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Mina Gheiratmand, Tim S. Meese, Kathy T. Mullen; Cross orientation masking in color vision: Cortical processing assessed with dichoptic presentation. Journal of Vision 2009;9(14):84. doi: 10.1167/9.14.84.
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“Introduction: Detection of a Gabor pattern may be impaired in the presence of a similar pattern of orthogonal orientation, a phenomenon known as cross-orientation masking (XOM). We have previously reported that cross orientation masking (XOM) for red-green (RG) isoluminant stimuli is greater than achromatic XOM and isotropic, supporting the involvement of P cells or their cortical projections in this nonlinearity (Medina & Mullen, JOV 9(3):20,1, 2009). It is unclear, however, whether this chromatic masking originates at a cortical or subcortical level, although a cortical level is implicated as the responses of subcortical P cells are essentially linear. Here we use dichoptic presentations to investigate the cortical involvement of chromatic XOM.
Methods: Test and mask stimuli were overlaid orthogonal Gabor patterns with the same spatio-temporal conditions and with test and mask presented dichoptically to different eyes. Spatial frequencies were 0.375 or 0.75cpd, counter-phased at 2 or 4 Hz. Stimuli were RG isoluminant or achromatic control stimuli. We obtained threshold vs. contrast masking functions using a staircase method to measure detection thresholds.
Results: We find that there is dichoptic masking in color vision, similar to that found for achromatic vision. The dichoptic masking is stronger than the monoptic masking in color vision, an effect that has also been found in achromatic vision (Meese & Baker, JOV 9(5):2,115, 2009). In general, however, monoptic masking and dichoptic masking show less difference in magnitude in color vision than in achromatic vision. We also find that dichoptic masking is orientationally tuned whereas monoptic masking in color vision has isotropic properties.
Conclusions: Our results are superficially compatible with a greater involvement of a cortical sites in color compared to achromatic XOM. The difference in properties, such as orientation tuning, between monoptic and dichoptic masking suggest that there may be more fundamental differences between monoptic and dichoptic masking conditions”
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