Abstract
T'he equidistance tendency is the tendency for objects or other inhomogeneities in the field of view to appear at the some dis- tance as each other with the strength of this tendency being inversely related to directional separation. The evidence for the existence of the equidistance tendency and for its ability to modify the perceived del)th resulting from size or stereos- copic cues is reviewed.The equidistance tendency is discussed as a disturbing factor in visual expermentation and as a necessary factor in the understnading of Emmert's law, the moon illusion and simular phenomena. Several possible explanations for the equidistnace tendency are evaluated briefly in terms of the range of phenomena with which it is identified.