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Saumil S. Patel, Harold E. Bedell; Non-horizontal disparities enhance sensitivity of the human stereovision system. Journal of Vision 2005;5(8):261. doi: 10.1167/5.8.261.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose>> Several studies have shown that disparity information provided by the non-vertical spatial frequency (SF) components in a stimulus exert a substantial influence on the perception of stereoscopic depth. Here, we tested how non-horizontal disparity information contributes to the sensitivity of the human stereovision system by comparing stereothresholds for orientationally broad- and narrow-band stimuli with equal contrast in their vertical SF components. Methods>> Stereothresholds were measured in 2 subjects for SF band-pass (2–4 cpd) and orientation low-pass filtered random-dot stimuli (mean luminance = 3 cd/sq. m), using the method of constant-stimuli. Broad-band stimuli included SF components at all orientations from vertical (0 odeg) to the cut-off orientation of 89 odeg. Narrow-band stimuli with a cut-off orientation of 15 odeg were tested for comparison. All SF components that did not belong to the selected spatio-orientation band were removed. To maintain orientation balance, a corresponding band of negative orientations was present in each stimulus. The RMS contrast was 0.21 cd/sq. m for broad-band stimuli and 0.15 cd/sq. for narrow-band comparison stimuli. These values produce equal contrast of the broad-band and narrow-band stimuli within the 15 odeg orientation band. Results>> Stereothresholds for the broad-band stimuli are lower by a factor of approximately 2.5, compared to those obtained with the near-vertical narrow-band stimuli. Similar results were obtained when the RMS contrast of the broad-band stimuli was 0.31 cd/sq. m. Conclusions>> The results provide clear evidence that optimal stereo-sensitivity depends on disparities in SF components outside the ±15 odeg band. We conclude that disparity signals from vertically and non-vertically tuned neural mechanisms are pooled prior to computation of horizontal image disparity and that this pooling substantially enhances the signal to noise ratio of the stereovision system.
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