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Laurie M Wilcox, Rick Wildes, Deepak Lakra; Depth ordering in natural stereoscopic images: The role of monocular occlusion. Journal of Vision 2003;3(9):852. doi: 10.1167/3.9.852.
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© ARVO (1962-2015); The Authors (2016-present)
Rationale. There is convincing evidence that monocular occlusion regions aid stereoscopic vision (Gillam & Borsting, 1988) and that this enhancement requires ecological arrangement of the stimuli (Nakayama & Shimojo, 1990; Grove & Gillam, 2001). Existing studies have, for good reason, used simple stimuli. Here we ask if the advantage provided by monocular occlusion information is generalizable to more complex images containing multiple cues to depth. Methods. Images of highly textured boxes were taken with a stereoscopic camera arrangement at three distances. The stimuli were positioned in front of a textured planar background, which was orthogonal to the parallel optical axes of the cameras. The images were digitally manipulated to create stereopairs in which occlusion regions were present or absent. All imges were randomly presented as depth-correct or, by reversing the left and right eye images, as depth-reversed. A high-resolution 3D projector, with back projection and Stereographics shutter glasses were used to present the stimuli stereoscopically. The observers' (n=12) task was to indicate as quickly and accurately as possible whether the depth ordering was correct or reversed. Results. In spite of the presence of multiple cues to depth (overlap, shading, texture and stereopsis) the presence of the monocular occlusion regions reduced the amount of time needed to discriminate the depth relationships in the scene. On the ‘depth-correct’ trials this advantage improved as the size of the occluded region increased; as expected, there was no such improvement in the ‘depth-reversed’ conditions. Conclusions. Monocular occlusion information has a substantial effect on the perception of depth in natural images. The fact that this advantage persists in the presence of multiple depth cues suggests that such monocular regions play an important role in the interpretation of depth ordering at object boundaries.
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