A longitudinal investigation of chimpanzees' understanding of visual perception

Seven chimpanzees were tested for their understanding of the intentional as pect of visual perception at 5-6 years of age and again at 7 years of age. They appeared not to understand that they should use a species-typical, vis ually based begging gesture in front of someone who could see them, as oppo sed to someone who could not. Four experiments that were conducted when the se same subjects were adolescents are reported here. The results suggest th at there was no development between 5 and 9 years of age in the animals' un derstanding of visual perception as an internal state of attention. The sub jects appeared to learn procedural, stimulus-based rules related to the fro ntal orientation, the face, and the eyes of the experimenters. Even subject s most adept at these tasks appeared to rely on stimulus-based rule structu res, not an attribution of "seeing.".