P1-21: A Study on Stereoanomalies: Comparison of Upper and Lower Visual Field

Stereoanomalies suggest that some people lack disparity detectors or have a disorder of the subsystem associated with stereopsis and consequently fail to perceive correct depth. Crossed and uncrossed disparity detectors are well-established mechanisms. The current study searches other stereoanomalies. In the experiment, a fixation and a test target were presented for 500 msec in a darkroom. The fixation was right in front of the subject, and the test was on the median plane. The test appeared at a upper or lower visual field with crossed or uncrossed disparity. The eccentricity of the position of the test target was 2, 4, or 6 deg. The given disparity was between the average threshold of depth percept and the average fusion limit; so observers with normal vision must percept them correctly. The task of the subject was to report the apparent depth of the test target: far, near, or zero. Some 14 subjects participated: 9 of these subjects gave no anomalous signs; 1 indicated defection of uncrossed disparity detection; 3 indicated defection of uncrossed disparity detection only at a lower visual field; 1 indicated defection of uncrossed disparity detection at a lower visual field and that of crossed disparity detection at an upper visual field. These results indicate that some people have stereoanomalies that depend on visual fields