Abstract

We have investigated the parameters under which a new stereo illusion may be observed. If a single grating is viewed with both eyes, the grating appears to have several levels of depth. The levels of depth are simultaneously visible but are discontinuous with sharp borders at their boundaries. Photographic prints of square-wave gratings were viewed binocularly. The prints had a mean luminance of 150 cd/m² and a contrast of 75%. The subject's task was to state the number of levels of depth seen. One (1) indicating a single surface, regardless of its appearance, was reported even if the surface appeared wavy, individual bars tilted in depth, or one level could be seen through a transparent second level without discontinuities. The sensation of several levels of depth disappeared if one (1) closed one eye and viewed the pattern monocularly, (2) oriented the pattern horizontally, or (3) increased or decreased the spatial frequency from an optimum of 3–4 cpd. Although the illusion is observed when a single grating is viewed binocularly, it can be accounted for, in part, by the same mechanisms which cause the illusion of a plane tilted in depth when two gratings of differing spatial frequencies are presented dichoptically.

© 1985 Optical Society of America