During the COVID-19 pandemic, wearing face masks is an important strategy to prevent people from infection, allowing people to find a balance between maintaining social interaction and keeping social distancing. Since face mask might disrupt information processing of social cognition, it could lead to less functional connectivity of occipital face area, fusiform face area, and superior temporal sulcus which interrupted the development of medial prefrontal cortex (MPFC) for mentalizing. However with better executive function (EF) people could process facial stimuli more efficiently. The objective of this study is to examine the effect of wearing face masks on preschoolers' facial emotion recognition, and the factors which might affect the development of facial emotion recognition.

In this study, preschoolers (N=44, 24 boys and 20 girls, aged 3 to 5 years-old) recruited from the community were asked to identify the emotions expressed in the 36 stimulus photos, each randomly presented with six emotion (happy, sad, angry, surprised, fearful, and disgusted). The total face stimulus photos were 2 (face sex) × 6 emotions × 3 facial features (full face, presenting upper counterparts of face with face mask covering the mouth, and presenting lower counterparts of face with hat covering the eyes). The EF of preschoolers and their parent were also evaluated to examine whether EF could predict the correct score of facial emotion recognition.

It was found that the correct score of emotion recognition increased with age. The recognition with full face feature were better than with upper feature and lower feature. When recognizing happy and disgust, participant tended to use lower features. When recognizing sad and angry, participant tended to use upper features. The EF of preschoolers could predict the correct score of emotion recognition. The EF of parents could predict the preschoolers' correct score of positive emotion recognition.

The ability of facial emotion recognition evolved rapidly in preschool age with the accumulation of social interaction experience and improved the development of auditory and visual subcortical cortex and the connectivity of MPFC. This study examined the emotion recognition ability of preschoolers and found that the face features preschoolers used to recognized emotion were consist with previous study. However, when the presenting stimulus were covered by face mask or hat, it was more difficult for preschoolers to recognizing emotion which would result in difficulty of understanding the social context and development of MPFC for mentalizing. In this study, it was found that preschooler's with better EF could be more efficiently recognizing facial emotion. Also, parents with better EF showed more positive emotion in daily life which lead to their children more sensitive to positive facial emotion.