Perceived intrinsic 3D shape of faces is robust to changes in lighting direction, image rotation and polarity inversion

Face recognition from 2D images is influenced by various factors, including lighting conditions, viewing direction, rotation, and polarity inversion. It has been proposed that these techniques affect face recognition by distorting shape from shading. This study investigates the perception of 3D face shape in 2D images using a gauge figure task. Two experiments were conducted where participants adjusted a gauge figure across multiple locations within a 3D image to assess its surface structure. We manipulated face orientation, lighting direction, and polarity inversion (exp 2). While these manipulations resulted in variations from the true surface structure, they could be explained by an affine transformation. This suggests that the perception of the intrinsic 3D shape of faces is stable across these image manipulation techniques. The effects of viewing conditions on face recognition may thus be better interpreted through their influence on the perception of material properties such as pigmentation, or on information closer to the level of the retinal image itself.

Contrast Negation Impairs Sorting Unfamiliar Faces by Identity: A Comparison With Original (Contrast-Positive) and Stretched Images

Recognition of unfamiliar faces is difficult in part due to variations in expressions, angles, and image quality. Studies suggest shape and surface properties play varied roles in face learning, and identification of unfamiliar faces uses diagnostic pigmentation/surface reflectance relative to shape information. Here, participants sorted photo-cards of unfamiliar faces by identity, which were shown in their original, stretched, and contrast-negated forms, to examine the utility of diagnostic shape and surface properties in sorting unfamiliar faces by identity. In four experiments, we varied the presentation order of conditions (contrast-negated first or original first with stretched second across experiments) and whether the same or different photo-cards were seen across conditions. Stretching the images did not impair performance in any measures relative to other conditions. Contrast negation generally exacerbated poor sorting by identity compared with the other conditions. However, seeing the contrast-negated photo-cards last mitigated some of the effects of contrast negation. Together, results suggest an important role for surface properties such as pigmentation and reflectance for sorting by identity and add to literatures on informational content and appearance variability in discrimination of facial identity.

Discrimination and recognition of faces with changed configuration

Subtle metric differences in facial configuration, such as between-person variation in the distances between the eyes, have been used widely in psychology to explain face recognition. However, these studies of configuration have typically utilized unfamiliar faces rather than the familiar faces that the process of recognition ultimately seeks to explain. This study investigates whether face recognition relies on the metric information presumed in configural theory, by manipulating the interocular distance in both unfamiliar and familiar faces. In Experiment 1, observers were asked to detect which face in a pair was presented with its configuration intact. In Experiment 2, this discrimination task was repeated with faces presented individually, and observers were also asked to make familiarity categorizations to the same stimuli. In both experiments, familiarity determined detection of faces in their original configuration, and also enhanced identity categorization in Experiment 2. However, discrimination of configuration was generally low. In turn, recognition accuracy was generally high irrespective of configuration condition. Moreover, observers most sensitive to configuration during discrimination did not appear to rely on this information for recognition of familiar faces. These results demonstrate that configuration theory provides limited explanatory power for the recognition of familiar faces.