Sensorimotor contributions to emotion perception
When people perceive and process the meaning of others' facial expressions, it often activates brain systems responsible for expression production. This sensorimotor simulation contributes to the understanding of the other person's facial expression.
Social functions of smiles and laughter
According to our social functional perspective, smiles and laughter can take different forms to accomplish different social tasks. Smiles and laughter can be rewards to the self and others, affiliation cues that convey non-threatening intentions, and signals of dominance and superiority.
Historical migration patterns shape expressivity
Over the last 500 years, some regions in the world experienced waves of immigration from a variety of source countries, while the populations of other regions have remained relatively stable. This cultural difference, known as historical heterogeneity, explains cultural variability in nonverbal expression.
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.
Human survival depends on our ability to coordinate our behavior with the people around us. This can already be a challenging task when we share a language, social scripts, traditions, and norms. Establishing trust and mutual understanding with other people becomes even more challenging when you don't share a culture and language. This is a situation people often find themselves in when they immigrate to a new land. Some present-day cultures, like the U.S. and Brazil, are built on hundreds of years of immigration from a variety of source countries. Our lab studies a particular cultural solution for communicating and establishing trust with people in historically diverse cultures.
We propose that settlers in historically heterogeneous lands established communication and trust by developing a culture of greater emotional transparency. People are perceived as more trustworthy and are easier to understand when they produce bigger, clearer nonverbal expressions, and greater expressivity could compensate for the lack of shared language, norms, and institutions in heterogeneous cultures. Once a culture of greater emotional transparency is established, it can persist over generations, even as the new culture converges on a common language and norms. We study the emotion expression consequences of historical heterogeneity, which can be quantified as the number of source countries that contributed to a present-day nation's population over the course of 500 years.
Below we describe evidence that the historical heterogeneity scores of countries (see map) explains between-cultural variability in present-day expressivity. See our recent Current Opinion in Psychology piece for more details.
People from heterogeneous cultures are more emotionally expressive
We used heterogeneity scores to predict the self-reported emotional display rules of participants from 32 countries. We found that people from more historically heterogeneous cultures thought it was more appropriate to express feelings openly, compared to people from more homogeneous cultures. A massive behavioral study (N=866,726) from a separate lab supports our initial finding, showing that heterogeneity scores predict how much people smile while watching videos in front of a webcam.
They produce more cross-culturally recognizable facial expressions
In another paper we re-analyzed data on cross-cultural emotion recognition accuracy from 92 articles using participants from 82 separate cultures. We used the historical heterogeneity scores of both the expressers' cultures and the perceivers' cultures to predict accuracy and found that the more heterogeneous the expresser's culture, the greater the cross-cultural emotion recognition accuracy. This effect persisted even when we included in our model another important cultural dimension, individualism-collectivism. We suggest that heterogeneous cultures experienced increased pressure to use clear facial signals that are more universally recognizable, creating between-culture variability in expression recognizability.
And they emphasize different reasons for smiling
We study 3 specific tasks we consider fundamental to social living: rewarding the behavior of others, affiliating and maintaining bonds, and exerting dominance for the purposes of status negotiation (see Social Functions section for details). According to our social functional account, smiles and laughter are particularly well-suited for solving all 3 tasks. While we propose that all people across cultures must solve these 3 tasks, different cultural contexts may make particular tasks more or less relevant to daily life. In homogeneous cultures, which historically experienced greater population stability, cultural norms and hierarchical relationships are typically clearer than in heterogeneous cultures. We therefore predicted that people in homogeneous cultures would consider status negotiation (dominance) to be a better reason for smiling than people in more heterogeneous cultures. Because people in heterogeneous cultures historically experienced increased pressure to reduce uncertainty and establish trust with others, we predicted people in heterogeneous cultures would endorse reasons for smiling related to friendliness and affiliation more than people in homogeneous cultures. We found support for these predictions when we asked participants from 9 countries to rate the extent to which 15 different emotional/motivational states cause people to smile in their culture. Participants clustered into two groups based on their responses, with significantly more participants from homogeneous cultures in the cluster that emphasized hierarchy-related reasons for smiling more and affiliation-related reasons less.