Abstract
Happiness and joy involve feelings of positive engagement which are prototypically expressed through the face, voice, and body. Joyful smiles tend to be strong and involve both eye constriction (the Duchenne marker) and mouth opening. Through approximately 2 months of age, joyful expressions are primarily rooted in physiological arousal. Positive emotional expressions then quickly become more social, occurring in face-to-face interactions with caregivers as infants increasingly derive psychological meaning from individuals and events. Beginning in the second half of the first year of life, infants’ expressions of positive emotion are increasingly incorporated into patterns of intentional communication. Between 1 and 2 years of age, positive expressivity is increasingly responsive to parental affective cues during pretense play. Preschoolers’ between 2 and 5 years of age utilize specific forms of positive emotion expressions to foster affiliation with their peers. By 8 years of age, children voluntarily control their expressions of positive emotion depending on the interpersonal context. These early expressions of joy are associated with later social competence, including reduced behavioral inhibition and reticence in reaction to novelty, compliance with parental requests, tolerance of new experiences, and attachment security. Further, positive expressivity is also linked to later life outcomes, primarily life satisfaction and overall well-being in adulthood. Positive emotion expression varies as a function of gender as well as cultural differences in the emotional significance and perceptions of positive expressions. Finally, the development of joyful expressivity is differentially sensitive to a variety of risk conditions, including maternal depression, prematurity, infant blindness, Down syndrome, and autism spectrum disorder.