natural scenes abundantly contain local variations in luminance that facilitate figure-ground segregation. However, these first-order cues often introduce ambiguities and make figure-ground segregation a difficult task (Marr 1982). For example, shadows introduce false luminance boundaries that do not correspond to objects' boundaries in a visual scene. However, our visual system is able to distinguish these false boundaries from real ones using other cues, including second-order information such as texture, contrast, color, or motion differences between an object and its background. Particularly, relative motion is a powerful cue that can break camouflage when an object and its background have similar luminance, color, and texture. It can be sufficient to support perception of shape and size of three-dimensional surfaces and for depth ordering (Rogers and Graham 1979; Regan 1989; Regan and Hamstra 1992). This cue arises from motion parallax generated by an observer's movement or from the exogenous movement of objects in a scene.
展开▼
