ABSTRACT
Lightness constancy can break down when an object is specially illuminated so that the light source is concealed and no light at all falls on the background. Familiarity with the size of an object, for example, will enable the reader to judge distance based on retinal size and known size, and the range of distances over which size constancy operates is larger in adults than in children since, presumably, their experience is less extensive. However, looking down from a high building the people do tend to see tiny people and tiny vehicles since the people lack of familiarity with vertical distance cues hampers the constancy mechanism. Visual constancies have been used to provide explanations for a range of visual illusions. In fact, no single perceptual mechanism can satisfactorily explain visual illusions, and it is likely that they arise from the interaction of a variety of processes at different levels of the visual system.
