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Updated: May 25, 2026

Visualizing Visual Adaptation
Published on: April 24, 2017
Quantal and non-quantal color matches: failure of Grassmann's laws at short wavelengths
Joel Pokorny1, Vivianne C Smith, Jun Xu
1Visual Sciences Center, The University of Chicago, 940 East 57th Street, Chicago, Illinois 60637, USA. j‑pokorny@uchicago.edu
Abstract:
Previous studies of color matching found that Grassmann's laws are not obeyed in the short-wavelength region when the method of maximum saturation matching is compared with Maxwell matching. The first experiment evaluated whether the discrepancy might be due to a discrimination matching range asymmetry around either the saturated or desaturated matches and concluded that asymmetry is not the dominant factor. The second and third experiments were designed to evaluate postreceptoral mechanisms. The results pointed to the conjunction of three factors as being the principal cause of the failures of Grassmann's laws: the spatial inhomogeneity of the macular pigment distribution, the spatially dissimilar L/M-and S-cone distributions, and a change in the weightings of postreceptoral mechanisms mediating S-cone chromatic and L/M-cone luminance discriminations.
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