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Brian Rogers, Charlotte Colam, Christopher Cant; Sensitivity to disparity modulations in ground plane surfaces. Journal of Vision 2008;8(6):1087. doi: 10.1167/8.6.1087.
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© ARVO (1962-2015); The Authors (2016-present)
Tyler (1974, Nature, 251, 140–2) and Rogers and Graham (1982, Vision Research, 22, 216–70) have shown that sensitivity to horizontally oriented disparity corrugations is maximal at a corrugation frequency of between 0.3 and 0.5 cycles/deg and falls off at both lower and higher frequencies. A similar band-pass characteristic has also been observed for vertically oriented corrugations except that sensitivity is poorer at low corrugation frequencies for most observers — the stereoscopic anisotropy. In contrast, almost nothing is known about the visual system's sensitivity to disparity modulations of ground plane surfaces. In the present study, disparity thresholds were measured using a 2AFC procedure for sinusoidal depth corrugations of the ground plane (furrows) lying either along (near-to-far) or across (left-to-right) the observer's line-of-sight. Ground plane stereoscopic images were produced by projecting two large (2 m × 1.5m) random texture patterns onto two floor-mounted screens on either side of the observer. The images were viewed via a mirror stereoscope so that the corrugated surface appeared to extend into the distance in front of the observer. The number of corrugations across the surface was varied between 2 and 32, corresponding to corrugation frequencies of between ∼0.1 and 2.0 cycles/deg in the central region of the display. Lowest thresholds were found to be between 5 and 10 arc sec (peak-to-trough) for corrugations oriented across the line-of-sight, at an optimum corrugation frequency of ∼0.5 cycles/deg. Thresholds were slightly higher (×1.5) for corrugations oriented in a near-far direction, providing evidence for an analogous anisotropy in the perception of ground plane surfaces. Thresholds were also determined for discriminating (i) the slant of planar surfaces away from the horizontal and (ii) the direction of curvature (convex vs concave) of surfaces close to the ground plane. Slant and curvature thresholds were also found to be in the hyperacuity range - corresponding to an ability to detect (i) planar surfaces with 2–4 deg of slant away from the horizontal and (ii) curved surfaces with a radius of curvature [[gt]] 15 m.
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