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Smile

Smiles are a prototypical facial expression of joy and positive emotion. A smile is formed when the zygomatic major muscle contracts and pulls the lip corners laterally upward. In addition to communicating happiness, smiles elicit positive engagement in others. This dynamic process of expressing and perceiving positive emotion contributes to the emergence of social competence in the developing child. This entry takes a life-span approach, considering research on the development and role of smiling in infants, children, and adults.

Infancy
First Smiles

Newborn infants tend to smile more frequently during drowsy and sleeping states, but smiles sometimes occur during nonsleep states during sensory stimulation. Over the first 2 months of life, infant smiling becomes increasingly linked to auditory and visual stimulation during nonsleep states—setting the stage for ...

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