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

Using their previously demonstrated gaze-following abilities, juvenile chim panzees (and 3-year-old human children) were tested to determine if they in terpreted seeing as the mental state of attention. The studies tested predi ctions generated by a low-level model of chimpanzee gaze-following which as sumes that chimpanzees do not understand attention as an unobservable, inte rnal mental state, and a high-level model which assumes that they do. In Ex pts 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 w hole head toward the correct cup, or just looked with the eyes. In Expt 1 t hese rues were static, whereas in Expt 2 the experimenter actively moved hi s or her head and/or eyes back-and-forth form the subjects' faces to the co rrect cup as they were attempting to make their choice. Expt 3 validated th e logic of Expts 1 and 2 by demonstrating that 3-year-old human children re sponded in a manner predicted by the high-level model. The results of the e xperiments converged on supporting the predictions of the low-level model o f juvenile chimpanzees' understanding of seeing.