The perception of smiling and its experiential correlates in three-month-old infants.

We studied individual differences in 3-month-olds' perceptions of smiling and the experiential correlates of those differences. In the laboratory, infants saw a graduated series of smiles that grew in intensity of expression. As a group, 3-month-olds preferred increasingly intense expressions of smiling, but individually they showed different growth rates of preference across the smiling series. Further, infants' preferences related to their home experiences: Infants who showed greater sensitivity to smiling had mothers who more frequently encouraged attention to themselves when they were smiling and their infants were looking at them. Infant discrimination within and between categories of facial expression and the relative strengths of association between different kinds of naturally occurring experiences and infant perceptual sensitivity are discussed.