Abstract

Recent studies measuring the facial expressions of emotion have focused primarily on the perception of frontal
face images. As we frequently encounter expressive faces from different viewing angles, having a mechanism
which allows invariant expression perception would be advantageous to our social interactions. Although a
couple of studies have indicated comparable expression categorization accuracy across viewpoints, it is unknown
how perceived expression intensity and associated gaze behaviour change across viewing angles. Differences
could arise because diagnostic cues from local facial features for decoding expressions could vary with
viewpoints. Here we manipulated orientation of faces (frontal, mid-profile, and profile view) displaying six
common facial expressions of emotion, and measured participants' expression categorization accuracy, perceived
expression intensity and associated gaze patterns. In comparisonwith frontal faces, profile faces slightly reduced
identification rates for disgust and sad expressions, but significantly decreased perceived intensity for all tested
expressions. Although quantitatively viewpoint had expression-specific influence on the proportion of fixations
directed at local facial features, the qualitative gaze distribution within facial features (e.g., the eyes tended to
attract the highest proportion of fixations, followed by the nose and then the mouth region) was independent
of viewpoint and expression type. Our results suggest that the viewpoint-invariant facial expression processing
is categorical perception, which could be linked to a viewpoint-invariant holistic gaze strategy for extracting
expressive facial cues.