Abstract
Past research on aging and the perception of stereoscopic shape and depth (Norman, Dawson, & Butler, 2000; Norman, Crabtree, Herrmann, Thompson, Shular, & Clayton, in press) has found that while there is a quantitative effect of age, that the qualitative patterns of performances are essentially identical for younger and older adults. Many extant models of stereopsis are cooperative. The “pulling phenomenon” found by Julesz and Chang (1976) demonstrates the cooperative nature of stereopsis. The purpose of the current experiment was to use the methods of Julesz and Chang to determine whether and to what extent aging affects how well binocular disparity detectors interact within a cooperative network. Twenty observers (ten younger & ten older) viewed ambiguous random-dot stereograms that incorporated varying numbers of bias points with unambiguous disparity (0, 50, 250, 500, 1000, & 2000 bias points). Consistent with the earlier findings of Julesz and Chang, we found that a relatively small percentage of bias points (5.6 percent) was sufficient to “pull” the observers' stereoscopic percepts into an organization that was completely different from that perceived in the unbiased state. For example, if an observer's natural bias was to perceive the ambiguous stereoscopic surfaces (defined by the disparities of 10,000 points) as uncrossed/behind, a sufficient number of unambiguous bias points with crossed disparity (560 on average) could pull the entire surface to the front. There was no significant difference between the younger and older observers in the numbers of bias points that were required to obtain stereoscopic “pulling”.