Impaired configural processing for other-race faces revealed by the Thatcher illusion

The Thatcher illusion, where participants perceive upright faces with inverted eyes and mouth as grotesque but are markedly impaired in detecting grotesqueness when the entire faces are inverted, is commonly interpreted as reflecting disrupted configural and/or holistic processing in inverted faces. Previous research has suggested that other-race faces may be processed with a comparatively reduced reliance on configural (and more featural) information than own-race faces. The own-race bias refers to the tendency to recognise faces from a more familiar morphological group - mostly the own 'race' - faster and with higher accuracy than faces from less familiar groups. The present study tried to identify differences in processing own- and other-race faces (Thatcherised or not) across seven orientations ranging from 0° to 180° in 30° steps. For own-race faces, reaction times (RTs) to Thatcherised stimuli descriptively followed a sigmoidal function with a marked increase around 120° rotation, reflecting a typical reduced efficiency of configural processing once faces were rotated by more than 90°. For other-race faces, RTs increased more gradually and approximately linearly across orientations, consistent with reliance on featural processing. Accuracy was lowest for Thatcherised other-race faces with a steep decline starting between 30° and 60° of rotation. Overall, the results suggest a processing advantage for own-race faces that may rely more strongly on configural processing, whereas other-race faces appear to be processed with comparatively greater reliance on feature-based strategies.