Visual Search for the Orientations of Faces by a Chimpanzee (Pan troglodytes)

Abstract

One female chimpanzee was tested on perception of orientation of faces using a visual search task. In Experiment 1, the subject showed better performance in the tasks in which the upright human faces were presented as a target or distractors than the task in which only the horizontal and inverted faces were presented. Furthermore, the subject responded faster when the upright face was the target than when the upright faces were distractors. This asymmetry was not evident when the horizontal and inverted faces were combined. Superiority in detecting the upright stimulus was also observed when the upright and horizontal chimpanzee faces were combined, but not when the stimuli were photographs of houses (Experiment 2). When each stimulus was different in identity from each other but the target could be identified on the basis of its orientation, the performance was not so severely impaired when the subject searched the upright faces of humans and chimpanzees. The subject showed difficulty in detecting the house target in this condition. It was suggested that the subject searched the upright faces after she had identified the stimuli as “faces”.