Communication is a defining feature of sociality, and faces offer others a wealth of information about identity, emotion and intention. Despite this, we know little about what makes facial communication complex, and how to distinguish between species that have sophisticated facial communication, and those that do not. Traditional approaches rely on simplistic methods such as counting the number of facial expressions produced, or the number of facial muscles. However, these methods do not capture the richness of truly complex facial communication, such as dynamic movements, blended and graded facial expressions. Without better techniques to assess complexity in a more meaningful and accurate way, our understanding of the evolution of communication is inhibited.
In this project, we will combine the Facial Action Coding System (an anatomically-based system designed to break-down facial expressions into their most basic observable units, the contraction of individual facial muscles) with Social Network Analysis (a method to measure relationships between units in a system) to develop a novel framework to study communication via the face: NetFACS. In this framework, facial expressions will be conceptualised as a network of facial muscles, interacting to produce communication. This method will take into account the dynamic nature of facial expressions and therefore, better reflect its complexity.
Once developed, we will use NetFACS to test the current leading hypothesis that social complexity drives the evolution of facial communication complexity. The idea is that individuals living in large groups, with individualised relationships and numerous social roles, need to negotiate multifaceted social interactions; strategically assess and respond to group members quickly and accurately to form and maintain relationships. Complex social communication could provide one solution to these problems. Macaques are the perfect model to test this hypothesis as all species share similar demographic characteristics (e.g. multi-male, multi-female groups of similar sizes) but differ in degree of social tolerance (i.e. egalitarian vs despotic) – the ability of individuals to interact with a large number of individuals in many different ways – which is a key aspect of social complexity. We expect more tolerant species to have more complex facial communication.
Ultimately, this project will provide a tool to quantify the complexity of facial expressions and invigorate a new way of thinking about communication complexity across species.
We want to radically change how facial expressions are defined and studied. We will rethink facial expression as being a fluid network of interacting muscles producing communication, instead of static emotionally grounded configurations of the whole face. Our project will lead to the creation of a freely available tool, NetFACS, which will allow scientists to tackle new and important questions about the evolution of complex communication, across species and disciplines. As an evaluation of our methodology, we will test the leading hypothesis that group living drives the evolution of complex facial communication.