Determinants of fusion of dichoptically presented orthogonal gratings

Liu, Tyler, and Schor (1992 Vision Research 32 1471-1479) reported the surp rising finding that dichoptically presented orthogonal sine-wave gratings d o not always produce binocular rivalry. Gratings of high spatial frequency, and especially of low contrast, fuse to produce a stable percept of a dich optic plaid. Using a somewhat different perceptual task, we replicated thos e findings and extended them. The probability of a plaid percept is higher for square-wave gratings than for sine-wave gratings, and higher still for rectangular-wave gratings with high duty cycles (with very thin light or da rk bars). Experiments were conducted to test whether this duty-cycle effect was due to changes in overall luminance, or in the size of the regions of luminance congruity (which may reduce the probability of rivalry), but no s uch effects could account for the results. The presence of locally conflict ing contour information in the two eyes was shown to be an important determ inant of rivalry onset, but, since removing such regions did not eliminate rivalry, other factors also have a role to play. The spatial frequency comp osition of the gratings is one such factor which is consistent with all of the findings we report.