Illumination effects in face recognition

How do observers recognize faces despite dramatic image variations that arise from changes in illumination? This paper examines 1) whether face recognition is sensitive to illumination direction, and 2) whether cast shadows improve performance by providing information about illumination, or hinder performance by introducing spurious edges. In Experiment 1, observers judged whether 2 sequentially-presented faces, illuminated from the same or different directions, were the same or different individuals. Cast shadows were present for half of the observers. Performance was impaired by a change in the illumination direction and by the presence of shadows. In Experiment 2, observers learned to name 8 faces under one illumination direction (left/right) and one cast-shadow condition (present/absent); they were later tested under novel illumination and shadow conditions. Performance declined for unfamiliar illumination directions, but not for unfamiliar shadow conditions. The finding that face recognition is illumination dependent is consistent with the use of image-based representations. The results indicate that face recognition processes are sensitive to either the direction of lighting or the resultant pattern of shading, and that cast shadows can hinder recognition, possibly by masking informative features or leading to spurious contours.