Quantitative relations among vernier, real depth, and stereoscopic depth acuities.

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Abstract
Three visual discrimination situations were presented to 4 subjects. The situations were: vernier, real depth, and stereoscopic depth. In each situation the exptl. variable was the separation between the ends of 2 vertical rods used as test objects. Six separations varying from 3.6 " to 891" were used. The visual distance from the eye to the test object was 4622 mm. in all cases. Lighting conditions for all 3 situations were made as similar as possible. The psychophysical method of constant stimuli was employed, and the stimulus duration for each judgment was 4 sec. Thresholds for the vernier situation were the same for monocular and binocular conditions, varying from 1" to 7" in both cases. The stereoscopic thresholds were very slightly higher than the real depth thresholds, both ranging from 2 " to 5". The results are taken as evidence that the real depth and stereoscopic depth thresholds are essentially identical. It is also concluded that the depth thresholds are too low to be accounted for by the simple summation of monocular, vernier components.
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