Abstract
Smiles that vary in muscular configuration also vary in how they are perceived. Previous research suggests that “Duchenne smiles,” indicated by the combined actions of the orbicularis oculi (cheek raiser) and the zygomaticus major muscles (lip corner puller), signal enjoyment. This research has compared perceptions of Duchenne smiles with non-Duchenne smiles among individuals voluntarily innervating or inhibiting the orbicularis oculi muscle. Here we used a novel set of highly controlled stimuli: photographs of patients taken before and after receiving botulinum toxin treatment for crow’s feet lines that selectively paralyzed the lateral orbicularis oculi muscle and removed visible lateral eye wrinkles, to test perception of smiles. Smiles in which the orbicularis muscle was active (prior to treatment) were rated as more felt, spontaneous, intense, and happier. Post treatment patients looked younger, although not more attractive. We discuss the potential implications of these findings within the context of emotion science and clinical research on botulinum toxin.
Highlights
Among all communicative signals, smiles are one of the most recognizable facial expression, with a visual pattern that is detectable over long viewing distances (Smith and Schyns, 2009; Krumhuber et al, 2019)
There were no significant associations between treatment and any other measured emotions
All pre-treatment photographs depicted patients displaying Duchenne smiles. These smiles were rated as being happier, more felt, more spontaneous, and more intense than those posed by the same patients under the same conditions and instructions in post-treatment photographs
Summary
Smiles are one of the most recognizable facial expression, with a visual pattern that is detectable over long viewing distances (Smith and Schyns, 2009; Krumhuber et al, 2019) In morphological terms, they can be defined by the activation of the zygomaticus major muscle—a facial muscle which pulls the lip corners upwards and away from the mouth (Ekman, 1989). Other smiles are deliberately displayed in the absence of an underlying positive affect, for example, to signal politeness, affiliation, or feigned cooperation (Ekman, 1989; Rychlowska et al, 2017) Due to their voluntary nature, those latter expressions are typically described as posed, social, or polite smiles. What is the distinction between spontaneous and posed signals reflecting such disparate functions?
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