Perception of head orientation

There are two visual components to gaze: head orientation and orientation o f the eyes relative to the head. This study explores the accuracy with whic h subjects can discriminate head orientation when the eyes are centered in the head. Discrimination thresholds averaged 1.9 degrees of head rotation f or base head orientations of 0 degrees and 15 degrees, bur discrimination w as markedly poorer around a 30 degrees head orientation. Results were indep endent of spatial frequency and size over a 4-fold range. Neither negative contrast nor head inversion affected discrimination; Experiments dissociati ng the internal features from head outline revealed the presence of two mai n cues to discrimination: deviation of the head profile from bilateral symm etry, and deviation of nose orientation from vertical. Simulations show tha t model V4 units revealed in previous experiments with Glass patterns can e xtract the relevant head orientation information. The data are consistent w ith neurological data indicating a selective loss of face recognition in pr osopagnosia with spared gaze discrimination. (C) 2000 Elsevier Science Ltd. All rights reserved.