Emotion in the infant's face: insights from the study of infants with facial anomalies.

Darwin viewed "experiments in nature" as an important strategy for elucidating the evolutionary bases of human emotional expressions. Infants with craniofacial anomalies are of special interest because morphological abnormalities and resulting distortions or deficits in their facial expressions could make it more difficult for caregivers to read and accurately interpret their signals. As part of a larger study on the effects of craniofacial anomalies on infant facial expression and parent-infant interaction, infants with different types of craniofacial conditions and comparison infants were videotaped interacting with their mothers at 3 and 6 months. The infants' facial expressions were coded with Baby FACS. Thirty-seven slides of 16 infants displaying 4 distinctive infant expressions (cry face, negative face, interest, and smile) were rated by 38 naive observers on a 7-point scale ranging from intense distress to intense happiness. Their ratings were significantly correlated with ratings based on objective Baby FACS criteria (r > 0.9 in all infant groups). A 4 (infant group) x 4 (expression category) ANOVA showed a significant main effect for expression category, F(3) 5 71.9, P 5 0.000, but no significant effect for infant group or group 3 expression interaction. The observers' ratings were thus highly "accurate" in terms of a priori Baby FACS criteria, even in the case of infants with severely disfiguring facial conditions. These findings demonstrate that the signal value of infant facial expressions is remarkably robust, suggesting that the capacity to read emotional meaning in infants' facial expressions may have a biological basis.