All Smiles are Not Created Equal: Morphology and Timing of Smiles Perceived as Amused, Polite, and Embarrassed/Nervous.

We investigated the correspondence between perceived meanings of smiles and their morphological and dynamic characteristics. Morphological characteristics included co-activation of Orbicularis oculi (AU 6), smile controls, mouth opening, amplitude, and asymmetry of amplitude. Dynamic characteristics included duration, onset and offset velocity, asymmetry of velocity, and head movements. Smile characteristics were measured using the Facial Action Coding System (Ekman, Friesen, & Hager, 2002) and Automated Facial Image Analysis (Cohn & Kanade, 2007). Observers judged 122 smiles as amused, embarrassed, nervous, polite, or other. Fifty-three smiles met criteria for classification as perceived amused, embarrassed/nervous, or polite. In comparison with perceived polite, perceived amused more often included AU 6, open mouth, smile controls, larger amplitude, larger maximum onset and offset velocity, and longer duration. In comparison with perceived embarrassed/nervous, perceived amused more often included AU 6, lower maximum offset velocity, and smaller forward head pitch. In comparison with perceived polite, perceived embarrassed more often included mouth opening and smile controls, larger amplitude, and greater forward head pitch. Occurrence of the AU 6 in perceived embarrassed/nervous and polite smiles questions the assumption that AU 6 with a smile is sufficient to communicate felt enjoyment. By comparing three perceptually distinct types of smiles, we found that perceived smile meanings were related to specific variation in smile morphological and dynamic characteristics.