Neural correlates of subordinate-level categorization of own- and other-race faces in infancy.

Perceptual narrowing is a domain-general process in which infants move from a broad sensitivity to a wide range of stimuli to developing expertise within often experienced native stimuli (Maurer & Werker, 2014). One outcome of this is the own-race bias, characterized by an increasing difficulty in discriminating other-race faces with age and experience for those raised in a racially homogenous environment (Anzures, Quinn, Pascalis, Slater, Tanaka, & Lee, 2013). Theorists have proposed that this is due to a categorization-individuation process, wherein infants begin to categorize non-native stimuli but continue to individuate native stimuli (Hugenberg, Young, Bernstein, & Sacco, 2010; Nelson, 2001). Exposure to multiple exemplars during initial learning has been found to facilitate infant categorization of other-species faces while exposure to a single exemplar does not (Dixon, Reynolds, Romano, Roth, Stumpe, Guy, & Mosteller, 2019). The goal of this study was to investigate the effects of initial learning conditions on infants' ability to individuate and categorize own- and other-race faces. Ten-month-old infants were familiarized with a single exemplar or multiple exemplars of own- or other-race faces. Event-related potentials (ERPs) were recorded while infants were presented with the familiar face(s) they were exposed to during familiarization, novel faces from the same race used during familiarization, and novel faces from a race other than the one used in familiarization. Infants familiarized with a single exemplar, regardless of race, showed significant differences in both the Nc component (Negative central, associated with visual attention) and the LSW (late slow wave, associated with recognition memory) between familiar and novel faces at the subordinate-level category of race. No differences were found across familiarization conditions for the P400 component associated with face processing. Infants familiarized with multiple exemplars showed no evidence of discriminating faces at the categorical or individual level. Results suggest that, in contrast to other-species faces, infants at this age may process human faces more efficiently when familiarized with a single exemplar. The implications of the current findings are discussed in relation to the impact of initial learning conditions on infants' ability to individuate and categorize own- and other-species faces and social implications of infants' processing of other-race faces.