Abstract
Because of the contradictory evidence as to whether stereoscopic acuity varies with observation distance, this study was undertaken to investigate the problem, with the utmost care being taken to maintain constant experimental conditions and to eliminate empirical clues to depth perception. By means of a haploscopic apparatus, which allowed careful control of all parameters, the stereoscopic acuity of three subjects with full accommodation was determined, in prolonged experiments for seven observation distances from 6 M. to 40 cm. Standard psychophysical methods were used. The results indicated, that stereoscopic acuity remains essentially constant, at least for observation distances beyond 50 cm. For one subject there was no change in stereoscopic acuity in distances from 6 M. to 40 cm. Two subjects showed essentially no change from 6 M. to 50 cm., but they did show a small decrease at the test distance of 40 cm. It was found also that controlling pupil size was unnecessary with a constant level of adapting luminance of about 50 millilamberts.