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What determines the reference framework for stereopsis? Andrew Glennerster, Martin Birch and Suzanne McKee* University Laboratory of Physiology, Oxford *Smith-Kettlewell Eye Research Institute, San Francisco
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Viewing geometry
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Depth in fronto-parallel coordinates L R Fixation plane
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Depth relative to a local surface L R Mitchison and McKee (85, 87) Mitchison and Westheimer (84) Reference plane
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Depth perpendicular to a local surface L R
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Prediction L R Threshold planes, according to ‘surface’ hypothesis Thresholds should all be the same, according to ‘fronto-parallel’ hypothesis
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Prediction L R Threshold planes
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Interleaved psychometric functions L R Threshold planes
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Stimulus details Target column 4 Task is central column in front or behind the plane of the grid? dot size 2 arcmin pixel size 0.45 arcmin anti-aliased viewing distance 2.65 m exposure 600 ms grid disparity gradient +/- 0.1 slant about a vertical axis modified Wheatstone stereoscope Stimulus Psychometric procedure method of constant stimuli 7 disparities per psychometric function (at least 1400 trials) 3 psychometric functions interleaved …
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Results: grid disparity gradient -0.1 Subject MDB
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Grid disparity gradient +0.1 Subject MDB
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Grid disparity gradient -0.1 Subject AG
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Grid disparity gradient +0.1 Subject AG
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Summary of thresholds RcycLR L Threshold (arcmin) MDB 12% difference p < 0.001 (one-tailed t-test) 23% diff. p < 0.0001
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Summary of thresholds RcycLR L Threshold (arcmin) AG 15% difference p < 0.01 12% diff. p < 0.01
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Summary Threshold planes Thresholds for detecting relative disparity depend on the local surface slant Thresholds are lowest when the displacement is more orthogonal to the surface
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Conclusion The visual system may represent depth in a surface-based coordinate frame... … and hence be much less sensitive to rotations and translations of the head
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Conclusion The visual system may represent depth in a surface-based coordinate frame... … and hence be much less sensitive to rotations and translations of the head
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Comparison with lateral displacement thresholds Key: F-P grid, lateral judgement Width of grid in the eye in which the target was displaced (arcmin) Target column Slanted grid (+0.1) depth judgement Slanted grid (-0.1) depth judgement Subject MDB
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Sensitivity to lateral displacement Subject MDB
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… and to disparity + lateral displacement Subject MDB
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… and to disparity + lateral displacement Subject MDB
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Grid gradient 0.1 Subject MDBSubject SPM
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Grid gradient +0.1 and -0.1 Subject MDB
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Local surface model Subject MDB +0.1 gradient-0.1 gradient
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Interleaved slants Subject MDB +0.4 arcmin disparity-0.4 arcmin disparity
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Effect of perceived slant Subject MDB Grid perceived as fronto-parallel: Grid perceived as slanted:
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