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Patrick Monnier, Steven K. Shevell, Erica J. Young; Induction from a chromatic pattern that cannot be seen. Journal of Vision 2005;5(8):98. doi: https://doi.org/10.1167/5.8.98.
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BACKGROUND: Patterns with regions alternating between two chromaticities can induce large shifts in color appearance (Monnier & Shevell, 2003, Nature Neuroscience). Reliable shifts occur even with patterns having S-cone contrast of only 10%. Here we consider whether an inducing pattern with contrast so low that it cannot be perceived still induces color shifts.
METHODS: In a preliminary experiment, threshold for S-cone contrast in a pattern was measured by a 2AFC staircase procedure. A non-signal interval contained 2 identical uniform achromatic backgrounds, presented side by side. A signal interval contained one uniform achromatic background and one patterned background (3 cpd) with inducing circles alternating between higher S-cone (toward purple) and lower S-cone stimulation (toward lime). In the main experiment, a centrally located test ring was inserted in all the backgrounds. The chromaticity of the test was chosen from previous work that showed strong induction from high contrast S-cone patterns. The task was to choose the interval in which the two backgrounds were different.
RESULTS: With the test ring in the patterns, each of 4 observers could reliably distinguish the signal from the non-signal interval at an S-cone contrast too low to be detected in the preliminary experiment without the test ring.
CONCLUSIONS: A test ring within an inducing pattern with S-cone contrast can be distinguished from a test ring within a uniform background, even when contrast in the pattern is below threshold. The results are consistent with an induced color shift from a chromatic pattern that cannot be perceived.
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