The Effect of Mouth-Opening on Recognition of Facial Expressions in the NimStim Set: An Evaluation from Chinese College Students

Based on the physical facial features available to visual perception, mouth features play an essential role in perceiving and recognizing facial expressions, but they have not been as widely studied as eye features. The NimStim set provides a more extended and popularized version of the basic expressions with open mouth and closed mouth. In this study, 209 Chinese college students were recruited to identify and evaluate the feelings of seven facial expressions in the NimStim, and we explored the influence of open mouth on gender and cultural differences. The results were as follows: (1) The open mouth did not always correspond to a higher recognition rate. The neutral and sad expressions had a higher correct rate with the mouth closed, and the happy expression had a higher correct rate with the mouth slightly open. (2) In addition to neutral expressions, females showed an advantage in recognizing emotional expressions. The female advantage in recognizing sad expressions was more prominent in the closed-mouth, and in recognizing fear (open mouth) was more prominent when the actor was male. Our results advanced the role of mouth opening and closing in facial expression perception. We also revealed that the observer's gender affects the facial expression perception in Chinese culture.

Automated summary

Based on physical facial features, mouth features play a vital role in recognizing facial expressions. This study investigated the impact of different mouth states in NimStim on emotion recognition and explored the influence of gender and culture on facial expression perception. The results showed that the relationship between mouth state and recognition rate is not straightforward, and gender and culture also affect emotion recognition.