Measurement of the ability in monocular depth perception during gazing at near visual target-effect of the ocular parallax cue

Abstract

We analyze contributions of monocular cues for depth perception during observing at near distance. We experimented on the depth ordering task between two target bars under some conditions, which provided few monocular depth cues. First, a subject judged on the relative depth between two bars through a pinhole. A pinhole makes the accommodative effect less. However, the percentage of correct answer on depth ordering is higher than chance-level. Next, we added a condition, which was changing of the target bars' thickness randomly. It makes size constancy invalid. In this case, for some subjects, the percentage of correct answer fell off. If the subjects are given a suggestion of it, some subjects can recover high correct rates, but others can't. We tried to evaluate these results by a /spl chi//sup 2/ test. From the results, it implies that a quite different factor from conventional ones provides the depth cue. Even under such a severe condition, humans can shift a sight line. So, we infer that it is the effect of an ocular parallax cue. On the other hand, it shows that size constancy is a strong factor for some persons, so they can't use an ocular parallax cue. Nevertheless, it seems that ocular parallax has a possibility as a monocular depth cue if we are aware of the factor.