Revisiting the perception of upside-down faces.

In two experiments, the effect of orientation on face perception was assessed. Using a scale from 1 (normal) to 7 (bizarre), participants rated normal, unaltered faces and faces in which changes had been made to spatial-relational properties (eyes and mouth inverted or relative position of the eyes and mouth altered) or to component properties (eyes whitened and teeth blackened). For unaltered and component-distortion faces, bizarreness ratings increased linearly as orientation increased from 0 degree to 180 degrees. For spatial-distortion faces, a discontinuity in the function relating orientation and bizarreness was in evidence between 90 degrees and 120 degrees. The results provide support for the view that there is a qualitative difference in the processing of upright and inverted faces due to the disproportionate effect of inversion on the encoding of spatial-relational information.