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Martin Banks, Bjorn Vlaskamp, James Hillis, Jonathan Gardner; Stereopsis at isoluminance. Journal of Vision 2007;7(9):806. doi: 10.1167/7.9.806.
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© ARVO (1962-2015); The Authors (2016-present)
In early visual processing, cone outputs are converted into achromatic and chromatic channels with different spatial and temporal properties. Some investigators have reported that stereopsis is deficient with isoluminant stimuli (Lu & Fender, 1972; De Weert, 1979), suggesting that chromatic channels do not support depth from disparity. Others found that stereopsis with chromatic stimuli is not deficient once the effective contrasts of isoluminant and achromatic stimuli are taken into account (Scharff & Geisler, 1992; Krauskopf & Forte, 2002). These disparate psychophysical observations might be reconciled by considering the binocular properties of cortical neurons. The ocular-dominance histograms of chromatically selective neurons do not differ significantly from the histograms of chromatically non-selective neurons (Peirce et al., 2003). However, chromatically selective neurons have low-pass spatial-frequency tuning. Thus such cortical mechanisms might support stereopsis, but only for half images with power at low spatial frequencies and for depth corrugations that are low in spatial frequency. To test this hypothesis, we measured disparity thresholds with isoluminant and luminance-varying stimuli while varying spatial-frequency content. The stimuli were random-dot stereograms with sinusoidal depth corrugations. The half images were gray backgrounds textured with Gaussian blobs that differed in luminance and/or hue. To determine if spatial frequency is an important determinant of stereopsis at isoluminance, we varied the frequency content of the half images and the spatial frequency of the corrugations. We also measured the perceptual salience of the half images for all experimental conditions. At high spatial frequency, we observed significant deficits with isoluminant stimuli compared to equally salient, luminance-varying stimuli. At low frequency, we observed no such deficit. Thus, the relative deficiency of stereopsis at isoluminance depends strongly on the spatial-frequency content of the stimuli. These psychophysical observations are therefore consistent with our understanding of the processing of binocular information in visual cortex.
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