Abstract
We report a series of experiments to investigate a novel fat face illusion: when two identical images of the same face are aligned vertically, the face at the bottom appears "fatter" than the top one. In Experiment 1, we showed this illusion to emerge only when the faces were presented upright, but not when inverted. In Experiment 2, a JND procedure revealed the size of the fat face illusion to be 4%. That is, the bottom face appeared to be 4% bigger than its actual size. In Experiment 3, clocks were shown in the same vertically aligned fashion as the faces but we failed to observe a similar illusion, suggesting that the fat illusion does not generalize to every category of canonically upright objects with similar geometric shape as a face. In Experiment 4, participants still reported a fat face illusion when observing the two identical vertically aligned upright faces with inverted eyes and mouth. However, a reverse fat illusion (the top face being fatter) emerged when the face was inverted but the eyes and mouth remained upright. These findings taken together demonstrated that the fat face illusion is influenced by both configural and featural information in a face, suggesting that this effect could not simply be explained as a special case of the Jastrow illusion (1891) because the latter is not sensitive to geometric shape orientation, or internal elements, or the relationship between internal elements and the geometric shape that encompasses them. Potential mechanisms of the fat face illusion and the implications for understanding face processing are discussed.
Meeting abstract presented at VSS 2012