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Lynn A. Olzak, Jordan R. Wagge, Robin D. Thomas; Mid-level pattern masking: Contrast or response gain control?. Journal of Vision 2011;11(15):56. doi: 10.1167/11.15.56.
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Masking in fine orientation or spatial frequency discriminations can be observed when masks of very different spatial frequency or orientation, respectively, are overlaid on a target sinusoid. Masking (or slight facilitation) can also occur when masks of similar spatial frequency and orientation are presented in as annulus surrounding the target patch. We evaluated the relative contributions of contrast and response gain in accounting for the contrast response functions in these tasks, which shift curves horizontally (contrast gain) and/or vertically (response gain). The target was always a 15 cpd grating, upon which spatial frequency or orientation discriminations were made. In different sessions, masks were either overlaid or positioned as an annulus, and were presented either at 2% or 25% contrast. Within each session, target contrast was randomly varied equal linear steps from 3.1% contrast to 25% contrast (3.1%, 6.3%, 9.4%, 12.5%, 15.6%, 18.8%, 21.9%, and 25%) to generate contrast response functions. We fit Naka-Rushton functions to the data, with parameters C50 and Rmax free to vary. The functions accounted for the data well. There was no contribution of contrast gain in the 2% mask conditions, but at the higher mask contrast, combined contributions from both types of gain were required.
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