The effect of testing method on stereoanomaly

Previous tests of stereoanomaly (a deficit in stereopsis for a given disparity direction, crossed or uncrossed) have employed stimuli in which physical contours are presented with large disparities at exposure durations too brief for eye movements. This study investigated stereoanomaly using alternative testing methods with two types of stimuli: (1) stereoscopic contours formed from dynamic random-element stereograms presented both briefly and continuously, and (2) afterimages of retinally disparate physical contours. The results from three experiments show that most subjects who are classified as stereoanomalous under conditions of brief exposure perform normally under conditions that allow long inspection periods while eliminating eye movements. These results suggest that anomalies in stereopsis previously reported may depend on the method of testing rather than on deficits in underlying neural mechanisms.