Similarity Between Upright and Inverted Faces in a Yes/No Procedure: The Face Recognition Invariance

A 180° transformation in face orientation from the study stage to the test stage in a yes/no procedure reduces face recognition. Recognition of an upright face in the study and test stages (up-right–upright [UU] group) is better than in any other groups (upright–inverted [UI], IU, and II). In contrast to these findings, we report a phenomenon wherein the same pattern of face recognition is obtained in all four groups (UI, UU, IU, and II), which we call face recognition invariance. This can be explained by the hypothesis of visual similarity between an inverted face and an upright face, not by the hypothesis of mental rotation from inverted face to upright face. Visual similarity is based on certain elements that are mutual to 2 faces and elements that differentiate them. These mutual and differentiating elements resist the transformation of inversion (a 180° transformation) and can therefore be considered symmetric or salient components of the face, such as round eyes or thick lips. Hence, the similarity between inverted face and upright face is an important factor in explaining the effect of inversion on face recognition.