Biomedical subjects

R Yakushijin

Publications and source records attributed to R Yakushijin.

3 recordsLinked to original sources

PubMed2000

[Statistical efficiency of depth discrimination in stereoscopically overlapped and step-edge patterns].

We compared observers' statistical efficiencies of depth discrimination for two stereoscopic patterns: an overlapped pattern where two planes are overlapped at different depths, and a step-edge pattern where two planes are arranged side by side. In both patterns, elements in one plane were differentiated from those in the other plane by color (red vs. green) or orientation (45 deg vs. -45 deg). In the experiment, subjects were required to determine which plane was in front when Gaussian disparity noise was added to both of the elements' disparity values. The results showed that efficiencies were the same level for both patterns when the elements were differentiated by color. On the other hand, efficiencies were lower for the overlapped pattern than the step-edge pattern when the elements were differentiated by orientation regardless of the set size of elements. The patterns which we used were so sparse that the differences between the color and orientation conditions should arise from the process after matching.

Color Perception↗

PubMed1999

Does symmetry structure facilitate the depth separation between stereoscopically overlapped dot planes?

In the present study, we dealt with the problem of whether a symmetrical structure can influence the discrimination of the depth separation of overlapped dot planes. We investigated this problem with the use of both direct and indirect methods. In the direct method, we presented three or two overlapped dot planes consisting of symmetrical or random dots. The subjects were required to discriminate three overlapped from two overlapped planes. In the indirect method, the subjects were required to discriminate the depth positions of a target dot (or a pair of dots) that disappeared during stimulus presentation. Our results, obtained in three experiments, showed that the discrimination performance improved and reached a perfect level in the direct method and a modest plateau level in the indirect method with increasing relative disparity between the two outer planes, irrespective of whether the dot pattern had a symmetrical structure or not. These results suggest that a detection process for symmetry structure on a two-dimensional plane in three-dimensional space will not have a direct or an indirect connection (e.g., via a feedback loop) to a process involved in the depth separation.

Adult↗

PubMed1996

[Processing of asymmetrical noise in two- and three-dimensional global symmetry].

We investigated how the visual system processes asymmetrical noise in globally symmetrical patterns, and how much noise the visual system needs to discriminate between the perfectly symmetrical and imperfectly symmetrical patterns. Two experiments were carried out in which subjects were required to discriminate between the above patterns. This task was equivalent to a kind of the visual search task because subjects had to search for some targets asymmetrical dot pairs in two-dimensional (Experiment 1) or in three-dimensional mirror symmetry of dot patterns (Experiment 2). The results showed that the visual system processes noise largely in parallel in the two-dimensional symmetry, but largely in serial in the three-dimensional symmetry. In addition, analyses of the percent correct data suggested that the mechanism involved in detecting both the two- and three-dimensional symmetries in activated even by the patterns with a small amount of noise.

Adult↗