Color saliency and attention change represented by neural processing in individuals with various color visions

There is a continuous diversity in human color vision. Minor color visions, such as dichromacy and anomalous trichromacy, occur in 4-8% of males, while most individuals are common trichromacy. Chromatic perception varies depending on the combinations of spectral sensitivities in the cones; however, later neural processing may also contribute to how colors are seen. In this research, we used EEG (electroencephalogram) to investigate the neural processes of people with different color visions during an attention-demanding oddball task using color stimuli with differences in saliency. The task required participants’ attention to detect and respond to a rarely presented deviant stimulus from a standard stimulus presented at high frequency. Two pairs of stimuli were prepared for a comparative analysis of P3, a component of the event-related potentials (ERPs), which indexes attention allocation. The pairs had a common standard color stimulus, green, with red or blue-green used as a deviant stimulus. All three colors were equally distant from the neutral grey of D65 in the CIE1976 u’v’ color space where the perceptual difference of common trichromacy was expressed as Euclidean distance. The deviant color stimulus in one pair was expected to have higher saliency than in the other pair and the higher saliency deviant was intended to be reversed between common trichromacy and M-cone-deviated deuteranomaly. P3 recorded from the deuteranomaly participants at the parietal region showed higher amplitude in response to the red deviant stimulus, reflecting increased attention allocation to the color with lower saliency. In contrast, the common trichromacy did not show differences in the amplitude or latency of P3, indicating no significant difference in saliency between the deviants regardless of the chromatic difference. These results suggest that individuals with minor color visions may compensate for the chromatic sensitivity in the retina through a later neural processing stage involving shifting attention allocation.