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Patrick Monnier, Lucy J. Troup; Classical definitions of chromatic induction are inadequate for induction with S-cone patterned backgrounds. Journal of Vision 2006;6(6):241. doi: 10.1167/6.6.241.
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BACKGROUND/PURPOSE: Inducing patterns composed of circles selectively stimulating the S cones can induce large color shifts. These shifts were previously accounted for by chromatic assimilation to nearby inducing light and simultaneous contrast from distal light (Monnier & Shevell, 2004). Classically, assimilation and contrast are defined as shifts “toward” and “away” from the inducing chromaticity, respectively. In this study, we show that these classical definitions of induction are inadequate to describe shifts observed with S-cone patterns.
METHODS: Chromatic induction was measured with asymmetric matching. Shifts were measured for test ring chromaticities that produced: (1) intermediate levels of S-cone stimulation compared to the inducing circles; (2) either lower or higher levels of S-cone stimulation than the inducing circles. According to the classical definitions of chromatic induction, shifts for test chromaticities outside the inducing chromaticities should be much reduced, as assimilation and contrast should tend to cancel.
RESULTS: As previously, the appearance of a test ring of intermediate S-cone stimulation shifted toward the nearby, and away from, distal inducing light. Surprisingly, the direction and the magnitude of the color shifts were relatively constant even when the test ring chromaticity was outside the range of inducing chromaticities. The measurements suggest the classical definitions of chromatic induction are inadequate here as the shifts were not always ‘toward’ and ‘away’ from the nearby and distal light.
CONCLUSIONS: Color shifts with S-cone patterns were relatively independent of the test ring chromaticity. This runs counter to an interpretation based on classical definitions of induction.
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