Abstract
Whether Japanese macaques can discriminate male from female conspecifics was investigated using color photographs of faces. Each trial began with the presentation of two photographs, one male and one female, on the monitor. Five different pairs of male-female photographs were used. Pairs were never mixed-i. e., a particular male photograph and a particular female photograph defined the stimulus pair. If the subjects touched the male photograph first and the female photograph second, they received a food reward. Selected photographs disappeared. In Experiment 1, the subjects learned to select five different male-female pairs in the male-first-female-second order, indicating that the subjects can discriminate the photographs of their conspecifics. In Experiment 2, the photographs displayed in Experiment 1 were again displayed, but the male-female photograph pairs were not fixed as in Experiment 1. Any of a total of 25 different male-female pairs could be displayed. The subjects selected the male photographs first and the female photographs second in any male-female pair. In Experiment 3, six novel photographs of conspecifics' faces (three males and three females) were added to 10 familiar photographs. The procedure was otherwise the same as in Experiment 2. It was found that when novel photographs were presented with the familiar female photographs, performance was not disrupted, however, when familiar female photographs were replaced with the novel male or female photographs, performance was disrupted.
