Effect of cone-opponent modulation on visual discomfort from chromatic flicker

Visual patterns with large shifts in chromaticity can be perceived as uncomfortable and may even trigger photosensitive epilepsy. In the temporal domain, not only does large chromatic contrast tend to increase discomfort, but red flicker also appears to evoke strong aversion. The mechanisms underlying this red-specific discomfort, however, remain unclear. To address this issue, the present study measured discomfort ratings for two-color alternating stimuli defined in the MB-DKL cone-opponent space, in which the magnitudes of modulation along the L/(L + M) and S/(L + M) axes were systematically manipulated. We found that modulation along the L/(L + M) axis showed a positive correlation with discomfort ratings, whereas modulation along the S/(L + M) axis also predicted discomfort but with a comparatively weaker effect. We also replicated previous findings that greater temporal chromatic contrast, quantified in a uniform color space, was associated with increased discomfort. Importantly, the relationship between L/(L + M) modulation and discomfort remained robust even when chromatic contrast was controlled. These results suggest that visual discomfort from temporal chromatic variation involves multiple stages of color processing. Specifically, the aversion to red flicker may originate at early stages of cone-opponent processing, prior to the formation of categorical red perception.