Abstract
Face identification is a critical activity of daily living that may be impaired by blur or distortions caused by vision loss or prosopometamorphopsia. Distortions alter the spatial relationships among facial features, disrupting configural information. In this experiment, we examine how the spatial scale and amplitude of distortions affect the identification of upright faces, and, to examine the inversion effect, inverted faces. Bandpass filtered noise (Fpeak@1-32 cycles/face) was used to generate pixel shifts to distort calm and neutral faces from the IASLab database. The amplitude of distortion was varied using an adaptive staircase. 8 normally-sighted subjects were given unlimited time to identify which of 4 distorted faces matched the identity of an undistorted reference face, each presented in a 6.5°-9.8° ellipse in a 2*2 grid. Image cues were removed from each face by equalizing the luminance distribution and chrominance of the average face. There was a significant interaction between face orientation and distortion frequency (F5,35=4.5, p=0.003), where sensitivity as a function of distortion frequency monotonically increased for inverted faces but was U-shaped with a peak at 4-8 cycles/face for upright faces. A significant face inversion effect (p<0.05) was found when distortions were applied at the low and high distortion frequencies, but there was no significant inversion effect when distortions were applied at the middle critical frequencies (4-16 cycles/face). These results suggest that the face inversion effect for distortion is mediated by a narrow spatial band. The critical frequency is correlated with the distance between the eyes, consistent with a critical role for eye geometry in upright face identification.