As a highly social species, the mutual understanding of emotions is fundamental to the functioning of all human societies. Specifically, communicating emotions – internal states that can influence cognition and behaviour – can provide reliable predictions about the environment, thereby allowing others to adjust their cognitions and behaviours for adaptive action. For example, accurately detecting anger and responding with a submissive behaviour (or a greater display of physical threat) typically avoids a harmful or potentially fatal interaction (Dukas 1998). In contrast, where communication breaks down – for example, due to difficulties expressing or understanding a facial expression – significant negative consequences can arise including social isolation or physical or mental harm (e.g., Baron-Cohen, Leslie and Frith 1985; Hawkley and Cacioppo 2007; LeMoult et al. 2009). Thus, understanding how accurate emotion communication is achieved and why it breaks down is of central importance in facilitating the smooth functioning of all human societies.

As a highly sophisticated social species (e.g., Wilson 2012), humans can communicate a wide range of nuanced emotions, achieved primarily using the face (but see also voice and body posture, e.g., Belin et al. 2008; de Gelder 2009; Sauter et al. 2010) – a powerful communication tool that is equipped with numerous independent muscles that can be combined at different intensities over time (e.g., Drake, Vogl and Mitchell 2010). Consequently, the human face is capable of generating a broad spectrum of complex dynamic patterns, facial expressions, to support emotion communication. Understanding facial expressions of emotion – the origins and evolution, meaning and function – has long been a source of fascination and debate in fields such as psychology, anthropology and philosophy. One of the most infamous debates has focused on the universality of facial expressions of emotion – that is, on whether facial expressions of the six basic emotions (happiness, surprise, fear, disgust, anger and sadness) are expressed and recognized in the same way across cultures.