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Abstract:
Purpose:How do observers recognize objects despite dramatic image variations that arise from changes in illumination? Some evidence suggests that changes in illumination direction influence object recognition (Kersten et al., ARVO 1995). We examine whether illumination dependency extends to face recognition. A corollary issue is whether cast shadows improve performance by providing information about light source direction, or hinder performance by introducing spurious edges that must be discounted prior to recognition. Methods:The 3-D geometry and color texture maps of 80 human faces were digitized using a 3-D laser scanner (Cyberware™). Each face was rendered with the light source located in the upper right or upper left quadrant in front of the face, and with cast shadows present or absent. On each trial, 2 faces were presented sequentially, each followed by a mask (a random array of face features). The two faces were illuminated from either the same or different directions. Observers judged whether the two faces were the same or different individuals. Half of the observers viewed faces with cast shadows, and half viewed faces without cast shadows. Results:When there was no change in the direction of illumination, recognition was faster (877 vs. 930 ms, p<.001) and more accurate (92% vs. 85%, p<.001) than when there was a change. Recognition was slower when cast shadows were present than when they were absent (973 vs. 833 ms, p<.05). Conclusions:Our finding that face recognition is illumination dependent is consistent with the use of "information-rich" representations for recognition. The results indicate that 1) face recognition processes are sensitive to either the direction of lighting or the resultant pattern of shading, and 2) rather than aiding recognition by providing information about the illuminant, cast shadows hinder recognition, possibly by masking out informative features or leading to spurious contours.
