Facial expressions convey essential information about the expresser's intentions and attitudes towards people and things in the environment. This social information guides observers' behavior: a toddler learns to avoid a hot stove after seeing her mother's expression of fear; a teenager throws away his Power Rangers t-shirt after a classmate smirks at it; a woman walking past a man on the street feels safe after seeing his non-threatening, affiliative smile. Clearly we say a lot with our faces. Attending to, correctly interpreting, and responding appropriately to the often subtle expressions of others is one of the most important tasks we accomplish as social animals.
Our lab studies the underlying processes that support emotion perception. We propose that the ability to understand the meaning of others' facial expressions relies, in part, on the ability to produce facial expressions. In a process referred to as sensorimotor simulation, perceiving an expression activates the brain network involved in expression production, giving the perceiver access to associated cognitive and emotional states. The perceiver can infer the mental state underlying the expresser's facial expression and predict the expresser's next behaviors. Of course, this cross-modal contribution is not the only way we can understand facial expressions. People can process and recognize expressions like they would any other visual input. But we suggest that sensorimotor simulation, particularly when perceiver and expresser are situated in the same context, gives an additional boost to emotion perception. Sensorimotor simulation is sometimes reflected in measurable facial mimicry, or automatic facial muscle activity.
Below we describe recent supporting evidence from our lab. Also see our 2016 Trends in Cognitive Science review for an overview.
Disrupting facial feedback reduces emotion perception accuracy
To examine whether sensorimotor activity contributes to emotion perception, we disrupt people's facial sensorimotor systems while they complete different emotion perception tasks. In one study, participants who wore sports mouth guards were worse than control participants at distinguishing between dynamic spontaneous and posed smiles. In another study, wearing a facial feedback-distorting gel face mask reduced participants' ability to distinguish highly similar facial expressions apart. In a recent study (in prep), participants wearing medical tape on their faces were slower to categorize videos of expressions as negative or positive. We suggest that manipulating facial sensorimotor activity allows us to more directly test the causal contribution of simulation to emotion perception, compared to studies that correlate measured facial mimicry and emotion recognition accuracy.
Prolonged pacifier use affects boys' facial mimicry and emotional competence
If facial sensorimotor activity supports emotion perception, what happens when it is chronically inhibited during social interactions? Infant-caregiver interactions involve extensive facial mimicry, which in addition to building bonds may foster the development of sensorimotor simulation processes. Pacifiers prevent the baby from fully engaging in such facial expression exchanges. Studies from our lab suggest that length of pacifier use in boys negatively predicts the amount of automatic facial mimicry and emotional competence they display later in development. Adult observers also mimic babies' facial expressions less when their mouths are covered by a pacifier. Upcoming work will investigate why girls' pacifier use does not appear to predict later emotional competence. We speculate that gendered socialization, which encourages greater emotional expressivity in girls, buffers them against the effects of pacifiers.
Moderators of sensorimotor simulation and facial mimicry
Perceivers likely rely more on sensorimotor simulation when it is important for them to know what the expresser is feeling and thinking--for instance, if the expresser is a romantic partner or authority figure. In one study, men who received intranasal oxytocin, a hormone thought to be important for social bonds with ingroup members, demonstrated more facial mimicry compared to men who received a placebo. Although the precise social consequences of oxytocin are unclear, this study and others suggest facial mimicry is sensitive to social contexts.
Another study found that people mimic facial expressions more when they can achieve eye contact with the expresser. Eye contact may signal to the perceiver that the facial expression is self-relevant and therefore demands deeper processing.