The influence of eye and mouth position on judgments of face orientation

Abstract

This study investigated whether humans judge the orientation of a face based on the absolute or relative positions of features. The stimuli were schematic faces, consisting of an outer elliptical contour and either two eyes plus mouth (EM condition), or the eyes or mouth presented alone (E and M conditions). The eyes and mouth were located at five different heights within the outer contour. Eye and mouth height were combined factorially, yielding a total of 25 stimuli in the EM condition, and 5 stimuli in each of the E and M conditions. On each trial, a stimulus was presented for 250 ms and participants (n=16) judged whether the face was upright or inverted using a 4-point confidence scale. The EM, E, and M conditions were performed in different blocks. In the E condition, faces were judged upright whenever eye height was equal to or higher than the center of the face. In the M condition, faces were judged upright whenever mouth height was equal to or less than the center of the face. Upright judgments for faces with the feature (eyes or mouth) in the center of the face suggested an upright bias. In the EM condition, orientation judgments were influenced significantly by the relative heights of the eyes and mouth: faces were judged as upright whenever the eyes were higher than the mouth, even when both features were unnaturally located in the upper- or lower-half of the face. In summary, human judgments of face orientation were based on both the absolute and relative positions of eyes and mouths, and there was a bias to perceive faces as upright.

Footnotes

 This study is supported by the CIHR-JSPS Japan-Canada Joint Health Research Program and the Canada Research Chair programme.