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Haluk Ogmen, Bruno G. Breitmeyer, Hulusi Kafaligonul, Steven Todd, Lynn Mardon, Ralph Ziegler; Temporal aspects of contour and brightness processing in meta- and paracontrast. Journal of Vision 2006;6(6):122. doi: 10.1167/6.6.122.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose. Existing evidence suggests that stimulus contours are processed faster than surface brightness or color. We investigate the temporal dynamics of contour and brightness visibility during meta- and paracontrast and use an updated RECOD model of visual masking to account for the findings.
Methods. Stimuli were a 0.85 deg disk (T), surrounded by a ring (M), 0.42 deg wide and separated by 0.05 deg, centered 1.4 deg above and 1.6 deg to the right of fixation. In the brightness masking, a match stimulus the same size as T was presented symmetrically to the left of fixation. In the contour masking, T was either a complete disk or one with either a lower or upper contour deletion.
Results. Whereas optimal metacontrast SOA was 10–15 ms in contour masking, it was 40 ms in brightness masking. In paracontrast 1) a local minimum of visibility was obtained around an SOA of −170 ms for both tasks, 2) a local enhancement of brightness visibility was obtained at an SOA of −40 ms, and c) a second period of suppression was evident, particularly in contour masking, at an SOA of −10 ms.
Conclusion. Brightness and contour are processed by separate slow and fast cortical parvo pathways, each subject to intrachannel inhibition and to interchannel inhibition by the still faster cortical magno activity. In addition, subcortical modulatory processes activated by the paracontrast mask may enhance the parvo brightness activity to the following target. These conclusions are supported by simulations of an updated RECOD model.
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