Perception of pictorial depth cues by pigeons

Pigeons were trained to discriminate pictures of intact objects from pictures of objects in which both depth from shading and depth from perspective cues were manipulated. Depth from shading was manipulated either by scrambling or by removing three-dimensional shading cues. Depth from perspective was manipulated either by presenting pictures of objects with a two-dimensional outline (i.e., a square) or with a three-dimensional outline (i.e., a cube). Transfer tests with novel images suggest that pigeons perceive and utilize both types of pictorial depth cues. The implications of these results for our understanding of picture perception in pigeons are discussed.