Note on Stereoscopic Acuity and Observation Distance*

Abstract

Stereoscopic thresholds were determined for viewing distances of 0.5 meter and 10 meters in an instrument which essentially eliminates empirical factors to visual depth discrimination. The results with three observers show that there is no change in stereoscopic acuity at these two distances. On the basis of this result, data from a particular experiment reported in the literature which seemed to show an increase in stereoscopic acuity with increase in viewing distance were examined. It is shown that the results obtained might be better explained entirely on the basis of an empirical factor that depends upon the least perceptible difference in the angular sizes of two test objects of equal size and form set at different distances.