During viewing of most objects in one's everyday environment, the binocular and monocular relative depth cues interact in a harmonious, concordant and reinforcing manner to provide perceptual stability. However, when one views pictorial art, these binocular and monocular cues are discordant, and thus a perceptual “cue conflict” arises. This acts to reduce the relative apparent perceived distance of objects in a painting, thus producing overall perceptual depth “flattening.” The theory and physiology underlying this phenomenon are discussed.