Individual Differences in Color-Induced Visual Discomfort Reveal a Pupillary Dissociation Across Stimulus Dimensions

Visual discomfort (VD) is influenced by both spatial structure and chromatic context. Striped patterns are well-established triggers of discomfort and autonomic responses. In previous work, we showed that higher spatial frequencies and larger patterned areas elicit stronger pupillary constriction and greater discomfort, and that individuals with higher overall discomfort show shallower maximum constriction. The present study examined whether similar relationships appear when spatial structure is held constant, measured background luminance is kept within a narrow range, and the chromatic background varies. Participants viewed black horizontal stripes on 12 near-isoluminant colored backgrounds. The CIE76 color difference ({Delta}E) ranged from 36 to 112 and was indexed as the CIELAB distance from the black stripe pattern. Pupil size was continuously recorded and discomfort ratings were collected after each trial. Across the colored backgrounds, more uncomfortable stimuli evoked stronger pupil constriction, even though luminance was held nearly constant. As in our spatial-frequency study, this stimulus-level increase did not translate into stronger constriction among observers reporting higher overall discomfort: participants who rated the stimuli as more uncomfortable overall showed shallower constriction. This pattern was captured by the maximum-constriction response, which differentiated high-from low-discomfort observers and was significantly associated with individual discomfort ratings. Together with our previous findings, the results suggest that pupil responses scale along the tested stimulus axis, whereas individuals reporting greater visual discomfort exhibit less pronounced maximum constriction. HighlightsO_LIChromatic background modulated discomfort and pupil responses at similar luminance. C_LIO_LIAcross backgrounds, higher discomfort ratings tracked stronger pupil constriction. C_LIO_LIAcross observers, higher mean discomfort tracked weaker pupil constriction. C_LIO_LIThis two-level dissociation recurs across spatial and chromatic manipulations. C_LIO_LIPupillometry may complement subjective reports of visual discomfort. C_LI