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Arthur G. Shapiro, Laura A. Baldwin, Qasim Zaidi; Time course of L-M system adaptation to simple and complex fields. Journal of Vision 2002;2(7):142. doi: 10.1167/2.7.142.
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Shapiro, Beere, and Zaidi (2001) examined the response of the L-M system as adaptation shifted from one chromaticity on an L-M line to another. The steady state results could be described by a post-opponent subtractive stage before a non-linear response function, but the shapes of the transitory threshold curves could not be explained by early multiplicative or subtractive adaptation, and were suggestive of the effects of higher mechanisms involved in adaptation to color modulations. In order to isolate the effects of the higher adaptation processes, we compare changes in response following adaptation to uniform chromatic fields to changes measured following adaptation to spatio-temporally complex fields. Lights were restricted to an L-M cardinal axis, with end-point chromaticities R and G and mid-point W. Difference thresholds were measured from probes on nine flashed backgrounds during adaptation to a uniform field with chromaticity R, G, or W, and after RG adaptation (i.e. adaptation to a field of 0.3 deg squares with chromaticities randomly assigned to R or G every 0.1 sec; the space and time averaged chromaticity of the field equaled W). We measured the same probe-threshold curves after 0.1, 0.25, 0.5, 1.0 and 2.0 sec of shifting adaptation from G to W, R to W, or from RG temporal alternation to W. Following steady R, G, and W adaptation, the probe-flash threshold curves form identical V shapes centered at or near the adapting chromaticity. During the shift from R to W and G to W the curve flattens before forming a V with a minimum at W. Following RG adaptation the threshold curves are flatter than following steady adaptation. The data provide an estimate of the effects and time course of higher-level adaptation.
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