Required 8 female Os (mean age = 22.7 yr.) to report stereoscopic size and distance of the enclosed lines of a Ponzo configuration as a function of their magnitude and direction of disparity. The magnitude of the illusion varied directly with the apparent size of the disparate lines, and the illusion persisted even when the critical contours appeared in different stereoscopic depth planes. (19 ref.) (PsycINFO Database Record (c) 2006 APA, all rights reserved)