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Mina Gheiratmand, Kathy T. Mullen; Cortical color-luminance contrast interactions revealed by dichoptic masking. Journal of Vision 2010;10(15):55. doi: https://doi.org/10.1167/10.15.55.
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A range of psychophysical experiments have revealed the existence of separate luminance and color mechanisms in the human visual system. Analysis of the visual scene, however, requires the integration of color and luminance contrasts. We used suprathreshold masking to investigate interactions between color and luminance mechanisms with a focus on the orientation tuning properties. To assess interactions specific to the cortical stage of processing, dichoptic and monoptic presentations were compared.
Methods: Test stimuli were red-green isoluminant horizontal Gabors (0.75cpd, 2Hz) and masks were chromatic or luminance Gabors of the same spatial and temporal frequency as the test. Test detection was measured as a function of mask contrast with a vertical overlay mask (cross orientation masking), or as a function of mask orientation with a high contrast mask (orientation tuning).
Results: With a red-green test and mask we found that dichoptic masking was stronger than monoptic and was orientationally tuned, while no tuning was found for monoptic presentations, supporting our previous results (Gheiratmand, et al., J Vis 9(14): 84, 2009). With a red-green test and luminance mask, very significant differences between dichoptic and monoptic presentations were found. Dichoptic presentations showed strong masking effects, whereas monoptic presetations showed facilitation. These color-luminance interactions showed no orientation tuning.
Conclusion: There are non-oriented interactions between color and luminance mechanisms at high contrasts, however, these only occur in dichoptic presentations indicating a cortical origin. The differences between dichoptic and monoptic masking in color-luminance and color-color interactions suggest that distinct neural mechanisms are involved in monoptic and dichoptic conditions.
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