Color Desaturation in the Periphery is Explained by General Mechanisms of Contrast Sensitivity and Constancy

Abstract Colors appear less saturated in the visual periphery than in the fovea. We revisit this well-known phenomenon by characterizing parafoveal perceived contrast as a function of size. Observers (n = 20) matched perceived contrast of a parafoveally presented comparison disc (2° -0.33°) to a standard 2° disc. For chromatic stimuli, desaturation increased with decreasing size. Unexpectedly, a similar amount of desaturation occurred for luminance-defined discs, once their perceived contrast was adjusted to match the standard chromatic discs. Desaturation was reduced as standard stimulus contrast increased, in line with contrast constancy theory, which predicts constant appearance for stimuli that are sufficiently distant from threshold. Since chromatic contrast sensitivity is reduced away from the fovea, contrast constancy is unachievable within the monitor gamut. In conclusion and somewhat counter-intuitively, the appearance of color and luminance in the periphery is affected similarly, governed by general laws of contrast sensitivity and constancy. Public Significance Statement In the early stages of visual signal processing, color and luminance (achromatic) information are separated. If we overgeneralize on the basis of such early separation, we may conclude that the desaturated appearance of small and peripherally presented color stimuli is specific to color processing mechanisms. Here we show that this is not the case and that chromatic and achromatic stimuli are processed similarly when presented in the periphery, implying that such processing is governed by more general contrast-processing mechanisms. Our work provides the basis for a better understanding of how the visual system builds a unified experience of color appearance across chromatic and achromatic dimensions from the information on contrast present in the image. Competing Interest Statement The authors have declared no competing interest. Footnotes a.rozman{at}sussex.ac.uk Funding: AR was funded by a BBSRS EASTBIO DTP PhD studentship (BB/M010996/1) to conduct her research under the supervision of JM. Updates made to the introduction and new analyses (bayesian statistics) added.