Interpolation in stereoscopic matching.

Anyone who has stared at a repeating wallpaper pattern, or a periodic pattern of tiles, has probably experienced the phenomenon of a false stereoscopic depth percept. This arises because of a mismatching in the two eyes of repeating elements in the pattern. The phenomenon is less likely to occur if an edge of the textured region is in view; the edge seems to fix the registration of elements. We describe here a stereogram which exemplifies this principle; it has a central, periodic region bounded on either side by edges with pre-assigned disparities. We find that the perceived depth of the central region is controlled by the edges. In certain conditions (when the period is spatially large), the edges simply impose one of the expected discrete matchings. In other conditions, however, we observe a striking phenomenon: interpolation in depth occurs between the edges, violating any possible feature-by-feature matching.