Abstract
Laboratory studies with controlled stimuli have shown that adaptation to natural variations in faces can strongly bias natural categorical judgments of faces (e.g. of gender, ethnicity, or expression). We tested for signs of these adaptive adjustments outside the lab, to examine how adaptation might influence face perception in “real” natural environments. To assess this, we probed judgments of ethnic category (Caucasian vs. Japanese) in observers who were exposed to different face populations. Participants were newly arrived (< 1 week) exchange students from Japan and Caucasian students in Reno, NV. Stimuli were morphs between Japanese and Caucasian face images from the Matsumoto and Ekman neutral-expression set. Observers made forced-choice judgments of ethnicity, with the morph level varied in a staircase to determine their category boundary. Japanese and Caucasian students chose boundaries closer to their own categories, suggesting that observers are more sensitive to how stimuli differ from their individual category. To test whether these boundaries might adjust in a changed environment, we tested a second group of Japanese students who had been resident in the US from 18 to 72 months. The mean boundary for this group was intermediate to and significantly different from both the Caucasian and newly-arrived students. Individual boundaries were also positively correlated with their self-reports of time in the US and negatively correlated with their report of the percent of time they spent with their own ethnic group. These shifts are consistent with an adaptive change in face coding that renormalizes face perception according to the average set of faces observers are exposed to.