Supplementary material from "The neural basis of ideological differences in race categorization"

Multiracial individuals are often categorized as members of their ‘socially subordinate’ racial group—a form of social discrimination termed hypodescent—with political conservatives more likely than liberals to show this bias. Although hypodescent has been linked to racial hierarchy preservation motives, it remains unclear how political ideology influences categorization: Do conservatives and liberals see, feel or think about mixed-race faces differently? Do they differ in sensitivity to Black prototypicality (i.e. skin tone darkness and Afrocentric features) or racial ambiguity (i.e. categorization difficulty) of Black/White mixed-race faces? To help answer these questions, we collected a politically diverse sample of White participants and had them categorize mixed-race faces as Black or White during functional neuroimaging. We found that conservatism was related to greater anterior insula activity to racially ambiguous faces, and this pattern of brain activation mediated conservatives' use of hypodescent. This demonstrates that conservatives' greater sensitivity to racial ambiguity (rather than Black prototypicality) gives rise to greater categorization of mixed-race individuals into the socially subordinate group and tentatively suggests that conservatives may differ from liberals in their affective reactions to mixed-race faces. Implications for the study of race categorization and political psychology are discussed. This article is part of the theme issue ‘The political brain: neurocognitive and computational mechanisms'.