An investigation of the difference in stereoacuity between crossed and uncrossed disparities using Frisby and TNO tests.

Is stereoacuity better, on average, with a crossed test disparity? To answer this question, 15 subjects with good stereoacuity performed Frisby and TNO stereotests with test plates in each of 2 possible orientations, crossed and uncrossed. Stereoacuities and response times were measured. The answer was that a subject's stereoacuity with crossed and uncrossed disparity could be different, e.g., 30 and 480 sec arc, respectively, but that, on average, a crossed disparity was no easier to detect than an uncrossed one. There were more and greater differences with the TNO than with the Frisby test and Frisby stereoacuity was, on the average, 4 times better. It is recommended that tests which can have two orientations be tested in both and the best result taken as the stereoacuity.