On the assumption that the ability to discriminate facial expressions has adaptive value to infants during early social exchanges, ethologically based theorists have argued that this ability is innate. Guided by this perspective, we investigated the ability of infants, 4-6 months old to recognize and discriminate facial expressions of anger, fear, and surprise. Results obtained with an infant-controlled habituation-recovery procedure showed that infants both discriminated and recognized these expressions when portrayed by several adult female models. In addition, infants spent more time looking at expressions of anger and surprise than at fear expressions. These results suggest that infants can abstract configurations of features that give affective meaning to facial expressions. It is suggested that the differences in habituation to each expression might be the result of their distinct functional signification for the infant.
In this study, facial asymmetry in chimpanzees was assessed using a technique that has traditionally been implemented in human studies. Image composites made of each half of chimpanzees' facial expressions were presented to humans with and without chimpanzee experience. The group of subjects with chimpanzee experience considered composites made of the left side of the chimpanzee faces as the most emotionally intense for the emotional categories of play, silent bared-teeth, scream face, and a neutral category. On the other hand, left-left composites were not consistently judged by subjects with and without chimpanzee experience as the most similar to the whole original face, which might be explained as the result of an attentional bias in the human observers towards the right side of the chimpanzee expressions. Furthermore, responses given by subjects with and without chimpanzee experience were highly correlated, which indicates that the two groups of humans perceived the chimpanzee facial expressions in a similar fashion. The finding of left-sided asymmetries in these chimpanzees' facial expressions suggests a right hemisphere asymmetry in the production of emotions in this species and it is consistent with results reported in human and other nonhuman primates.
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