FORMS AND SOCIAL SIGNAL VALUE OF SMILES ASSOCIATED WITH PLEASANT AND UNPLEASANT SENSORY EXPERIENCE

Episodes of facial displays involving the zygomatic action (AU12: lip corner pulling or smiling) were selected from a large sample of childr en (n = 95) exposed to pleasant and unpleasant odours in the presence of an unfamiliar person in order to investigate potential differences in morphological, temporal patterning and social signal value of smili ng. In a first experiment using the facial action coding system (FACS: EKMAN & FRIESEN 1978), a considerable morphological flexibility of sm ites was observed in relation to the subjects' hedonic experience. The facial configurations of smiling smiling were formed by a number of a ctions in the upper (AU 4: brow lowering), middle (AU 9: nose wrinklin g) and lower face (AU 14: dimpling AU 15: lip corner depressing, AU 17 : chin raising, AU 23: lip tightening) and the mouth was more often 'c losed' in response to unpleasant odours. When exposed to pleasant odou rs, zygomatic action co-occurred more frequently with an opening of th e mouth (AUs 25, 26, 27) or with a raising of the cheeks (AU 6). An an alysis of the temporal patterning of zygomatic actions showed that the y occurred more rapidly, dropped off the face less abruptly with a ste pped decrease, were less smooth, and were often associated with shorte r gazes directed toward the examiner in response only to unpleasant od ours. These findings suggested that a number of subjects might exert s ome control on their smiling while confronted with a presumed social c onstraint, namely the smelling of unpleasant odours in the presence of an unfamiliar person. In a second experiment, the communicative value of smiling was investigated in a real-time projection of 10 variants of smiling to a panel of receives (n = 52). The Duchenne smile (AU 6 12 + 25) and smile with lips opening (12 + 25) provided more accurate information about the hedonic valence of the inhaled odour than did t he other types of smiling. In contrast, the perceived valence of the f acial displays simultaneously combining zygomatic action with muscular actions of the lower face (AUs 15, 17, 23) appeared more difficult to discriminate by untrained receivers. It was hypothesized that the sen ders displayed some forms of smiling possibly to mask their responsive ness to unpleasant odours in signalling ambiguous or incorrect informa tion about their internal state to a recipient.