Relationship between brightness perception and skin color influenced by experimental method

Facial brightness perception is affected by skin color. It was reported that reddish skin was matched with a higher lightness scale stimulus than yellowish skin among Japanese observers. However, this trend is inconsistent among Thai, Korean, Chinese, and European observers, implying the influence factors, such as ethnicity, environment, and judgment criteria. In this study, we investigated the influence of the experimental method on facial brightness perception using test stimulus images with constant lightness and different hue angles. We examined two instructions ("Appearance match" vs. "Brightness match") and the scale stimulus for matching (a uniform color patch vs. a face image). We further conducted an impression evaluation experiment of the whole face. The matching results from the Japanese showed a similar trend in both instructions and scale stimuli under most conditions, suggesting that matched brightness is not influenced by instruction and the complexity of scale stimuli. The impression evaluation results were similar for Thai, Japanese, and Chinese observers, with reddish faces being evaluated with higher scores in brightness. Our findings suggest the influence of experimental methods on facial brightness judgment. The holistic judgment of facial brightness would be universal among different East Asian groups, at least for the range of variation in skin color we used. The skin color of the face affects the perceived brightness at the same metric lightness. However, the effect is influenced by stimuli and experimental methods. image