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Hannah Smithson, Angela Bourke, Qasim Zaidi, John Mollon, Andrew Stockman; Three ways to find a tritan line. Journal of Vision 2004;4(11):83. doi: 10.1167/4.11.83.
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We compare three methods of locating a tritan line. Method I exploits ‘transient tritanopia’ (Mollon & Polden, 1975). If the abrupt offset of a yellow field produces a selective loss of sensitivity in the S-opponent mechanism, the direction in colour space along which the loss of sensitivity is greatest should locate the tritan line. Method II uses a blue adapting field to elevate selectively S-cone detection thresholds (e.g. Webster, DeValois & Switkes, 1990). Method III is a performance version of the minimally distinct border method (Tansley & Boynton, 1976). Our stimulus comprises two coloured areas that are separated by a jagged (sawtooth) border. Observers are required to discriminate between sawteeth that are inverted or non-inverted in spatial sign. Since the task requires resolution of high spatial frequencies, performance should be poorest when the border is defined only by the S-cone signal.
We test the extent to which Methods I and II are dependent on the spectral composition of the adapting field. Estimates from both methods may be biased by preferential adaptation of the L- or M-cones. Of the two methods, Method I seems less influenced by moderate changes in the L:M component of the adapting field. Importantly, all three methods, if properly applied, converge to a common estimate of the tritan line for a given observer and retinal eccentricity. We discuss the limitations and relative merits of each method.
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