Effect of skin colors due to hemoglobin or melanin modulation on facial expression recognition

Facial color is thought to contribute to the perception of emotional expression. Previous studies on facial recognition have shown that reddish and bluish faces enhance the perceptions of anger and sadness, respectively. However, the effect of facial color on the recognition of facial expressions in the range of natural skin colors remains unexplored. In this study, we examined the effect of natural skin color changes on the perception of facial expressions of anger, sadness, and happiness. We used five skin color conditions for each facial expression: standard, and hemoglobin or melanin decrease/increase (H-, H+, M-, and M + ). In the experiment, we used images of different facial expressions ranging from neutral to maximum intensity. Observers judged whether a face stimulus was perceived as "angry" ("happy" or "sad") or "not angry" ("not happy" or "not sad"). The results showed that H+, M+, H-, and M- enhanced the perception of anger and happiness, respectively. However, the change in the perception of sadness due to these modulations was small. These results suggest that the range of natural facial colors by hemoglobin and melanin modulation affects facial expression recognition. We further consider the possibility that these results could be partially explained by the lightness of the stimulus.