Revisiting the simulation of smiles model: The what, when, and why of mimicking smiles

Facial expressions accompany almost every social exchange, but there is more to them than meets the eye. Darwin believed that facial expressions are vestiges of solutions to long-past evolutionary challenges (Darwin, 1872); for instance, the lifted upper lip and wrinkled nose accompanying feelings of disgust probably evolved to help block or expel noxious smells or poisonous food. According to the Darwinian account, social animals, including our ancestors, began to use facial actions to communicate internal states and external dangers to others. Later, the communicative purpose of the facial movements eventually superseded the functional purpose (Darwin, 1872; Frith, 2009; Hess & Thibault, 2009). However, the expressions of modern-day humans may still serve those original functions. For example, when individuals made facial expressions of fear (compared to neutral emotion), they executed more efficient eye movements in the localization of targets, their visual fields were subjectively larger, and their nasal volume and air velocity during inspiration increased. All of these reactions are useful in preparation for fighting or fleeing from a threat. In contrast, facial expressions of disgust appear to be associated with the constriction and slowing of such processes (Susskind et al. 2008; cf. Krusemark & Li, 2011) so that perception and ingestion of toxic or rotten objects can be minimized. Thus, expressive facial action can aid in generating the bodily responses that promote successful resolution of challenges to survival. Still, human facial expressions are primarily communicative, and are a means to quickly convey status, motivation, affect, and other social information including the probability of cooperative or prosocial action (Anderson & Thompson, 2004; Brown, Palameta, & Moore, 2003; Scharlemann, Eckel, Kacelnik, & Wilson, 2001) and information about personality (Ames & Johar, 2009; Hareli & Hess, 2010; Harker & Keltner, 2001). Facial expressions also function as rewards (Matthews & Wells, 1999) and punishments (Blair, 1995) in learning (see also Blair, 2003; Gerull & Rappee, 2002; Mumme & Fernald, 1996). In this context there is lively debate about whether expressions of emotion are universal (Jack, Garrod, Yu, Caldara, & Schyns, 2012; Russell, 1994) and about how differences might be produced across individuals and across cultures (Elfenbein, Beaupré, Lévesque, & Hess, 2007; Wehrle, Kaiser, Schmidt, & Scherer, 2000). Whether expressions of emotion are innate or learned via socialization, it seems clear that typically developing individuals can usually accurately interpret and act on the facial expressions of others.