Variations in face experiences during the COVID-19 pandemic affect infants' preference for their mother's face

The Coronavirus disease 2019 pandemic has significantly altered infants' social environments. In Japan, people continued to wear face masks outdoors for approximately three years following the onset of the pandemic. Consequently, most infants born during this period have limited exposure to unmasked faces. However, how such changes in face experience may influence the development of face processing during infancy remains unclear. In the present study, we investigated visual preferences for mothers' faces versus unfamiliar female faces in 5-8-month-old infants born during the pandemic in three regions of Japan (Tokyo in Experiment 1 and provincial cities in Experiment 2). Infants' preferences for their mothers' faces were evaluated under two conditions: when both faces were unmasked (unmasked condition) and when both wore face masks (masked condition). Additionally, parents completed questionnaires reporting their infant's exposure to unmasked faces in daily life. Group-level analysis showed that infants in provincial cities significantly preferred their mothers' faces under both masked and unmasked conditions. By contrast, infants in Tokyo showed a significant preference for their mothers' faces only in the masked condition. Moreover, individual-level analyses revealed that infants with greater exposure to unmasked faces were more likely to prefer their mothers in the unmasked condition. These findings suggest that infants' daily visual experiences, particularly with unmasked faces, may modulate their developing preferences for their mothers' faces, highlighting the impact of social context on early face processing.