Brief adaptation leads to faster reaction times in a face search task

Adaptation to faces can strongly bias the perceived characteristics of subsequently seen faces, but has been found to have relatively weak effects on tasks such as face discrimination. We examined the impact of prior adaptation on the salience of face stimuli, by using a visual search task. Participants adapted for 12 seconds to grayscale images of Asian faces that slowly morphed between 3 different identities. To control for low-level aftereffects, the adaptor was shown at the center of the screen and was 1.25x larger than the test faces, which were arranged in a circle in the periphery. The test array included images of 5 Asian distractor faces and a 6th target face formed by morphing between a White and Asian face. Target salience was controlled by varying the morph level from 20% to 50% White in steps of 10%. In a second, 2-AFC discrimination task using 2-down 1-up staircases, we also measured discrimination thresholds for 3 reference faces that contained 100%, 75% and 50% of the Asian to White face morph, respectively. Prior adaptation to the Asian face images induced significant aftereffects, shifting the Asian-White category boundary in the morph toward the Asian direction. This adaptation also reduced reaction times for detecting the target face in the search task for all of the tested morph levels, but had minimal effect on discrimination thresholds or search accuracy. Our results provide evidence that face ethnicity adaptation heightens the salience of target faces that differ along the ethnicity dimension, potentially because the adaptation renormalizes the adapting ethnicity so that it appears more neutral and therefore less distinctive.