Visual discomfort and variations in chromaticity in art and nature

Visual discomfort is related to the statistical regularity of visual
images. The contribution of luminance contrast to visual discomfort is
well understood and can be framed in terms of a theory of efficient coding
of natural stimuli, and linked to metabolic demand. While colour is
important in our interaction with nature, the effect of colour on visual
discomfort has received less attention. In this study, we build on the
established association between visual discomfort and differences in
chromaticity across space. We average the local differences in
chromaticity in an image and show that this average is a good predictor of
visual discomfort from the image. It accounts for part of the variance
left unexplained by variations in luminance. We show that the local
chromaticity difference in uncomfortable stimuli is high compared to that
typical in natural scenes, except in particular infrequent conditions such
as the arrangement of colourful fruits against foliage. Overall, our study
discloses a new link between visual ecology and discomfort whereby
discomfort arises when adaptive perceptual mechanisms are overstimulated
by specific classes of stimuli rarely found in nature.