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Erik Börjesson, Leo Poom; Visual slant-contrast across space and attributes. Journal of Vision 2002;2(7):91. doi: 10.1167/2.7.91.
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Purpose: The perceived slant of a test figure depends on the cue specifying the slant of an inducer (van Ee, Banks, & Backus, 1999). Slant repulsion occurs when relative disparity signals the inducer slant. Attraction occurs when monocular cues are used. We investigated the slant effects with regard to depth separation and lateral separation between inducer and test figure. Methods: Stereoimages were created showing a circular inducer (7.5 deg diam). The slant of the inducer was defined either by perspective, shading, motion or disparity. A central vertical test figure could be rotated in stereoscopic depth by the observer. The task was to adjust the test figure to the apparent vertical. Inducer slant varied between −60 to 60 deg. The lateral separation between the inducer and the test figure was varied in the first experiment. The stereoscopic depth separation between the inducer and test figure was varied in the second experiment. Finally, the possible effect of a frontoparallel reference frame was investigated. Results: 1) The repulsion and attraction effects (van Ee et al, 1999) were reproduced. 2) There were no pronounced effects of spatial separation up to 7 deg for either attraction or repulsion. 3) With depth separation the attraction was still present whereas the repulsion was reduced. 4) Both attraction and repulsion decreased when a frame surrounded the inducer. Conclusion: Both attraction and repulsion are spatially long-range processes, but contrary to the attraction the slant repulsion effect does not generalize in stereoscopic depth. The effects of a reference frame surrounding the inducer further demonstrate the spatial long-range modulation of perceived slant. It's hypothesized that slant from disparity is estimated by depth specific processes, contrary to slant from monocular cues. Finally, no slant attraction has been found after adaptation to monocular cues suggesting different processes for slant adaptation and simultaneous slant effects (Poom & Börjesson, 1999).
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