Facial displays are an important form of social communication in nonhu
man primates. Clues to the information conveyed by faces are the tempo
ral and spatial characteristics of ocular viewing patterns to facial i
mages. The present study compares viewing patterns of four rhesus monk
eys (Macaca mulatta) to a set of 1- and 3-sec video segments of conspe
cific facial displays, which included open-mouth threat, lip-smack, ya
wn, fear-grimace, and neutral profile. Both static and dynamic video i
mages were used. Static human faces displaying open-mouth threat, smil
e, and neutral gestures were also presented. Eye position was recorded
with a surgically implanted eye-coil. The relative perceptual salienc
e of the eyes, the midface, and the mouth across different expressive
gestures was determined by analyzing the number of eye movements assoc
iated with each feature during static and dynamic presentations. The r
esults indicate that motion does not significantly affect the viewing
patterns to expressive facial displays, and when given a choice, monke
ys spend a relatively large amount of time inspecting the face, especi
ally the eyes, as opposed to areas surrounding the face. The expressiv
e nature of the facial display also affected viewing patterns in that
threatening and fear-related displays evoked a pattern of viewing that
differed from that recorded during the presentation of submissive-rel
ated facial displays. From these results we conclude that (1) the most
important determinant of the visual inspection patterns of faces is t
he constellation of physiognomic features and their configuration, but
not facial motion, (2) the eyes are generally the most salient facial
feature, and (3) the agonistic or affiliative dimension of an express
ive facial display can be delineated on the basis of viewing patterns.