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Yeon Jin Kim; Distinct mechanisms for monocular and dichoptic cross-orientation masking revealed by their time courses. Journal of Vision 2014;14(15):70. doi: 10.1167/14.15.70.
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We compared the time courses of monocular and dichoptic contrast normalization using a cross-orientation masking (XOM) paradigm and found clear evidence for distinct mechanisms for each. Methods: We measured detection thresholds for horizontal Gabor test stimuli overlaid with vertical Gabor masks (fixed at ×10 detection threshold) as a function of the duration of the stimuli (TvD) for monocular and dichoptic presentations at two spatial frequencies (0.375 and 1cpd). We used three contrast types: color-only (red-green color test and mask), luminance-only (luminance test and mask) and a cross-condition (color test and luminance mask). We compared the timing for monocular and dichoptic XOM for all conditions by determining the slope for each TvD data set. This allowed us to determine the time course of monocular and dichoptic masking in luminance vision, color vision and their combination. Results: We found marked differences between the monocular and dichoptic conditions: the slopes for monocular masking are significantly steeper than that for dichopitic masking, showing a decline in masking with time. There were no differences between contrast types or spatial frequencies. Particularly, monocular masking was strongest at short durations and decreased to approach a plateau for all conditions. For the color-luminance condition, strong facilitation was observed. In comparison, dichotic masking was largely constant across stimulus duration for all conditions. Conclusion: Monocular and dichoptic masking involve two distinct mechanisms: monocular masking is stimulus-duration dependent and transient, while dichoptic masking is stimulus-duration independent and sustained.
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