In the past five years, photo-interpretation research (Zeidner 1961; Zeidner, et. al. 1961; Leibowitz and Sulzer, 1965) has cast some doubt upon the usefulness of stereoscopic devices in enhancing photo-interpreter performance. Such findings are surprising in view of the fact that most laboratory studies, as well as many other applied studies, have indicated that stereoscopic viewing conditions yield higher increments of performance than non-stereo viewing conditions (Ogle, 1959; Robinson, 1964; Woodworth and Schlosberg, 1954; Chubb, 1964; Gould, 1964; and Smith & Gould, 1964). It should also be noted that a Russian photo-interpretation study (Gamezo and Rubakhin, 1961) concluded that: "As can be seen, the development and active functioning of the (spatial) concepts considerably broadens the possibilities of stereoscopy. Practice in stereoscopic,examination of aerial photograptis, in its turn, contributes to the development of spatial concepts, the enrichment of the store of initial, conventionally schematized, images of the stereo-model type."