Understanding visual barriers: evidence for Level 1 perspective taking in an orang-utan, Pongo pygmaeus

An adult female orang-utan used an untutored series of physical manipulations to guide humans to food placed beyond her reach. Through a series of experiments that involved different visual occlusions, this orang-utan appeared to take into account humans' visual states when using them to retrieve inaccessible goals. These data suggest that she was able to use her experience with visual barriers to model the visual perspective of visually impaired humans in a manner similar to that of 2- to 3-year-old human children.