Abstract
Experimentation was undertaken to demonstrate that the depth acuity for panel test objects is complex and can be considered to be a combination of the acuities for monocular or congruent and binocular or disparate stimulation. Probability addition to combine the two contributing acuities produced a reasonable fit of the empirical data. A generalization to the natural environment of the trigonometric relation of the acuity for the alignment of horizontal edges to the acuity for depth was not consistent with results reported in the literature. A concept of equivalent-parallactic-angle acuity was offered in conjunction with the known improvement in acuity with reduction in angular separation of the acuity objects as an explanation of the reported improvement in stereoscopic acuity with distance. In contradistinction to implications in the literature, this research indicates that stereoscopic vision remains as the indicator of depth relations after cues available in monocular vision have ceased to be effective, if situational factors favoring the utility of monocular vision are controlled.

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