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Barbara Gillam, Harold Sedgwick, Phillip Marlow; Local and non-local effects on surface-mediated stereoscopic depth. Journal of Vision 2010;10(7):325. doi: 10.1167/10.7.325.
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© ARVO (1962-2015); The Authors (2016-present)
The magnitude and precision of stereoscopic depth between two probes can be mediated by the disparity of each relative to a common background surface (e.g. Glennerster & McKee, VR 1999). For example, the common underestimation of background surface slant produces a bias in relative probe depth. Gillam & Sedgwick (ARVO 2000) have shown that this bias is reduced when flanking surfaces in the frontal plane reduce underestimation of background surface slant. Here we manipulate the relations between flanking surfaces, background surface, and probes to explore the propagation of slant across surfaces and from surfaces to isolated objects. In our first experiment observers set two disc probes to apparent equidistance when viewed naturally against a horizontally slanted rectangular random dot surface whose height was varied. Frontal plane random dot rectangles abutted this surface above and below. The bias in the probes increased as surface height/flanker distance increased but even with flankers 4.4 deg from the probes, bias was less when flankers were present. In a second similar experiment the flankers were slanted and a central background surface, when present, was in the frontal plane. For flankers alone probe bias did not diminish up to a 4.4 deg.separation of flankers and probes. The addition of a central frontal plane background surface strongly reduced this bias as the separation of the flankers increased regardless of whether the central surface filled the gap between flankers or was of constant height in the centre. These results may be related to changes in contrast effects from flankers to background. Stereoscopic depth between probes is thus influenced by a common background surface, by neighboring surfaces acting (contiguously or non-contiguously) on the background surface, and by distant surfaces acting directly on the probes. These local and non-local effects are determined by the overall configuration of probes and surfaces.
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