Approaches to studying gaze monitoring in nonhuman primates.

Abstract

This thesis explored the gaze monitoring abilities of monkeys. A review of previous studies indicated that the face is a valuable source of information for nonhuman primates. When viewing faces, nonhuman primates can recognise conspecifics, individuals and emotional expressions. Within the face, the eyes are a particularly salient feature; nonhuman primates are extremely sensitive to the eyes and gaze is an integral component of all primate expressions. However, where another individual is looking potentially allows a primate access to a wealth of information about their environment; another’s visual orientation can indicate important objects or events. It is this informational value of gaze, rather than responses to self-directed gaze, that is the focus of this thesis. Previous research has indicated that nonhuman primates’ responses to gaze are fairly inconsistent across tasks. Therefore, the studies reported here explored monkeys’ responses to gaze within a number of experimental paradigms in order to better evaluate their abilities. Approaches included spontaneous responses to another individual’s visual co-orientation, picture discrimination, object-choice tasks, a competitive task and a computer-based cueing paradigm. The data reported in this thesis are consistent with previous research in this Held. Nonhuman primates spontaneously follow gaze within a simple visual co-orientation paradigm, but they do not readily use gaze as an informational cue within other paradigms, such as the object-choice task. Explanations of this pattern of results are suggested, and mainly focus on the ecological validity of the tasks and general procedural issues. In addition, nonhuman primates do not demonstrate preferential responding to eye gaze, in fact, head orientation seems to be the more salient cue. These findings are not readily accommodated by Baron-Cohen’s (1994) model that proposes that the eyes are the pre-eminent source of information regarding another individuals’ gaze direction. Directions for future research are identified. There is considerable need for further research on a wider range of primate species, and for a consideration o f the ontogeny of behaviours. A more detailed analysis o f the role o f gaze in nonhuman primates’ natural interactions is considered desirable and other paradigms are also suggested.