Luminance and chromaticity discrimination sensitivities right after an abrupt decrease in background luminance

When we enter a dark place, such as a tunnel, from a bright exterior, our visual sensitivities take some time to adapt to lower light levels. However, there have been few reports on how quickly luminance and chromaticity discrimination sensitivities recover in this situation. This study aims to quantify the time course of discrimination sensitivity for luminance and chromaticity directions after an abrupt decrease in background luminance. In each trial, the background luminance was decreased from 100 to 1 cd/m2. Subsequently, one target and three reference stimuli of different colors were presented under four stimulus‐onset asynchrony (SOA) conditions. The participants discriminated the target stimulus from reference stimuli. The results showed that discrimination sensitivity was the lowest right after the background luminance changed and gradually improved with SOAs. The sensitivity decreases differed across color directions, with the greatest decrease in luminance, a moderate decrease in S−(L + M), and a negligible change in L−M. However, statistically significant differences were observed only between luminance and L−M, suggesting that the sensitivity decrease after the abrupt decrease in background luminance did not significantly differ between the chromaticity directions. We speculate that these results stem from the interaction between chromatic perception and luminance adaptation, and possibly from rod intrusions.