Comprehension of seeing as a referential act in young children, but not juvenile chimpanzees

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 first 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 rues 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.