DEPTH FROM BINOCULAR-RIVALRY WITHOUT SPATIAL DISPARITY

Some new stereoscopic effects are reported that arise from dichoptic s timuli containing no binocular disparity. In one effect, identical arr ays of small black discs are presented to the two eyes and slightly sm aller white discs are superimposed on one of each pair of black discs. This creates the impression of a surface with holes in it, through wh ich is seen a surface with fluctuating black and white areas. This is referred to as the 'sieve effect'. The white discs must subtend less t han about 1 deg of visual angle. With larger discs the black and white areas no longer exhibit alternating rivalry but combine to produce bi nocular lustre. This destroys the sieve effect. The sieve effect is we ak or nonexistent when the black and white discs are the same size, sh owing that well-defined binocular rims are required for the effect. Wh en the monocular white discs are reduced to dots, the impression of a surface seen through holes gives way to the impression of an array of dots behind or standing out from the background. In this case the mono cular dots permanently dominate the homogeneous backgrounds in the oth er eye and the impression of depth can be explained in terms of appare nt parallax or of disparity due to the instability of vergence.