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David Alais, John Cass, Branka Spehar, Colin Clifford; Temporal masking within and between chromatic and achromatic axes. Journal of Vision 2007;7(9):378. doi: 10.1167/7.9.378.
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© ARVO (1962-2015); The Authors (2016-present)
Previous temporal masking studies using iso-oriented, luminance-defined (LD) target and masking stimuli have estimated that there exist two sets of temporal channels: one low pass and one or two higher bandpass channels (Anderson & Burr, 1985; Hess & Snowden, 1992). Recent data indicate that low-pass masking only occurs between iso-oriented stimuli, while the higher bandpass masking is iso-tropic (Cass & Alais, 2006). To investigate whether this implies a functional distinction between precortical and cortical levels of temporal processing, we conducted analogous temporal masking experiments with iso-oriented chromatic gratings (1 cpd). We did this both within LD and chromatic axes (L−M & S−(L+M)), as well as between these axes. Although chromatically-defined modulation transfer functions are distinctly low-pass, we found temporal masking functions within-chromatic channels that were qualitatively similar to those found with achromatic stimuli: one lowpass channel and a higher bandpass channel. This result challenges current models, which assume that chromatic channels are entirely low-pass, and resolves an apparent contradiction between these models and data from speed discrimination experiments with chromatically-defined stimuli (Cropper, 1994; Metha & Mullen, 2000). Interestingly, conditions testing masking between chromatic axes (S−(L+M) vs. L−M) also revealed both lowpass and higher bandpass channels, suggesting that in the context of chromatic stimuli, both temporal channels are probably cortically mediated. We also confirmed previously reported asymmetries whereby L−M stimuli robustly masked LD targets, but not vice versa.
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