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Michael Landy, Zachary Westrick; Texture mechanisms pool multiple first-order channels. Journal of Vision 2013;13(9):628. doi: 10.1167/13.9.628.
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© ARVO (1962-2015); The Authors (2016-present)
The filter-rectify-filter (FRF) model is a popular model of texture segregation. In FRF, images are (1) processed by linear filters to isolate a constituent texture, (2) rectified yielding a texture-intensity image, and (3) filtered again to detect the texture-defined signal. In FRF there is an interaction between first-stage filter bandwidth and second-order contrast sensitivity: If the first-stage filter is tuned for the texture carrier with typical bandwidth for V1, predicted sensitivity to high-frequency texture modulation is much lower than measured human sensitivity. Human performance is consistent with an FRF model with much higher first-order bandwidth. We report two tests of the following hypothesis: Second-order mechanisms achieve broad first-order bandwidth by pooling over multiple first-order channels to preserve high-frequency second-order sensitivity. Methods: Expt. 1: Cross-carrier adaptation. Observers adapted to a second-order grating. We measured detection threshold (2IFC) for a second-order grating with identical second-order spatial-frequency, but possibly differing in orientation and/or carrier frequency from the adapter. We estimated the degree of orientation-specific, cross-carrier adaptation as the ratio of detection thresholds for same vs. different second-order orientation (relative to adapter orientation). Expt. 2: Dependence of threshold on carrier contrast: We measured threshold for orientation discrimination (vertical vs. horizontal second-order grating, 2AFC) as a function of second-order spatial frequency and first-order carrier contrast. Results and Conclusions: Expt. 1: We found cross-carrier adaptation even when carriers differed by a factor of four, indicating that second-order mechanisms are sensitive to a broad range of carrier frequencies. Expt. 2: Relative sensitivity to high-frequency gratings dropped dramatically with reduced first-order contrast. This is because detection of a high frequency modulator depends on first-order responses to frequencies distant from the carrier that drop below threshold at low contrasts. Both results are consistent with second-order mechanisms that receive input from first-stage filters with diverse tuning properties.
Meeting abstract presented at VSS 2013
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