THE EXPERIMENTAL technics and psychophysical methods utilized in the testing of binocular distance discrimination are not new developments; many features are to be found in standard texts. The present exposition is an attempt at a closer integration of certain elements of physiology with those of psychophysical methods, by which it is believed that greater significance may be obtained for both. A brief statement of the problem will first be made, and then those points significantly affected by the present outlook or procedure will be expanded.
The customary method of measuring distance discrimination is to present two objects, such as vertical rods, which may be made to differ in distance from the observer. These are seen through an aperture in a screen, thereby excluding certain cues. Nevertheless, the exclusion of cues other than retinal disparity or binocular parallax is by no means as complete as is often imagined; the size cue,