Problems in depth perception: perceived size and distance of familiar objects. AM 66-22.

Familiar size is usually regarded as an important empirical cue determining the apparent distances of objects. The learning process that is assumed to occur in the development of this distance cue depends upon the relation between the retinal size of an object and its physical distance from the observer (0). A simple explanation of the process involved in this cue system is as follows. In a situation in which many cues are present to determine the perceived distance of the familiar object, 0 might be expected to learn to associate the retinal size of the familiar object with its perceived distance. As the result of many such associations involving the same familiar object at different distances, presumably 0 would perceive the familiar object as being at a particular distance from himself solely as a consequence of the presence of a particular retinal size. Clearly, such a learning process would be expected to result in a proportionality between the physical distance D and the perceived dis-tanceD' of the object from 0; i.e.,