Depth in anticorrelated random dot stereograms (RDS)

Abstract

Global depth seen in densely seeded RDS is not perceived in anticorrelated RDS (opposite sign of brightness contrast on corresponding loci) whether the dots are at rest or in motion, as extant data show. We report that global, disparity-dependent depth appears in anticorrelated RDS that are flashed repetitively with an interocular delay. During the delay, a dot array in one eye was paired with a gray frame in the other eye and presumably could interact with the negative afterimage of the contralateral dot array. In anticorrelated RDS with 8 arcmin dots at 10% to 50% density and a 15-ms flash, robust depth was produced by interocular delay on the order of 45-75 ms. In correlated (otherwise identical) RDS, depth deteriorated sharply with delays larger than 45 ms. The range of delays producing depth was dependent on flash duration, dot size, and dot density. Surprisingly, anticorrelated RDS displayed continuously showed disparity-dependent depth at low (1 %) dot density provided the dots were larger than some 2 arcmin; as dot density was increased depth became harder to see, but depth became visible when such RDS were flashed with an interocular delay. Our results suggest that all stereoscopic depth signals emerge exclusively from same-sign binocular cortical filters.