What is characterized by an infant evoking a smile in response to a human face?

The phenomenon of an infant smiling in response to a human face is known as a social smile. This response typically emerges around two months of age and signifies the infant's developing social awareness and the beginning of social interactions. Infants are naturally inclined to engage with caregivers and others, and the smile in response to faces shows the infant's ability to recognize and react to social stimuli. This behavior is a crucial aspect of early human development, as it lays the foundation for bonding, emotional connections, and social communication.

In contrast, the other options describe different behaviors that, while significant in their own right, do not capture this particular interaction. A frown in the presence of a stranger indicates discomfort but does not involve positive social engagement. A cry when hungry reflects the infant's basic needs rather than social interaction. A laugh during playtime illustrates enjoyment but is not specifically tied to the recognition of a human face. Thus, the response characterized by an infant evoking a smile in response to a human face is distinctly captured by the first option.