The Role of Monocularly Conspicuous Features in Facilitating Stereopsis from Random-Dot Stereograms

Two experiments are reported which investigated the effects on stereopsis perception times of including monocularly conspicuous features in random-dot stereograms. It was found that such features facilitated stereopsis in large-disparity but not in small-disparity stereograms, perception times for the latter being relatively short with or without monocular features. Facilitation in the large-disparity stimuli came about both from features which delineated the shape of the whole disparate area and from features which merely happened to lie in the same depth plane as the disparate area, but which did not give any shape cues. It is argued that these various results can be well accounted for by a ‘vergence hypothesis’, which supposes that the long perception times often found with random-dot stereograms are due in part to the absence of stimulus features which can guide the vergence movements necessary for fusing the display.