast of all the faces to control for potential confounds that could arise from trivial physiognomic differences between faces of different races. Importantly, we also manipulated the quantity of information available for race categorization, by using a linear phase interpolation technique with 11 phase noise levels, ranging from 20% to 70% in 5% increments (see supplementary figure). Consistent with current knowledge, race did not modulate the face sensitive N170 component with 60% phase signals or above. Strikingly, however, other-race faces containing weak phase signals were categorized more accurately and induced larger amplitudes differences on the N170 (arising at 40%, peaking at 50%) in both groups of observers. In contrast, same-race faces showed gradual accuracy and gradual N170 sensitivity to the quantity of phase signal, suggesting a more effective coding of information. Our findings show early categorical perception of race in the visual cortex, allowing a speed advantage to the detriment of fine-grained information coding. The very early detection of race could relate to biologically relevant mechanisms that shape human social interactions.
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