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.

视觉不适（visual discomfort）与视觉图像的统计规律紧密相关。亮度对比度对视觉不适的影响已得到充分阐释，可通过自然刺激高效编码（efficient coding）理论进行框架性分析，并与代谢需求（metabolic demand）建立关联。尽管色彩在人类与自然环境的交互中发挥着重要作用，但色彩对视觉不适的影响却较少受到学界关注。
本研究立足于已确立的视觉不适与空间色度（chromaticity）差异之间的关联展开。我们对图像中的局域色度差异进行平均化处理，结果表明，该平均值可作为图像引发视觉不适的良好预测指标，能够解释亮度变化未覆盖的部分方差（variance）。研究发现，相较于自然场景中的典型情况，易引发不适的刺激的局域色度差异显著更高，但在少数特定罕见场景中除外，例如彩色果实与植被枝叶形成的色彩对比场景。
总体而言，本研究揭示了视觉生态学（visual ecology）与视觉不适之间的全新关联：当适应性感知机制受到自然中罕见的特定类别刺激过度刺激时，便会产生视觉不适。