Colour desaturation in the periphery is explained by general mechanisms of contrast sensitivity and constancy

Colours appear less saturated in the visual periphery than in the fovea. We revisit this well-known phenomenon by characterising 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 colour and luminance in the periphery is affected similarly, governed by general laws of contrast sensitivity and constancy.