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Kathy T. Mullen, Mina Gheiratmand, José M. Medina, Yeon Jin Kim; Two routes to suppression of signals in color vision. Journal of Vision 2012;12(9):107. doi: 10.1167/12.9.107.
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There are at least two routes to psychophysical cross-orientation suppression prior to binocular summation of the signal in achromatic vision: (1) a monoptic, non-adaptable sub-cortical pathway and (2) a dichoptic, adaptable interocular pathway (Baker et al., Neuroscience, 146, 2007). Here we test psychophysically whether cross orientation masking (XOM) in color vision (Medina & Mullen, JOV 9(3), 2009) has gain-control pathways that are separable from achromatic responses or whether chromatic and achromatic responses interact. Methods: Detection threshold vs contrast (TvC) masking functions were measured for red-green isoluminant, horizontal Gabor targets overlaid with achromatic vertical Gabor masks. We tested for XOM under a range of spatiotemporal conditions (0.375, 0.75 & 1.5 cpd; 2 & 8 Hz), and with the chromatic test and achromatic mask presented under monoptic, dichoptic, and binocular viewing conditions. Results: We find that: (1) there is little or no cross orientation masking of color by achromatic contrast under monoptic or binocular conditions at any of the spatio-temporal frequencies tested, although some facilitation may occur; (2) there is significant dichoptic XOM, when mask and test are present to different eyes, which increases with mask contrast; (3) the dichoptic XOM is greater at low temporal frequencies (2 Hz) than high (8Hz). Conclusion: The significant inter-ocular cross orientation suppression of color by luminance contrast indicates that gain control pools at this level are unselective for chromaticity. Our results support a two-stage contrast normalization model with both a monocular and a dichoptic stage prior to binocular summation: the within eye, monocular stage of suppression is selective for color contrast whereas the inter-ocular second stage, revealed under dichoptic conditions, has color-achromatic interactions. This differential effect provides evidence for at least two distinct sites for suppressive gain control in color vision.
Meeting abstract presented at VSS 2012
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