More what Duchenne smiles do, less what they express

The paper by Sheldon and colleagues is part of the body of literature that tries to disambiguate the function of a particular facial movement regarding emotional and social processes in humans: the concurrent activation of the zygomaticus major and orbicularis oculi muscle. The resulting visible change in facial appearance is often referred to as Duchenne Smile (DS) in honor of Duchenne de Boulogne, who published in 1862 a series of photographs of facial behavior triggered by external electrical stimulation of individual muscles (Duchenne, 1862/1990). Some authors have argued that DS are authentic because they are difficult to produce voluntarily. Indeed, the idea of reliable facial muscles (i.e., the orbicularis oculi muscle as Duchenne marker) unique to genuine emotional experiences that are difficult to deliberately control was reinforced in the late 20th century, particularly via the work of Paul Ekman and his colleagues (e.g., Ekman, 1990; Ekman, Davidson, & Friesen, 1990). A popular notion at the time was the idea of facial affect programs that trigger prototypical facial configurations corresponding to the basic six emotions. In this logic, the DS is a neurobiologically hard-wired (i.e., diagnostic, spontaneous) marker of enjoyment said to activate only during felt affect. By contrast, smiles without the Duchenne marker are thought of as false, fake, or dishonest, and lacking genuine positive affect (Frank, Ekman & Friesen, 1993). We would like to elaborate on some of the points raised by Sheldon et al. (2021) and try to clarify the arguably complicated nature of the DS. For this, it is important to closely examine the literature that has been cited in support of the authors’ hypotheses and make a distinction between the production and perception of DS.