ABSTRACT Stereoscopic depth was measured in central vision under photopic viewing conditions. Two test lines, one appearing above the other, were briefly exposed and adjusted to match in apparent depth. The standard deviation of the subject's settings provided the depth threshold. Log threshold increased roughly linearly with increasing disparity. The exponential rise in depth threshold with increasing disparity was thus verified. Previous authors working under mesopic conditions and at great peripheral angles, found a steeper increase in depth threshold as a function of disparity for the more central angles. The present results showed that the stereoscopic response behaves differently under photopic conditions and peripheral angles up to 1.3 deg arc, as the slopes of the straight lines fitting the data sets from different angles within central vision were not found significantly different. Subjective depth equality settings resulted in physical equality for small disparities, and stereoscopic matching can therefore be performed with great veridicality. But for greater disparities, an anisometric relation between retinal areas above and below the horizontal meridian became apparent.
Sturla Krekling (Sun,) studied this question.