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Jose Medina, Tim Meese, Kathy Mullen; Cross-orientation masking in the red-green isoluminant and luminance systems. Journal of Vision 2007;7(9):257. doi: https://doi.org/10.1167/7.9.257.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Cross-orientation masking (XOM) is defined psychophysically as the phenomenon whereby detection of a test grating is masked by the presence of a superimposed stimulus at an orthogonal orientation. A previous study found that XOM for achromatic stimuli is strongest at mid-high temporal and low spatial frequencies, the putative M cell range (Meese and Holmes, Proc. R. Soc. B., 274, p127, 2007). Here we investigate whether color vision can support XOM by using red-green isoluminant stimuli, and achromatic stimuli for comparison with the luminance system.
Methods: Horizontal Gabor stimuli (Gaussian contrast envelope, σ=2 degrees) were modulated at two spatial (0.375 & 0.75cpd) and two temporal frequencies (2 & 4Hz). An orthogonal vertical Gabor patch with the same spatio-temporal configuration was superimposed (i.e. a plaid). Binocular contrast detection thresholds were determined using a temporal 2AFC staircase method over a wide range of mask contrasts (scaled in multiples of detection threshold).
Results: We find three new results for color vision: 1. robust XOM for color vision for the spatio-temporal frequencies tested over a wide range of mask contrasts; 2. greater cross-orientation facilitation at low mask contrasts for chromatic than for achromatic stimuli, and 3. significantly greater masking for the chromatic than the achromatic stimuli when mask contrast is high.
Conclusions: Such robust and distinct chromatic masking effects indicate that M cells do not exclusively support cross orientation masking in this spatio-temporal range and suggest differential constraints on chromatic compared to achromatic cross-orientation suppression along the cortical or subcortical streams.
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