A neurological basis for visual stress and its treatment with coloured filters

The perceptual distortions and discomfort that some individuals experience when they read has a recent literature. A review of this literature leads to the conclusion that the distortions and discomfort can have their basis in an excitability of the visual cortex. Tinted lenses of an individually selected hue and saturation reduce the discomfort, possibly because the resulting change in the cortical distribution of activation avoids locally excitable tissue. The above conclusion is reached as follows. Images from nature, despite their heterogeneity, have in common certain statistical features that enable them to be encoded efficiently by the human visual system. Certain images that have an un-natural spatial and chromatic structure (including text) can be uncomfortable to look at. They can give rise to a large cortical haemodynamic response, consistent with indications from computational neurology that they are processed inefficiently. There are large differences between people in susceptibility to discomfort from images. These differences reflect differences in medical history. When the spatial and chromatic structure of images deviates maximally from those found in nature, susceptible individuals are liable to discomfort, migraine and/or seizures, a liability that individually coloured filters can sometimes reduce.