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R. D. Beer, D. I. A. MacLeod; Afterimage appearance and adaptation. Journal of Vision 2001;1(3):458. doi: 10.1167/1.3.458.
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The study of adaptation commonly requires asymmetric matches, where the test and comparison stimuli are viewed in obviously different contexts. This makes matching more subjective. Whittle and others have made effective use of a haploscopic display in which the different backgrounds of the test and comparison stimuli are binocularly fused. We have been exploring an alternative technique for investigating the dynamics and quantitative properties of visual adaptation. We generate adapting fields that have broad Gaussian spatial profiles, embedded in a uniform surround on one or other side of the fixation point. Under steady fixation, the adapting field fades completely over several seconds, creating a subjectively uniform field in which we present, generally simultaneously, two similarly profiled incremental or decremental flashes: the test stimulus, superimposed on the adapting field, and the comparison stimulus, superimposed on the uniform surround. Phenomenally, test and comparison stimuli appear against the same surround, despite their physically different adapting conditions. Unlike typical asymmetric matches, the matches are subjectively unambiguous. After complete fading, test and comparison stimulus match in brightness when they are the same multiple of the incremental (or decremental) threshold measured on their respective backgrounds. When matches are made before the slow fading process is complete, the test stimuli assume a brightness that is not strictly determined by the incremental or decremental temporal transient, but reflects SOME contribution of the slowly fading subjective brightness of the Gaussian background. Both before and after fading, however, the sensitivity loss appropriate to the difference in background intensity is reflected in the matching of the temporal transients.
Surfaces, 3D Shape.
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