Facial responsiveness to odours in normal and pervasively developmentally disordered children

The facial responsiveness of 10 mutic children with pervasive developmental disorder (PDD) and 10 normal (N) children matched for sex and chronological age were covertly videotaped while presented with a set of odours contrasted in hedonic valence. Hedonic ratings of the stimuli were obtained both from the group of N subjects and a panel of adults. Two methods were used to measure facial responses in the same subjects. The first method consisted in an analysis of facial movements with the Facial Action Coding System. Results show that PDD and N subjects displayed distinct action units in response to unpleasant odours. PDD subjects typically displayed muscular actions indexing negative experience, while N subjects showed more smiles. With the second method, odour-elicited facial behaviour was rated by a panel of observers, who were asked to judge whether the subjects were exposed a pleasant, neutral or unpleasant smell. The facial responses to unpleasant odours were classified more accurately in PDD than in N subjects. These findings suggest a functional ability to sense the hedonics attached to odours, but a deficit of socialization of hedonic facial displays in developmentally disordered subjects.