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Srinivasa Varadharajan, John M. Foley; Effect of flanking patterns on contrast discrimination at different eccentricities. Journal of Vision 2002;2(10):102. doi: https://doi.org/10.1167/2.10.102.
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TvC functions for contrast discrimination of a Gabor Pattern (sf = 4 c/deg, sd = 0.25 deg, dur = 90 msec) were measured at horizontal eccentricities of 0 and 4 deg using 2 AFC and Quest. The measurement was made with and without the simultaneous presentation of two flanking Gabor patterns (sf = 4 c/deg, sd = .25 deg) of fixed contrast (−6 and −16 dB re 1), aligned or orthogonal to the test pattern, and offset by 3 or 4 wavelengths with no overlap. At 0 deg, without the flankers, the TvC function has a dipper shape. With the flankers, the absolute threshold is similar or lower; the TvC function starts to rise at a higher pedestal contrast and meets the no flanker TvC at high contrast. At 4 deg, without the flankers, the TvC function has a scallop or second minimum at high pedestal contrast. With the flankers, the absolute threshold is similar or higher and the TvC function starts to rise at lower pedestal contrast. It also has a scallop or second minimum at high pedestal contrast, may cross the no flanker TvC function, and meets it at high contrast. Aligned and orthogonal flankers had similar effects over most of the pedestal contrast range, but, in general, there was more facilitation with the orthogonal flanker. Some TvC functions deviate from these forms. These phenomena can be described by a model with a few nonlinear pattern mechanisms that interact via divisive inhibition (Foley, 1994) and multiplicative sensitivity modulation (Chen & Tyler, 2001). The second minimum is attributed to a second mechanism sensitive to the test pattern, but less sensitive than the first.
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