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Emily A. Cooper, Johannes Burge, Martin S. Banks; The vertical horopter is not adaptable, but it may be adaptive. Journal of Vision 2011;11(3):20. doi: https://doi.org/10.1167/11.3.20.
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© ARVO (1962-2015); The Authors (2016-present)
Depth estimates from disparity are most precise when the visual input stimulates corresponding retinal points or points close to them. Corresponding points have uncrossed disparities in the upper visual field and crossed disparities in the lower visual field. Due to these disparities, the vertical part of the horopter—the positions in space that stimulate corresponding points—is pitched top-back. Many have suggested that this pitch is advantageous for discriminating depth in the natural environment, particularly relative to the ground. We asked whether the vertical horopter is adaptive (suited for perception of the ground) and adaptable (changeable by experience). Experiment 1 measured the disparities between corresponding points in 28 observers. We confirmed that the horopter is pitched. However, it is also typically convex making it ill-suited for depth perception relative to the ground. Experiment 2 tracked locations of corresponding points while observers wore lenses for 7 days that distorted binocular disparities. We observed no change in the horopter, suggesting that it is not adaptable. We also showed that the horopter is not adaptive for long viewing distances because at such distances uncrossed disparities between corresponding points cannot be stimulated. The vertical horopter seems to be adaptive for perceiving convex, slanted surfaces at short distances.
θ v is the angle between the vertical meridians. θ h is the angle between the horizontal meridians (cyclovergence). θ r is the difference between the two, indicating the amount of retinal shear between corresponding points. All of these studies used apparent-motion except: abinocular apparent vertical and horizontal; bmonocular apparent vertical. For Siderov et al. (1999): 1viewing distance = 200 cm; 2viewing distance = 50 cm.
*Values obtained from Ogle (1950). When values were given for various fixation distances, the farthest distance was used.
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