Abstract
In the typical Julesz display, subjects view random-dot stereograms in which dots in each depth plane are adjacent. However, Tsirlin, Allison, & Wilcox (JOV/8/5/5) intermingled dots with different disparities to create transparent, overlaid, depth planes. With free viewing and unlimited time to search and re-fixate, their subjects could distinguish up to six such depth planes. We now report that naïve subjects achieve this by scanning the display, noting only two or three planes at a time. However, after many hours of practice, experienced subjects can, in optimal conditions, accurately distinguish six to eight depth planes in a random display within 400 ms. (We provide unlimited exposure to just the first and last planes, to facilitate fusion, before completing the display for the specified time.) The new result supports theories of stereopsis in which the simultaneous analysis of multiple depth planes is possible, even without spatial adjacency.