Constancy

An important function of perceptual systems is to accurately determine object properties—physical properties of objects that remain constant. For example, an object's shape, size, and reflectance (fraction of light and spectral distribution of light reflected from the object) typically remain constant and so are considered properties of the object. Examples of object properties (with the object properties italicized) are a brown cat, a six-foot-tall person, a rectangular door. Perceptual constancy refers to the perception of these object properties as remaining constant even when things such as illumination, distance, and viewing angle cause changes in the stimulation these objects present to the receptors. For example, as a rectangular door swings open, the image it casts on the retina changes from rectangular, when the door is viewed ...