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Jens Christiansen, Anthony D'Antona, Steven Shevell; The locus of neural responses that determine color shifts induced by temporally-varying light. Journal of Vision 2009;9(8):308. doi: 10.1167/9.8.308.
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Introduction: Color appearance of objects is influenced by their surroundings. In chromatic induction, for example, the color appearance of a test field depends upon the chromaticity in the surround. If the surround slowly modulates between two chromaticities in time (say at 2 Hz), then a physically steady central test also is perceived to vary over time. With surround modulation above 3 Hz, however, the test field appears steady even though the surround modulation is salient. Surprisingly, a 6 Hz temporally-varying surround still influences the color appearance of the steady test field. The steady induced color shift in the test is very different than predicted from the time-average surround chromaticity, indicating the influence of a nonlinear neural mechanism. Purpose: This study addresses whether the neural response underlying the induced color shift is a steady (not time-varying) signal before binocular combination occurs. Method: The central test field was a physically steady annulus within a surround temporally modulating between two chromaticities at 6 Hz. Surrounds were modulated along one of four different chromatic lines in Macleod-Boynton color space, all with the same temporal average of equal-energy-spectrum “white”. On any given trial the modulation was along the same line in both eyes but haploscopic presentation allowed the surround modulations in the left and right eyes to be either in or out of phase. Rationale: If the monocular neural response underlying the induced color shift is a steady signal then an interocular phase difference should not change the monocular response from each eye and therefore not change the steady color shift. Results and Conclusion: Altering interocular phase caused large changes in the steady induced color shift. The phase dependency implies that induced steady color shifts from temporally-varying surrounds are due to a neural process that combines time-varying responses from each of the two eyes.
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