What is in a smile?


We distinguish genuine from fake smiles, even though we appreciate the polite sort of fake smile in many cases. I have thought it was a settled matter. Smiles are marked by the raising of the corners of the mouth and pulling them back. A broad smile (fake or real) opens the mouth by lowering the jaw. But only authentic smiles are marked by crow’s feet at the corners of the eyes. This is the Duchenne marker. Would you believe that it is just not that simple? The smile is a dynamic thing and research has mostly used static pictures to investigate smiles. A recent paper by Korb (citation below) examines dynamic smiles. Here is the abstract:

The mechanisms through which people perceive different types of smiles and judge their authenticity remain unclear. Here, 19 different types of smiles were created based on the Facial Action Coding System (FACS), using highly controlled, dynamic avatar faces. Participants observed short videos of smiles while their facial mimicry was measured with electromyography (EMG) over four facial muscles. Smile authenticity was judged after each trial. Avatar attractiveness was judged once in response to each avatar’s neutral face. Results suggest that, in contrast to most earlier work using static pictures as stimuli, participants relied less on the Duchenne marker (the presence of crow’s feet wrinkles around the eyes) in their judgments of authenticity. Furthermore, mimicry of smiles occurred in the Zygomaticus Major (smile muscle - positive), Orbicularis Oculi (Duchenne muscle - positive), and Corrugator muscles (frown muscle - negative). Consistent with theories of embodied cognition, activity in these muscles predicted authenticity judgments, suggesting that facial mimicry influences the perception of smiles. However, no significant mediation effect of facial mimicry was found. Avatar attractiveness did not predict authenticity judgments or mimicry patterns.”

In these experiments stronger smiles were found both more realistic and more authentic. This did not depend as much as previously thought on the eyes. The smile muscle action, the opening of the mouth and the lack of a frown in the brow were as important as the Duchenne marker. The subjects showed electrical activity in the muscles of their own faces mimicking the video being shown and whether the subject found the smile genuine could be predicted from this mimicry. The most clear mimicry was the combination of smile muscle and frown muscles. These two are correlated: in a smile the Zygomaticus is activated and the Corrugator is relaxed, while the opposite happens in a frown. The Masseter (jaw) muscle did not show mimicry. Since this is different from findings on static smiles, the question is raised whether smiles are judged by a different pathway when they are dynamic.

Embodiment theories propose that facial mimicry is a low-level motor process that can generate or modify emotional processes via facial feedback. However, other scholars favor the view that facial expressions are the downstream reflection of an internally generated emotion, and therefore play at best a minor role at a later stage of the emotion generation process. The main critique of the embodiment view is based on the observation that, in addition to their well-documented role in facial mimicry, the Zygomaticus and Corrugator muscles respond, respectively, to positive and negative emotional stimuli not containing facial expressions. However, the Orbicularis Oculi muscle is not clearly associated with positive or negative emotions and contracts, for example, during smiling (producing crow’s feet) as well as during a startle reflex in response to a sudden loud noise.”

This points to a low-level motor process because the Duchenne marker is mimicked in the Orbicularis muscle even though it is not actually a diagnostic for a smile. (It can occur in other situations and can be missing in some smiles.) It is more likely that the identification of a smile is due to mimicry than that mimicry is due to the identification of a smile. The authors suggest that this should be further investigated.

Nevertheless, the hypothesis that facial mimicry mediates the effect of smile characteristics on rated authenticity remains the most parsimonious one based on the fact that 1) facial mimicry is a costly behavior for the organism, 2) participants spontaneously mimicked the perceived smiles, and 3) this mimicry predicted ratings of authenticity. Importantly, the reverse hypothesis, i.e. that perceived authenticity may have caused participants’ facial reactions, seems less likely based on the finding that participants’ Orbicularis Oculi muscle was most activated in response to two types of smiles that contained the highest degree of the corresponding (marker), but resulted in very different ratings of authenticity.”

I hope that researchers will follow up on the idea that static and dynamic images of smiles are processed differently. Would there be clues in the order and timing of a smile unfolding that would point to its authenticity? If fake and genuine smiles are produced by different mechanisms then perhaps they would by quite different in their dynamics. Using avatars is a neat way to vary the dynamics of the muscle movements.

Korb, S., With, S., Niedenthal, P., Kaiser, S., & Grandjean, D. (2014). The Perception and Mimicry of Facial Movements Predict Judgments of Smile Authenticity PLoS ONE, 9 (6) DOI: 10.1371/journal.pone.0099194

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