The relationship between visual discomfort and cortical excitability in cone-opponent stimuli.

Increased colour contrast can induce visual discomfort, but there is little research on the effect of hue. Colour is processed via one or more information streams or channels. We hypothesized that hues which activate more than one channel would induce greater visual discomfort, as they will demand greater neural resources. Normally-sighted young observers made discomfort judgments of isoluminant stimuli of varying hue and contrast whilst EEG was recorded. As predicted, stimuli recruiting more than one channel were more uncomfortable, and this increased with contrast. Uncomfortable stimuli showed increased N2 event-related potentials and decreased alpha-band oscillations, potentially indicating increased neural excitability. This is evidence that increased neural responses are related to visual discomfort for chromatic stimuli. Furthermore, it suggests that the origins of visual discomfort are in early visual areas, when colour is represented in a cone-opponent space, rather than later areas where colour representation is determined by perceptual similarity.