Experience With Face Groups Impacts Face Processing, but Not Face Differentiation in 6- and 9-Month-Old Infants.

The present study examined neural differentiation of faces from familiar and unfamiliar race groups at 6 and 9 months of age. Two of four face groups (one familiar and one unfamiliar) were shown to infants based on parent reports of infant face experience. Infants completed a fast periodic visual stimulation (FPVS) EEG task in which separate blocks of familiar and unfamiliar face groups, equated for low-level visual differences, were presented at a rate of 6 Hz. Within each block, a different individual was presented at 1.2 Hz (every fifth face). A medial occipital 6 Hz neural response was greater for faces from the familiar compared to the unfamiliar group, which was primarily driven by the 6-month-old age group. A robust occipital 1.2 Hz response was present for both ages and for both familiar and unfamiliar face groups, suggesting individual-level face differentiation. However, the topography of the 1.2 Hz response differed for 6- and 9-month-olds and suggests that face differentiation becomes increasingly right lateralized with age. The present results highlight the importance of face experience on visuocortical brain responses associated with face processing (6 Hz) and suggest that face differentiation (1.2 Hz) is present by 6 months of age and not impacted by face familiarity.