Investigations of mirror self-recognition (SR) in chimpanzees (Pan troglodytes) have had small samples and divergent methods. In Experiment 1, 105 chimpanzees (10 months to 40 years of age) were observed for signs of SR across 5 days of continuous mirror exposure. In Experiments 2 and 3, negative SR adult and adolescent chimpanzees were saturated with mirror exposure in efforts to facilitate SR and a longitudinal study was conducted with a number of young subjects. In Experiment 4, mark tests were administered to groups of positive SR, negative SR, and ambiguous SR subjects. In Experiment 5, we explored whether previous positive SR reports in young chimpanzees were artifacts of increased arousal during mirror exposure. Results suggest that SR typically emerges at 4.5-8 years of age, at the population level the capacity declines in adulthood, and in group settings SR typically occurs within minutes of a subject's exposure to a mirror.

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Using their previously demonstrated gaze-following abilities, juvenile chimpanzees (and 3-year-old human children) were tested to determine if they interpreted seeing as the mental state of attention. The studies tested predictions generated by a low-level model of chimpanzee gaze-following which assumes that chimpanzees do not understand attention as an unobservable, internal mental state, and a high-level model which assumes that they do. In Expts 1 and 2, chimpanzees were rst trained to respond to a cup to which an experimenter pointed, and then tested on probe trials to determine if they could respond correctly when the experimenter either oriented his or her whole head toward the correct cup, or just looked with the eyes. In Expt 1 these cues were static, whereas in Expt 2 the experimenter actively moved his or her head and/or eyes back-and-forth form the subjects' faces to the correct cup as they were attempting to make their choice. Expt 3 validated the logic of Expts 1 and 2 by demonstrating that 3-year-old human children responded in a manner predicted by the high-level model. The results of the experiments converged on supporting the predictions of the low-level model of juvenile chimpanzees' understanding of seeing.

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Mirror self-recognition in chimpanzees (Pan troglodytes) is typically delayed until 4 1/2-8 years of age. Also, species capable of mirror self-recognition may be capable of some forms of mental state attribution related to intentions and knowledge. Previous investigations of knowledge attribution by chimpanzees used adolescents and adults but did not explicitly test for self-recognition. We report an investigation of knowledge attribution in 6 young chimpanzees previously tested for self-recognition. Subjects were required to discriminate between a person who had seen where food was hidden and another person who had not. The results are consistent with the proposition that most chimpanzees younger than 4 1/2 years of age show neither mirror self-recognition nor knowledge attribution. The results are also consistent with the idea that, just as in humans, development of self-recognition in chimpanzees may precede development of knowledge attribution.