Is there a linear or a nonlinear relationship between rotation and configural processing of faces?

Research suggests that inverted faces are harder to recognise than upright faces because of a disruption in processing their configural properties. Reasons for this difficulty were explored by investigating people's ability to identify faces at intermediate angles of rotation. Participants were asked to discriminate blurred famous and unfamiliar faces presented at nine angles. Blurred faces were used to minimise featural processing strategies, and to assess the effects of rotation that are specific to configural processing. The results indicate a linear relationship between angle of rotation and recognition accuracy. It appears that configural processing becomes gradually more disrupted the further a face is oriented away from the upright. The implications of these findings for competing explanations of the face-inversion effect are discussed.