Occlusion contributes to temporal processing differences between crossed and uncrossed stereopsis in random-dot displays

Stereoscopic depth discrimination was investigated in crossed and uncrossed directions using stimuli defined by binocular disparity differences embedd ed in dynamic random-dot stereograms. Across three experiments, fixation wa s directed to a point on the display screen (which placed crossed stimuli i n front of, and uncrossed stimuli behind, the background dots of the stereo gram), to a point in front of the display screen (which placed both crossed and uncrossed stimuli in front of the background dots), and to a point beh ind the display screen (which placed both crossed and uncrossed stimuli beh ind the background dots). Results showed that depth discrimination was alwa ys good when the stimuli appeared in front of the background dots of the st ereogram, whereas discrimination was always poor when the stimuli appeared behind the background dots. These results suggest that differences. between crossed and uncrossed stereopsis as reported in past research arose, in pa rt, from effects related to occlusion. (C) 1998 Elsevier Science Ltd. All r ights reserved.