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Norma Graham, S. Sabina Wolfson, Carlyn A. Patterson; Temporal Characteristics of the Straddle Effect (Buffy Contrast Adaptation) and Modeling with On-Off Neurons. Journal of Vision 2013;13(9):309. doi: https://doi.org/10.1167/13.9.309.
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INTRODUCTION. The appearance of a test pattern composed of two contrasts depends dramatically on the contrast of the adapt pattern immediately preceding it. If the test pattern’s contrasts straddle the adapt pattern’s contrast, the test pattern is extremely difficult for a human observer to perceive correctly. Our explanation of this psychophysical Straddle Effect has invoked a contrast comparison process that measures magnitude of contrast change but loses information about its sign. METHODS. Each adapt and test pattern was a regularly-spaced 2x2 grid of Gabor patches. The spatial characteristics of all Gabor patches in adapt and test patterns were the same on all trials. In the adapt pattern the four Gabor patches all had contrast 50%. In the test pattern, two of the four Gabor patches had one contrast, and two had another. The two test contrasts varied from trial to trial. The duration of the adapt pattern, the duration of the gap (a gray screen) between the adapt and the test pattern, and the duration of the test pattern were varied. The observer had to say whether the arrangement of the two different test contrasts formed horizontal or vertical stripes. RESULTS. The Straddle Effect was well developed with an adapt duration of about 50 ms. The effect was large with a gap duration of 0 ms and substantially diminished with a gap duration of about 50 ms. It was found for test durations varying from 12 ms to several seconds. CONCLUSION. These temporal results (along with spatial results reported last year) suggest the following: The contrast comparison process explaining the psychophysical Straddle Effect may result from On-Off neurons (neurons that respond transiently and positively to both increases and decreases in contrast) that have spatially-localized receptive fields. Preliminary modeling supports these suggestions.
Meeting abstract presented at VSS 2013
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