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Andrew Stockman; Seeing through a linear-nonlinear double-decker sandwich: the distorted world of Donald MacLeod. Journal of Vision 2019;19(8):32. https://doi.org/10.1167/19.8.32.
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One of the classical psychophysical methods applied with great effect by Donald MacLeod is the linear-nonlinear-linear sandwich model of the visual pathway in which the nonlinear sandwich-filling introduces distortion into a visual stimulus that can then be used to measure separately the characteristics of the preceding and succeeding linear stages. Following this tradition, we report experiments based on a linear-nonlinear-linear-nonlinear-linear double-decker sandwich model in the red-green chromatic pathway in which the first nonlinearity is assumed to be the half-wave rectification of signals into ON and OFF pathways and the second a later compressive nonlinearity. Together, these nonlinearities cause predictable and sometimes dramatic redward or greenward shifts in the mean colour appearance of harmonic combinations of sinusoidally-flickering M- or L-cone lights that are modulated around a mean yellow-appearing chromaticity. Combinations of (1) first and second, (2) second and third, (3) first, second and fourth, and (4) first, third and fourth harmonics were used in our experiments and all produced phase-dependent changes in the mean colour appearance that are predicted with remarkable accuracy by our model of the red-green chromatic pathway.
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