one case study suggests that the ability to smile is

Cover Story

The psychological study of smiling.

A smile begins in our sensory corridors. The earcollects a whispered word. The eyes spot an old friend on the station platform. The hand feels the pressure of another hand. This emotional data funnels to the brain, exciting the left anterior temporal region in particular, then smolders to the surface of the face, where two muscles, standing at attention, are roused into action: The zygomatic major, which resides in the cheek, tugs the lips upward, and the orbicularis oculi, which encircles the eye socket, squeezes the outside corners into the shape of a crow’s foot. The entire event is short — typically lasting from two-thirds of a second to four seconds — and those who witness it often respond by mirroring the action, and smiling back.

Other muscles can simulate a smile, but only the peculiar tango of the zygomatic major and the orbicularis oculi produces a genuine expression of positive emotion. Psychologists call this the “Duchenne smile,” and most consider it the sole indicator of true enjoyment. The name is a nod to French anatomist Guillaume Duchenne, who studied emotional expression by stimulating various facial muscles with electrical currents. (The technique hurt so much, it’s been said, that Duchenne performed some of his tests on the severed heads of executed criminals.) In his 1862 book Mecanisme de la Physionomie Humaine, Duchenne wrote that the zygomatic major can be willed into action, but that only the “sweet emotions of the soul” force the orbicularis oculi to contract. “Its inertia, in smiling,” Duchenne wrote, “unmasks a false friend.”

Psychological scientists no longer study beheaded rogues — just graduate students, mainly — but they have advanced our understanding of smiles since Duchenne’s discoveries. We now know that genuine smiles may indeed reflect a “sweet soul.” The intensity of a true grin can predict marital happiness, personal well-being, and even longevity. We know that some smiles — Duchenne’s false friends — do not reflect enjoyment at all, but rather a wide range of emotions, including embarrassment, deceit, and grief. We know that variables (age, gender, culture, and social setting, among them) influence the frequency and character of a grin, and what purpose smiles play in the broader scheme of existence. In short, scientists have learned that one of humanity’s simplest expressions is beautifully complex.

A True ‘Sign of Enjoyment’

Duchenne’s observations took some time to catch on with behavioral scientists. In 1924, Carney Landis, then a psychology student at the University of Minnesota, published a classic — and by today’s standards, ethically dubious — study of human facial expressions. Landis took pictures of study participants engaged in a series of activities that ranged from sacred to profane: listening to jazz music, reading the Bible, looking at pornography, and decapitating live rats. He evaluated the photographed reactions but found no evidence that certain expressions characterized certain emotions. As for smiles, Landis failed to connect them with satisfaction; in fact, smiling occurred so ubiquitously that Landis considered it an evergreen response — ”typical of any situation,” he wrote in the Journal of Comparative Psychology.

For decades, many psychologists agreed that smiles reflected a vast array of emotions rather than a universal expression of happiness. This belief persisted until the 1970s, when Paul Ekman and Wallace Friesen, psychologists at the University of California at San Francisco, captured the precise muscular coordinates behind 3,000 facial expressions in their Facial Action Coding System, known as FACS. Ekman and Friesen used their system to resurrect Duchenne’s distinction, by that time forgotten, between genuine smiles of enjoyment and other types of smiles.

In subsequent research, conducted with Richard Davidson of the University of Wisconsin, Ekman and Friesen confirmed the unique link between positive emotion and the true Duchenne smile. The researchers attached electrodes to the heads of test participants and then showed them a series of short films. Two shorts, designed to produce positive emotions, displayed frolicking animals; two others, meant to evoke negative responses, came from a nurse training video depicting amputated legs and severe burns.

Using FACS, the researchers catalogued viewer reactions and found that Duchenne smiles correlated with the pleasant films. The neural data revealed that Duchenne smiles produced greater activity in the brain’s left anterior temporal region, an area with clear connections to positive affect. (They also recorded an increase in the left parietal region, typically stimulated by verbal activity.) All told, scientists were wrong to lump smiles together as a “single class of behavior,” the trio concluded in a 1990 issue of the Journal of Personality and Social Psychology. “Clearly the Duchenne smile…is a better sign of enjoyment than other kinds of smiles.”

A renewed appreciation for Duchenne and his unique sign of joy emerged. Mental health researchers soon noticed that wherever positive emotions went, Duchenne smiles followed. Patients with depression brandished more Duchenne smiles on their discharge interviews than during their admissions, and Duchenne smiling alone — not other types of grins — was found to increase over the course of psychotherapy. Even casual, untrained observers could identify Duchenne-style faces, and based on these looks alone, assigned highly positive traits to the personality behind them.

Some researchers now believe that genuine smiles are not transient sparks of emotion but rather clear windows into a person’s core disposition. University of California at Berkeley psychological scientists LeeAnne Harker and Dacher Keltner used FACS to analyze the college yearbook photos of women, then matched up the smile ratings with personality data collected during a 30-year longitudinal study. Women who displayed true, Duchenne-worthy expressions of positive emotion in their 21-year-old photo had greater levels of general well-being and marital satisfaction at age 52. “People photograph each other with casual ease and remarkable frequency, usually unaware that each snapshot may capture as much about the future as it does the passing emotions of the moment,” Harker and Keltner wrote in a 2001 issue of the Journal of Personality and Social Psychology. A related study, published in a 2009 issue of Motivation and Emotion, confirmed a correlation between low-intensity smiles in youth and divorce later in life.

In a more recent study, published this year in Psychological Science, Ernest Abel and Michael Kruger of Wayne State University extended this line of research from emotional outcomes to a biological one: longevity. Abel and Kruger rated the smiles of professional baseball players captured in a 1952 yearbook, then determined each player’s age at death (46 players were still alive at the time of the study). The researchers found that smile intensity could explain 35 percent of the variability in survival; in fact, in any given year, players with Duchenne smiles in their yearbook photo were only half as likely to die as those who had not.

A ‘Vehicle for All Ambiguities’

Landis was correct about smiles in one regard: not all of them are genuine expressions of happiness. In addition to the Duchenne smile, Ekman described seventeen other types of smiles in his 1985 book, Telling Lies. Herman Melville understood this, once calling a smile “the chosen vehicle for all ambiguities.” People smile when they’re frightened, are flirting, horrified, or mortified. An embarrassed smile reveals itself through an averted gaze, a facial touch, and a tilt of the head down and to the left.

People also smile when they’re lying, a fact not lost on Shakespeare: Hamlet marvels at how “one may smile, and smile, and be a villain.” In the late 1960s, Ekman and Friesen theorized that a trained expert could discern a lying face from an honest one. To put this idea to the test, the researchers asked a group of young nurses to watch a disturbing video then tell an interviewer that they had actually seen a pleasant one. Their facial expressions during this lie were videotaped and FACS analyzed.

Compared to smiles taped during honest interviews, the nurses gave fewer genuine, Duchenne smiles when lying, Ekman and Freisen reported in a 1988 paper in the Journal of Personality and Social Psychology, coauthored with Maureen O’Sullivan of the University of San Francisco. The deceitful grins were betrayed by either a raised upper lip, revealing a hint of disgust, or lowered lip corners, displaying a trace of sadness. Ekman’s work with lies later inspired the television show “Lie to Me,” in which investigators solve criminal cases by interpreting facial expressions.

It’s not unusual for moments of sadness, or even bereavement, to cause a smile. The world’s best-known smile is intriguing precisely because it could indicate a range of moods; Bob Dylan described Mona Lisa as having the “highway blues.” (Harvard neurobiologist Margaret Livingstone argued, in an article in Science from 2000, that La Gioconda’s smile exists in your peripheral visual field, but vanishes when you look directly at her mouth, see sidebar.)

However, it seems that smiling through tough times does a body good. Keltner and George Bonanno of Catholic University have measured the facial expressions of people who discuss a recently deceased spouse. In a 1997 issue of the Journal of Personality and Social Psychology, the researchers reported lower levels of distress in those who displayed genuine, Duchenne laughter during the discussion, compared to those who did not.

The benefits of smiling through grief appear to occur on a biological level as well. Barbara Fredrickson and Robert Levenson once observed the facial expressions made by 72 people watching a funeral scene from the tear-jerker Steel Magnolias. Not only did fifty of the participants smile at least once during the clip, the authors reported in a 1998 paper in Cognition and Emotion, but those who did recovered their baseline cardiovascular levels more quickly than others who failed to crack a grin.

A ‘Contingent Social Display’

Smiling certainly seems built into our nature. No less an authority than Darwin, whose 1872 book The Expression of the Emotions in Man and Animals is considered a foundational text of smiling research, proposed that facial expressions are universal products of human evolution rather than unique lessons of one’s culture. The zygomatic major has a long evolutionary history, says expression researcher Jeffrey Cohn of the University of Pittsburgh, and facial muscles used for smiling are found in all humans. “There’s good evidence that the motor routine involved in smiling is inborn,” says Cohn. “The hardware is there.”

No surprise, then, that newborns can dispense and interpret facial expressions with great precision. At just 10 months, for instance, an infant will offer a false smile to an approaching stranger while reserving a genuine, Duchenne smile for its mother. Decades ago, Cohn observed how 3-month-olds reacted to changes in their mother’s expression. When mothers feigned depression, infants threw up their tiny fists in distress, and after just 3 minutes of smile-free interaction they became withdrawn.

As infants mature, their tendency to smile diverges along gender lines. The ability to produce Duchenne smiles is parceled out equally between the sexes, but men say they smile less than women and both sexes think this to be the case. So do behavioral scientists, who are nearly unanimous in their belief that women smile more than men. Broadly speaking, that seems to be true. But the differences in smiling behavior between men and women hinge on several key factors. A few years ago, a research team led by Yale psychologist Marianne LaFrance performed a massive meta-analysis of smiling research analyzing data from 162 studies and more than 100,000 participants in all, and isolated three variables that influence sex-smiling disparities.

One moderator is gender norms: When people know they’re being watched, triggering this norm, sex differences in smiling are greater than when people believe they’re alone. A second is situational constraint: When men and women share a task or role that follows rigid social rules — like those requiring flight attendants to smile and funeral directors to remain somber — the grin gap diminishes. A third moderator is emotional climate: Embarrassing or socially tense situations cause females to smile more than males, but happy or sad situations have no such effect. Smiling, LaFrance and her collaborators concluded in a 2003 issue of Psychological Bulletin, “is a highly contingent social display.”

“If you ask people who smiles more, everyone will say, ‘Women, of course,’” says LaFrance, whose book on smiling research, Lip Service, is scheduled for publication by W.W. Norton next summer. “What people don’t consider as much — both within the field of psychology and outside of it, is how variable smiling is as a function of the context of a social situation.”

Part of this variability is the cultural background of the beholder. A study published in a 2007 issue of the Journal of Experimental Social Psychology highlights the different ways that Americans and Japanese perceive smiles. When viewing emoticons, Americans located expression at the mouth, seeing 🙂 as happy and 🙁 as sad, while Japanese found it in the eyes, seeing ^_^ as joyful and ;_; as tearful. The variation may reflect an American tendency to express emotions and a Japanese tendency to suppress them; after all, as Duchenne knew, the mouth can be manipulated into a smile more easily than the eyes (see photographs on facing page). A supporting study, published earlier this year, found that Japanese participants emphasized the upper half of a face when determining its trustworthiness, whereas Americans focused on the lower half.

The presence of those around us can influence our smiles as well. An experiment led by Robert Kraut, published in a 1979 issue of Journal of Personality and Social Psychology, reported that bowlers smiled more often when facing their friends in the pit than when facing the pins on the lane. Of course people do smile to themselves, but many believe that social context pulls more strongly at our lips than pure, isolated emotion. Alan Fridlund of University of California, Santa Barbara, has found that people smile more when they imagine others around them than when they’re alone — even when their overall levels of happiness remain the same.

Signifying Altruism and Attraction

It stands to reason that if social settings influence our smiles, then smiles probably serve a social purpose. One such function, recent evidence suggests, may be to indicate altruism. To test this notion, a team of researchers led by British behavioral scientist Marc Mehu observed the smiles of test participants told to share some of the fee they received from the study with a friend. When people were engaged in this sharing activity they exhibited more Duchenne smiles than during a neutral scenario. Perhaps people issue genuine grins as a way to “reliably advertise altruistic intentions,” Mehu and his collaborators concluded in a 2007 issue of Evolution and Human Behavior.

That Duchenne smiles would announce a cooperative nature makes sense. After all, one’s level of commitment has obvious social value, and genuine smiles are difficult to feign. The ability to identify a truly group-minded person would be particularly useful to those prone to social exclusion. With this in mind, a group of researchers from Miami University of Ohio recently asked test participants to rate various smiles as genuine or fake. Before the task, some were primed for exclusion through an essay task that required them to write about a time they were rejected. Compared with a control group and others primed for inclusion, the excluded participants showed an enhanced ability to distinguish Duchenne smiles from false ones, the authors reported in Psychological Science in 2008.

Not only do people deduce useful information from smiles, they also use this knowledge to direct their own behavior. In a follow-up experiment, published in 2010 in the Journal of Experimental Social Psychology, the same researchers found that people primed for exclusion showed a greater preference to work with individuals displaying genuine Duchenne smiles than those bearing cheap grins. “Duchenne smiles are a signal of cooperation, altruisim,” says Michael Bernstein, now at Penn State Abington, lead author of both papers. “Non-Duchenne smiling isn’t necessarily bad — it doesn’t mean you’re nefarious — but it’s not a great signal. [Socially rejected people] should be looking for the best signal, and Duchenne smiles offer a better one.”

Another function of smiling (and one that anecdotal evidence supports) is that it enhances our attractiveness. One of the most famous characters in American letters, F. Scott Fitzgerald’s Jay Gatsby, had an irresistible smile that “assured you that it had precisely the impression of you that, at your best, you hoped to convey.” For its part, science has identified part of the reason for a great smile’s allure. A recent fMRI study found that viewing attractive faces activated the brain’s orbitofrontal cortex, a region involved in processing sensory rewards. While this held true for all pretty mugs, the activity in this region was even stronger when the face in focus wore a smile. “The presence of a smile may provide an important signal that a reward is or is not attainable,” the researchers wrote in a Neuropsychologia (2003). Although some might argue that the brain, in seeing a smile, has already considered the reward attained.

Abel E. and Kruger M. (2010) Smile Intensity in Photographs Predicts Longevity, Psychological Science, 21, 542–544. Bernstein M.J., Young, S.G., Brown C.M., Sacco D.F., and Claypool, H.M. (1998) Adaptive Responses to Social Exclusion Social Rejection Improves Detection of Real and Fake Smiles, Psychological Science, 19, 10, 981–983. Bernstein M.J., Sacco D.F., Brown, C.M. Young, S.G. and Claypool, H.M. (2010) A pre ference for genuine smiles following social exclusion. Journal of Experimental Social Psychology, 46, 196–199. Cohn, J.F., and Tronick E.Z. (1983) Three-Month-Old Infants’ Reaction to Simulated Maternal Depression, Child Development, 54, 185–193. Darwin, C. (1872) The Expression of the Emotions in Man and Animals, London: J. Murray. Duchenne G.B., (1990) The mechanism of human facial expression, trans. R.A. Cuthbertson, Cambridge University Press. Ekman, P. (1985) Telling Lies: Clues to deceit in the marketplace, politics, and marriage, Norton: New York. Ekman, P., Davidson, R.J., Friesen, W.V. (1990) The Duchenne Smile: Emotional Expression and Brain Physiology II, Journal of Personality and Social Psychology, 58, 342–353. Ekman, P. Wallace V. Freisen, O’Sullivan M. (1988) Smiles when lying, Journal of Personality and Social Psychology, 54, 414–420. Fredrickson, B.L., and Levenson, R.W. (1998) Positive emotions speed recovery from the cardiovascular sequelae of negative emotions, Cognition and Emotion, 12, 191–220. Fridlund, A.J., Sabini J.P., Hedlund, L.E. Schaut, J.A., Shenker, J.I., and Knauer, M.J. (1990) Audience effects on solitary faces during imagery: Displaying people in your head, Journal of Nonverbal Behavior, 14, 113–137. Harker L and Keltner D, (2001) Expressions of Positive Emotion in Women’s College Yearbook Pictures and Their Relationship to Personality and Life Outcomes Across Adulthood. Journal of Personality and Social Psychology, 80, 112–124. Hertenstein, M.J., Hansel, C.A., Butts A.M., Hile S.N. (2009) Smile intensity in photographs predicts divorce later in life. Motivation and Emotion. 33, 2, 99–105. Keltner D., and Bonanno, G (1997) A Study of Laughter and Dissociation: Distinct Correlates of Laughter and Smiling During Bereavement, Journal of Personality and Social Psychology, 73, 687–702. Kraut, R.E., Johnston R.E. (1979) Social and Emotional Messages of Smiling: An Ethological Approach, Journal of Personality and Social Psychology, 37, 9, 1539–1553. LaFrance M., Hecht, M.A., Paluck, E.L. (2003) The Contingent Smile: A Meta-Analysis of Sex Differences in Smiling, Psychological Bulletin, 129, 305–334. Landis, C. (1924) Studies of Emotional Reactions II. General Behavior and Facial Expression, Journal of Comparative Psychology, 4, 5. Livingstone, M.S. (2000) Is it warm? Is it real? Or just low spatial frequency? Science, 290, 1299. Mehua, M., Grammerb K., and Dunbara, R.I.M., (2007) Smiles when sharing, Evolution and Human Behavior, 28, 415–422. O’Doherty, J., Winston, J., Critchley, H. Perrett, D., Burt, D.M., and Dolan R.J., (2003) Beauty in a smile: the role of medial orbitofrontal cortex in facial attractiveness. Neuropsychologia, 41, 147–155. Ozono H., et al. (2010) What’s in a Smile? Cultural Differences in the Effects of Smiling on Judgments of Trustworthiness, Letters on Evolutionary Behavioral Science, 1, 15–18. Yuki, M., Maddux, W.W., Masuda, T. (2007) Are the windows to the soul the same in the East and West? Cultural differences in using the eyes and mouth as cues to recognize emotions in Japan and the United States, Journal of Experimental Social Psychology, 43, 303–311.

This article inspired me to the point of exaggeration. Being a storyteller and imaginative artist, I’ve found your insight almost to the limits of my imagination. This is where I prefer to reside. Thank you for the insight and the inspiration in a new address to whom ever might enjoy the smile.

Having just stumbled across this article, I appreciate its consideration of so many elements, such as gender, culture, social situation, and history. It also offers support for some the more recent (2012-2014) research on confidence and the body’s ability to raise levels of confidence through expansive positions. (Harvard, Cuddy) I like the idea that our smiles indicate so much about the environment and situation we are in, and are so very “readable” by others! The intuition a viewer has that a smile is genuine/Duchenne vs. forced is fascinating.

Riches and wealth doesn’t create smiles.

Measuring the hard science of smiles may help America learn the value of retaining smiles, and to be alarmed when america loses its smile.

Studying how children lose their smiles is among the most important science any nation can do to measure its well being.

@Pat – I would love more information about the study of how children loose their smile. Please share! 😀

i loved this inspirations of smile. i really change my behaviors because of this. thanks to you all contributors of this inspiration. i have a big hope to my family throughout this inspiration. i am Extremely happy.

I found this article very interesting and also very informative, with its research carried out by very reliable sources.I am currently researching for a project on well-being and this will be invaluable to me.

Well, now I know how to tell if my friend isn’t actually happy about something.

We fail to realize that nearly every smile is misunderstood by the observer because so little is accurately understood about the experiences that contributed to the development of that exact response and other’s response during learning (or training.)

Life is never so simple.

Additionally, a young human’s feedback conditioned response is largely conditioned by their satisfaction with the observer’s response and this is colored by the validity of everyone’s interpretations of the other’s behaviour.

so … is it only wen a person is happy he/she smiles? I’ve seen people smiling even in extreme pain…. so whats it about

thank you for the very informative article. It gives a whole range of situations where smile comes into effect. You made me smile. Hayim

Smile More Worry Less

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How and why could smiling influence physical health? A conceptual review

Affiliations.

• 1 Department of Biobehavioral Health, Pennsylvania State University, University Park, PA, USA.
• 2 Department of Psychological Science, University of California, Irvine, CA, USA.
• 3 Department of Psychology, University of Kentucky, Lexington, KY, USA.
• PMID: 35285408
• DOI: 10.1080/17437199.2022.2052740

ABSTRACT Smiling has been a topic of interest to psychologists for decades, with a myriad of studies tying this behavior to well-being. Despite this, we know surprisingly little about the nature of the connections between smiling and physical health. We review the literature connecting both naturally occurring smiles and experimentally manipulated smiles to physical health and health-relevant outcomes. This work is discussed in the context of existing affect and health-relevant theoretical models that help explain the connection between smiling and physical health including the facial feedback hypothesis, the undoing hypothesis, the generalized unsafety theory of stress, and polyvagal theory. We also describe a number of plausible pathways, some new and relatively untested, through which smiling may influence physical health such as trait or state positive affect, social relationships, stress buffering, and the oculocardiac reflex. Finally, we provide a discussion of possible future directions, including the importance of cultural variation and replication. Although this field is still in its infancy, the findings from both naturally occurring smile studies and experimentally manipulated smile studies consistently suggest that smiling may have a number of health-relevant benefits including beneficially impacting our physiology during acute stress, improved stress recovery, and reduced illness over time.

Keywords: Smiling; facial expressions; physical health; positive affect; positive emotion; stress.

Publication types

• Facial Expression*
• Interpersonal Relations
• Smiling* / physiology

Facial Mimicry and Social Context Affect Smile Interpretation

• Original Paper
• Open access
• Published: 10 August 2023
• Volume 47 , pages 471–488, ( 2023 )

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You have full access to this open access article

• Anna Orlowska 1 ,
• Magdalena Rychlowska 2 ,
• Piotr Szarota 1 &
• Eva G. Krumhuber 3  

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Theoretical accounts and extant research suggest that people use various sources of information, including sensorimotor simulation and social context, while judging emotional displays. However, the evidence on how those factors can interplay is limited. The present research tested whether social context information has a greater impact on perceivers’ smile judgments when mimicry is experimentally restricted. In Study 1, participants watched images of affiliative smiles presented with verbal descriptions of situations associated with happiness or politeness. Half the participants could freely move their faces while rating the extent to which the smiles communicated affiliation, whereas for the other half mimicry was restricted via a pen-in-mouth procedure. As predicted, smiles were perceived as more affiliative when the social context was polite than when it was happy. Importantly, the effect of context information was significantly larger among participants who could not freely mimic the facial expressions. In Study 2 we replicated this finding using a different set of stimuli, manipulating context in a within-subjects design, and controlling for empathy and mood. Together, the findings demonstrate that mimicry importantly modulates the impact of social context information on smile perception.

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Introduction

The ability to understand other people’s emotions and to judge their facial expressions is essential for social interaction (Kappas et al., 2013 ). Although prototypical emotion expressions can be easily recognized using simple pattern matching, nuanced displays are more difficult to discern due to their subtlety and complexity (Hess et al., 1997 ). Distinguishing between different types of smiles is an example of such a complex recognition task. Even though as many as 18 types of smiles have been described in the literature (Ekman, 2009 ), the most commonly used smile typology is the distinction between enjoyment (genuine, Duchenne) and non-enjoyment (posed, non-Duchenne) smiles. Accordingly, smiles that involve a contraction of both the zygomaticus major muscle (Action Unit (AU) 12; Facial Action Coding System (FACS), Ekman et al., 2002 ) and orbicularis oculi muscle (AU 6) tend to be classified as genuine, whereas non-enjoyment smiles lack activation of the orbicularis oculi. Besides this distinction, smiles can be categorized based on their social function (e.g., Ambadar et al., 2009 ; Niedenthal et al., 2010 ). For example, Niedenthal and colleagues ( 2010 ) proposed a classification of smiles related to three main areas of social interaction: reward smiles, which communicate positive affective states; affiliation smiles, which communicate prosocial motives; and dominance smiles, associated with negotiating and maintaining one’s social status. Recent studies reveal that these three smile types are morphologically different (Rychlowska et al., 2017 ), and that people are able to identify and distinguish them (Orlowska et al., 2018 ).

Despite perceptual differences between different smile types, accurately judging smiles may still be challenging as these expressions may involve complex facial movements (Krumhuber & Kappas, 2005 ; Krumhuber & Manstead, 2009 ) and facial actions co-occurring with the contraction of the zygomaticus major muscle (Rychlowska et al., 2017 ). In addition, the multitude of messages that smiles convey suggests that their interpretation is influenced by the affective state of the perceiver or characteristics of the situation. In other words, although the analysis of the morphology of smiles is necessary to judge these facial expressions, it may not be sufficient for an accurate interpretation of their meaning (Hess & Fischer, 2013 ; Niedenthal et al., 2010 ). Instead inferences may be guided by other mechanisms, including sensorimotor simulation (Niedenthal et al., 2010 ; Wood et al., 2016 ) and contextual influences (e.g., Hess and Hareli, 2015 ).

The term “sensorimotor simulation” describes an active representation of the other person’s state, generated in the motor, somatosensory, and reward brain circuits (Ferrari & Coudé, 2018 ; Pitcher et al., 2008 ). This complex process is often indexed by facial mimicry (Wood et al., 2016a , b ) a phenomenon defined as a spontaneous, unconscious imitation of others facial expressions (Dimberg & Thunberg, 1998 ). Interestingly, the empirical evidence on the role of mimicry in emotion processing has been mixed so far. Moreover, the effects of mimicry can be confused with the effects of other constructs such as empathy (Kosonogov et al., 2015 ) or mood (Forgas & East, 2008 ; Niedenthal et al., 2001 ). Specifically, highly empathetic observers can be more accurate in recognizing facial expressions, and being in a happy emotional state can increase a person’s sensitivity to subtle changes in smiles (Niedenthal et al., 2001 ). Although several studies suggest that disrupting facial movements decreases observers’ ability to judge emotion expressions (e.g., Maringer et al., 2011 ; Oberman et al., 2007 ; Ponari et al., 2012 ), others do not show associations between the magnitude of facial mimicry and the accuracy of emotion recognition (e.g., Blairy et al., 1999 ; Korb et al., 2014 ; Orlowska et al., 2018 ). One potential explanation for such discrepancies is that mimicry and sensorimotor processes act as a guide for complex facial processing tasks; for example, when observers judge non-prototypical facial expressions (Hess & Fischer, 2013 ; Niedenthal et al., 2010 ; Wood et al., 2016b ). Interpreting subtle variations between different smile types is an example of such a task, which is likely to be informed by the perceiver’s facial mimicry. In line with this notion, studies show that when people are unable to freely move their facial muscles, the ability to infer other’s emotions, in particular expression authenticity, is impaired (Maringer et al., 2011 ; Oberman et al., 2007 ; Ponari et al., 2012 ; Rychlowska et al., 2014 ).

Beyond sensorimotor processes, another important factor in smile interpretation is the observer’s belief about what the smile means in a particular situation (Fischer & Hess, 2017 ; Greenaway et al., 2018 ; Hess & Hareli, 2015 ). Facial expressions do not appear in isolation but are embedded within a given context (Barrett et al., 2011 ). As a result, the interpretation of facial expressions is often guided by extraneous factors such as body posture (e.g., Aviezer et al., 2008 ), the presence of other people (e.g., Gray et al., 2017 ), group status or cultural background of the expresser (e.g., Crivelli et al., 2017 ). One particularly important source of such influences is the presence of verbal information about the meaning of facial expressions (Barrett et al., 2007 ). Psychophysiological research suggests that learned categories and prior knowledge guide the extraction of information from visual objects such as faces (Sowden & Schyns, 2006 ). Consistently, facial expressions are easier to recognize when observers are provided with labels that reduce ambiguity and boost categorical perception (Barrett et al., 2007 ; Fugate et al., 2010 ; Nook et al., 2015 ). When emotionally ambiguous faces (e.g., blends of anger and sadness) are labelled as “angry”, they are further remembered as angrier than the same faces labelled as “sad” (Halberstadt & Niedenthal, 2001 ). A study by Krumhuber and colleagues ( 2021 ) found that such effects extended to posed smiles, which observers misremembered as genuine smiles after seeing them paired with a happy context scenario. Another study by the same team (Namba et al., 2020 ) showed that verbal descriptions affected perceivers’ judgments of posed smiles, such that these smiles appeared more genuine when paired with descriptions of happy situations than when paired with descriptions of situations implying politeness. Facial expression processing can also be impaired by providing verbal information that is incongruent with the visual percept (Goodenough & Tinker, 1931 ; Knudsen & Muzekari, 1983 ; Woll & Martinez, 1982 ). Beyond simply labelling facial expressions, verbal information can refer to events and situations that observers associate with specific feeling states based on their experiential knowledge (Barsalou, 2008 ).

Importantly, the influences of sensorimotor simulation and contextual information on the processing of facial expressions may interact with each other. According to the Accessibility Model of Emotion Self-Reports (Robinson & Clore, 2002 ), people are more likely to interpret feelings using generalized beliefs and stereotypes when the direct emotion experience is not accessible. Applying this reasoning to facial expression processing, when judging emotion displays such as smiles, observers may use two sources of information: their direct bodily experience resulting from seeing and simulating the expression; and their conceptual knowledge about what this expression means in a given context. However, alterations of facial mimicry, the resulting disruption of sensorimotor simulation, and the reduced emotion experience may increase observers’ reliance on their conceptual knowledge about the meaning of a given facial expression. Research on emotion expression in groups indirectly supports this prediction. As such, people tend to mimic facial displays of their in-group members to a greater extent than facial displays of members of other groups (Bourgeois & Hess, 2008 ; Hess et al., 2022 ). Conversely, observers’ interpretation of facial expressions of out-group members is influenced by stereotypic beliefs about the target group (Hess & Kirouac, 2000 ).

Surprisingly, there exists only one empirical study to date that provides a direct test of the joint influences of facial mimicry and social context on the interpretation of facial expressions. By asking participants to hold a pencil in their mouth, Maringer et al. ( 2011 , Study 2) showed that restricting mimicry increased their reliance on contextual information about the meaning of genuine smiles. Specifically, participants presented with positive contextual information rated smiles as more genuine than those given ambiguous information. Although this research provides an interesting initial demonstration of how both facial mimicry and observers’ semantic knowledge about the context contribute to smile interpretation, several limitations should be noted. First, the results are based on very small sample sizes (12 participants per condition), thereby risking type 1 error, an issue particularly pertinent given recent failures of reproducibility in the facial feedback literature (Coles et al., 2019 ; Wagenmakers et al., 2016 ). Second, the study used computer-generated faces as stimuli, which raises objections regarding the ecological validity and generalization of the findings to real human expressions (Kätsyri et al., 2019 ).

The Present Research

The aim of the present research is to test the joint effects of mimicry restriction and verbal context information on the interpretation of smiles. For this purpose, we conducted two highly powered studies employing photographs of smiling people as stimuli. Given that posed smiles convey more ambiguous messages and are harder to classify than genuine enjoyment smiles (Johnston et al., 2010 ; Orlowska et al., 2018 ; Rychlowska et al., 2017 ), the study’s focus was on non-enjoyment smiles derived from two different databases.

In Study 1, participants watched images of non-enjoyment smiles presented either in a happy context, in which genuine expressions would be expected, or in a polite context in which posed expressions would be expected (between-subjects). For half the participants, facial mimicry was restricted and the remaining participants could freely move their faces. We predicted that, among participants whose mimicry was restricted, judgments of the extent to which the smiles were affiliative (versus happy) would be strongly influenced by the context. Such influence should be weaker for participants who could mimic the observed smiles.

Study 2 used a different set of real enjoyment and non-enjoyment smiles, and manipulated social context as a within-subjects variable. In addition to participants’ judgments of the smile meaning, we examined the extent to which participants were able to correctly remember the smiles that they had previously seen. Using these two dependent measures allowed us to examine the extent to which the effects of context and mimicry restriction vary with task demands (Barrett et al., 2007 ). In light of previous research showing that facial mimicry interacts with empathy (Jospe et al., 2018 ; Kosonogov et al., 2015 ; Hsu et al., 2018 ), and affects the perception of facial expression in a way similar to mood (Niedenthal et al., 2001 ), we further included empathy and mood as control variables. Similar to Study 1, we predicted that smile judgments would be more strongly influenced by social context when mimicry is inhibited than free.

Participants and Design

A total of 176 participants were recruited face to face at the university campus or via the departmental subject pool. Responses from three participants who correctly guessed the purpose of the study were excluded from analysis, leaving a final sample of 173 participants (59 male, M age = 21.20 years, SD  = 4.76). All participants identified themselves as White. Sensitivity analysis using G*Power 3.1 (Faul, Erdfelder, Lang, & Buchner, 2007 ) indicated that this sample size was sufficient to detect a medium-sized interaction effect ( f  = 0.25) with 90% statistical power (α = 0.05).

The study manipulated facial mimicry (free vs. restricted) and the context in which smiles were displayed (polite vs. happy) in a between-subjects experimental design. Participants were randomly assigned to one of the four conditions, resulting in approximately 43 persons per group. Ethical approval was granted by the departmental ethics committee. Subjects provided written informed consent prior to participation.

The facial stimuli consisted of full colour, frontal images (size: 960 × 540 pixels) of eight (four female) White adult faces with direct gaze and neutral background. Images were retrieved from a stimulus set developed by Martin and colleagues (Martin et al., 2018 ) and displayed a non-enjoyment smile corresponding to the description of affiliation smiles (Rychlowska et al., 2017 ). In morphological terms (FACS, Ekman et al., 2002 ), the smile expressions involved the Lip Corner Puller (Action Unit (AU) 12) and Chin Raiser (AU17), with or without the Brow Raiser (AU1 + 2).

We conducted a pilot study to select the verbal context labels for the main experiment. For this, a separate group of participants ( N  = 33; 27 women) rated the likely occurrence of a reward, affiliation, and dominance smile (Niedenthal et al., 2010 ; Rychlowska et al., 2017 ) in 15 different situations related to the job market. In order to choose situations most conducive to enjoyment (reward) and non-enjoyment (affiliation) smiles, we opted for two verbal descriptions that participants most frequently associated with affiliation smiles (“smiling during a job interview”, 97%) and reward smiles (“smiling after receiving a dream job offer”, 91%).

Participants were tested individually on computers running Qualtrics, a web-based software (Provo, UT). Upon arrival, they were informed that the study aimed to develop training materials for improving job interview skills and that their task was to rate smiles, as making appropriate facial expressions can contribute to one’s success at a job interview. Participants were then randomly assigned to one of the four experimental conditions. Half the participants learned that people’s judgments of others’ faces are more objective if their own facial movement is restrained. Hence, they would hold a pencil in their mouth while performing the smile evaluation task. The experimenter explained that the pencil should be held sideways, using lips and teeth, without exerting any pressure, and they then demonstrated the correct way of holding it. This version of the pen-in-mouth procedure was identical to techniques previously used to examine the effects of restricting mimicry on judgments of facial expressions (Maringer et al., 2011 ; Niedenthal et al., 2001 ). Single-use disinfection wipes were provided to clean the pencil before using it. The other half of participants, who were assigned to the free mimicry condition, did not receive such instructions and were able to freely mimic the smile expressions.

For the manipulation of social context, half the participants were informed that the images they would see featured people who were “smiling during a job interview” (polite condition). The other half was told that the persons were “smiling after receiving a job offer” (happy condition). Prior to the smile evaluation task, we tested the validity of the two scenarios, examining whether the polite context would be more conducive to non-enjoyment affiliation smiles than the happy context, which in turn should encourage enjoyment reward smiles. To that end, subjects were asked to imagine a person smiling “during a job interview” or “after receiving a job offer”, consistent with the condition to which they were assigned. They then rated the extent to which the imagined smile would communicate that the person wanted “to be nice and to express positive intentions” (affiliation rating) or was “feeling happy and content” (happiness rating), using scales ranging from 0 to 100%. Participants’ ratings of these two dimensions were non-independent and had to add up to 100%.

The main smile evaluation task involved the presentation of eight smile expressions in combination with one of the two social context scenarios (happy or polite). The context information was shown at the top of the screen together with each stimulus. Presentation order was randomized, with each smile being displayed for 3 s. For each face-context pair, participants rated the extent to which the smile would communicate that the person wanted “to be nice and to express positive intentions” (ratings of affiliation, from 0 to 100%) or was “feeling happy and content” (ratings of happiness, from 0 to 100%). Again, both ratings were complementary and added up to 100%. At the end of the procedure, participants were probed for suspicion, thanked and debriefed.

Manipulation Check

To examine participants’ a priori beliefs about the type of smile expected in the two social context scenarios, we conducted a 2 (context: polite, happy) by 2 (mimicry: free, restricted) between-subjects ANOVA on ratings of affiliation (averaged across the stimulus faces) as the dependent variable. Consistent with predictions, participants expected smiles paired with the polite context to communicate more affiliation ( M  = 73.55, SD  = 16.81), and thus less happiness than smiles paired with the happy context ( M  = 29.08, SD  = 24.31), F (1, 169) = 194.31, p  < .001, η p ² = 0.53. In other words, the polite context was more conducive to the non-enjoyment affiliation smiles than the happy context. Participants in the free mimicry condition expected smiles to be less affiliative ( M  = 46.90, SD  = 30.41) than those in the muscle-restricted condition ( M  = 56.05, SD  = 30.08), but the main effect of mimicry did not reach conventional levels of significance, F (1, 169) = 4.04, p  = .05. The interaction between mimicry and context was not significant, F (1, 169) = 0.19, p  = .660, η p ² = 0.001.

Effects of Context and Mimicry on Judgments of Smiles

Ratings of affiliation were averaged across the stimulus faces and analyzed in a between-subjects ANOVA as a function of context and mimicry. The main effect of context was significant, F (1, 169) = 55.58, p  < .001, η p ² = 0.25, such that smiles were perceived as more affiliative when they were presented together with a polite ( M  = 67.42, SD  = 13.92) than with a happy context ( M  = 49.28, SD  = 18.14). Mimicry had no effect on perceived affiliation, F (1, 169) = 0.27, p  = .606, η p ² = 0.002. However, there was a significant interaction between context and mimicry, F (1, 169) = 7.60, p  < .006, η p ² = 0.04 (see Fig.  1 ). As expected, the impact of context on smile ratings was stronger when facial mimicry was restricted (polite context: M  = 71.17, SD  = 2.35; happy context: M  = 46.38, SD  = 2.52, F (1, 169) = 51.81, p  < .001, η p ² = 0.24) than free (polite context: M  = 63.22, SD  = 2.49; happy context: M  = 51.81, SD  = 2.35, F (1, 169) = 11.11, p  = .001, η p ² = 0.06).

Ratings of affiliation as a function of social context and mimicry in Study 1. Error bars represent standard errors of the mean (SEM)

In Study 1, we tested whether restricting the ability to mimic would moderate the influence of verbal context on participants’ judgments of affiliation smiles. Consistent with our predictions, participants held specific beliefs about the meaning of smiles in different situations. Specifically, they believed that the context of a job interview (polite context) is more conducive to non-enjoyment affiliation smiles than the context of receiving a job offer (happy context), which in turn was perceived as conducive to enjoyment or reward smiles. In our study, verbal information about such contexts significantly affected participants’ evaluations of smiles. Specifically, these expressions were judged as conveying more niceness and positive intentions and less happiness and contentment when they occurred in the context of a polite than happy situation. As predicted, such contextual influence was found to be stronger for participants whose mimicry was restrained, suggesting that they relied more on conceptual knowledge in order to judge the genuineness of the smile. In Study 2, we aimed to replicate the present findings and control for two potential moderating variables—empathy and mood.

The procedure for this study was similar to the one used in Study 1. Participants judged smile expressions presented in a polite and happy context under conditions of free and restricted mimicry. This time, however, we used a different set of facial stimuli. We also manipulated the social context as a within-subjects variable to account for possible individual differences. As in Study 1, participants rated the extent to which each smile communicated affiliation and happiness. Since the memory of facial expressions is also likely to be affected by both verbal information (Krumhuber et al., 2021 ; Woll & Martinez, 1982 ) and mimicry restriction (Wood et al., 2016 ), in addition to smile judgments, we assessed how accurately participants remembered the smiles they saw. Specifically, we examined whether, similarly to participants’ judgments of smiles, their memory of smiles previously seen would be more strongly influenced by context under conditions of restricted mimicry. Furthermore, we included control measures of empathy and mood to test whether the interaction of context and mimicry would persist after including these variables in the analysis. As in Study 1, we predicted that judgments of smiles would be more strongly influenced by social context when input from mimicry is inhibited rather than free.

A total of 66 participants (50 women, M age = 22.71 years, SD  = 5.35) were recruited at the university campus and completed the study without remuneration. Sixty-five participants identified themselves as White and one reported “other ethnical background” (Turkish nationality). Sensitivity analysis using G*Power indicated that this sample size was sufficient to detect a medium-sized interaction effect ( f  = 0.24) with 90% statistical power (α = 0.05, r cor = 0.3).

The study used a mixed experimental design, with facial mimicry (free vs. restricted) as a between-subjects variable and context information (polite vs. happy) as a within-subjects variable. Participants were randomly assigned to one of the two mimicry conditions (free: 34 participants, restricted: 32 participants). Ethical approval was granted by the departmental ethics committee, and subjects provided written informed consent prior to participation.

The facial stimuli consisted of full colour, frontal images of 12 White female faces displaying a posed smile and a genuine smile for a total of 24 photographs. All models were presented with direct gaze and on a neutral background. Images were retrieved from stimuli sets developed by Johnston et al. ( 2010 ) and McLellan et al. ( 2010 ). All smiles involved the Lip Corner Puller (AU12). Genuine smiles corresponded to the description of a Duchenne smile (Frank et al., 1993 ) in that they involved both the Lip Corner Puller (AU12) and Cheek Raiser (AU6). In contrast, posed smiles did not involve AU6.

To measure participants’ empathy levels, we used the Empathy Quotient questionnaire (Eq. 40, Baron-Cohen and Wheelwright, 2004 ), which consists of 40 items presented as statements such as “I find it easy to put myself in somebody else’s shoes” or “I am good at predicting how someone will feel.” Participants have to use a 4-point Likert scale to rate how strongly they agree with the statements. Scores for each item range from 0 to 2 points, and the maximum overall score is 80, with higher values indicating higher levels of empathy. For the current sample, internal consistency was good at α = 0.856.

Similar to Study 1, participants were tested individually and completed the study on Qualtrics. Upon arrival, they were informed that the aim of the study was to develop educational materials for job candidates wanting to improve their job interview skills. They were then provided with brief definitions of each smile type (genuine: “a smile displayed when someone is happy or amused and is truly feeling the emotion”; posed: “a smile that is intentional in the sense that someone wants to be nice and express positive intentions but does not feel the respective emotion”).

Prior to the smile evaluation task, we examined participants’ perceptions of the polite and happy contextual vignettes. Subjects were asked to imagine a person smiling during a job interview and after receiving a job offer, and to rate the extent to which both smiles would communicate that the person wanted “to be nice and to express positive intentions” (affiliation rating) or was “feeling happy and content” (happiness rating), using scales ranging from 0 to 100%. As in Study 1, participants’ responses across the two rating dimensions had to add up to 100%. After rating their beliefs about the meaning of smiles displayed in the polite and happy contexts, participants were randomly assigned to one of the two mimicry conditions. The restriction procedure was identical to the one used in Study 1.

The smile evaluation task involved the presentation of the 12 posed smiles (size: 360 × 480 pixels) in two blocks (each involving six photographs). The social context information was shown at the top of the screen together with each smile stimulus. To mirror the time course of the two scenarios, the first block always started with a description of the polite context (“This person is smiling during a job interview”), followed by the happy context description in the second block (“This person is smiling after receiving a job offer”). The selection of images in each block was counterbalanced across participants. We randomized presentation order within blocks, with every smile expression being displayed for 3 s. For each face-context pair, participants rated the extent to which the smile would communicate that the person wanted “to be nice and to express positive intentions” (ratings of affiliation, from 0 to 100%) or was “feeling happy and content” (ratings of happiness, from 0 to 100%). Again, both ratings were complementary and added up to 100%.

After completing the smile evaluation part, participants in the mimicry-restricted condition removed the pencil from their mouth. All participants then rated their mood on a scale ranging from 1 (“very negative”) to 7 (“very positive), and completed the EQ questionnaire (Baron-Cohen & Wheelwright, 2004 ). Both tasks lasted approximately 5 minutes.

Next, participants engaged in an unexpected two-alternative forced-choice smile discrimination task that examined how well subjects remembered the smiles they saw earlier in the experiment. On each trial, participants saw a posed smile from the first part of the experiment alongside a genuine smile (distractor stimulus) displayed by the same actor (sizes: 250 × 310 pixels). Importantly, each of these image pairs was accompanied by the context information, identical to the one provided with the posed smile earlier in the experiment. This information was presented at the bottom of the screen. The participants’ task was to indicate which of the two facial stimuli they had seen earlier. Thus, posed smiles were always the correct response, whereas genuine smiles were foils. Participants were informed that the context description was intended as a memory aid; but they were also instructed to base their judgments on their memories of the facial expression seen, rather than the social context information. Both the target and distractor image remained on the screen until participants submitted their response. We randomized the order of trials and counterbalanced the sides on which each type of smile appeared. Finally, participants were thanked and debriefed.

As in Study 1, we examined participants’ a priori beliefs about the type of smile expected in the two social context scenarios. A 2 (context: polite, happy) by 2 (mimicry: free, restricted) mixed ANOVA showed that, consistent with predictions, participants expected smiles paired with the polite context to communicate more affiliation ( M  = 76.48, SD  = 17.84) than smiles paired with the happy context ( M  = 21.41, SD  = 20.99), F (1, 64) = 283.95, p  < .001, η p ² = 0.82. The main effect of mimicry and the interaction between mimicry and context were not significant, F (1, 64) < 0.001, p  = .990, η p ² < 0.001 and F (1, 64) = 3.14, p  = .081, η p ² = 0.05, respectively. Adding mood and empathy as covariates in an ANCOVA did not change the pattern of statistical results and revealed no main effects of or interactions with the covariates ( F s < 3.42, p s > 0.068).

Ratings of affiliation were averaged across the stimulus faces and analyzed in a mixed ANOVA as a function of context and mimicry. The analysis revealed a main effect of context, F (1, 64) = 98.20, p  < .001, η p ² = 0.60, such that smiles were perceived as more affiliative when they appeared together with a polite ( M  = 67.72, SD  = 11.40) than with a happy context ( M  = 44.60, SD  = 13.15). The main effect of mimicry on perceived affiliation did not reach significance, F (1, 64) = 3.74, p  = .06, η p ² = 0.05. However, there was a significant interaction between context and mimicry, F (1, 64) = 5.29, p  = .025, η p ² = 0.08 (see Fig.  2 ). As expected, the impact of social context on smile ratings was stronger when facial mimicry was restricted (polite context: M  = 72.75, SD  = 11.40; happy context: M  = 44.05, SD  = 12.02, F (1, 64) = 72.35, p  < .001, η p ² = 0.53) than free (polite context: M  = 63.00, SD  = 14.58; happy context: M  = 45.12, SD  = 14.30, F (1, 64) = 29.86, p  < .001, η p ² = 0.32).

Ratings of affiliation as a function of social context and mimicry in Study 2. Error bars represent SEM

When controlling for mood and empathy as covariates in an ANCOVA, the main effect of context, F (1, 62) = 6.77, p  = .012, η p ² = 0.10, as well as the context by mimicry interaction, F (1, 62) = 4.70, p  = .034, η p ² = 0.07, remained significant. There were no main effects of or interactions with the covariates ( F s < 1.43, p s > 0.235).

Effects of Context and Mimicry on Smile Recognition Memory

Percentages of correctly identified posed smiles were averaged across the stimulus faces and analyzed in a mixed ANOVA as a function of context and mimicry. The main effect of context was significant, F (1, 64) = 5.18, p  = .026, η p ² = 0.08, such that a higher percentage of smiles was correctly identified as posed when they were presented together with a polite ( M  = 85.35%, SD  = 18.83%) than with a happy context ( M  = 77.27%, SD  = 26.98%). Mimicry had no effect on smile recall, F (1, 64) = 0.35, p  = .555, η p ² < 0.01, and the interaction between context and mimicry was not significant, F (1, 64) = 0.05, p  = .297, η p ² = 0.02.

An ANCOVA revealed no main effects of or interactions with mood and empathy as covariates ( F s < 1.40, p s > 0.263). However, the main effect of context was no longer significant, F (1, 62) = 1.39, p  = .243, η p ² = 0.02.

In Study 2, we investigated the joint influences of social context information and the ability to mimic on participants’ judgments and recognition memory of posed smiles. The findings replicate and extend the results of Study 1. As predicted, participants held specific beliefs about the meaning of smiles produced in a polite and happy context, and thought that the former were likely to communicate more affiliation. Furthermore, providing participants with labels describing such contexts affected the way they interpreted the posed smiles. Specifically, smiles were perceived as conveying more niceness and positive intentions and less happiness and contentment when they were paired with a polite rather than happy situation. Importantly, this influence of social context on smile judgments was stronger for participants whose mimicry was restrained, suggesting that they relied more on their conceptual knowledge. None of the above effects was modulated by empathy and mood, which points toward the critical role of mimicry beyond internal factors. It is also worth noting that restricting facial mimicry did not worsen recognition memory for smiles, suggesting that it is unlikely that the mimicry manipulation distracted participants from paying attention to the task. Interestingly, social context influenced the way participants remembered smiles, such that, when presented with a happy situation, subjects were more likely to erroneously report that they had earlier seen an enjoyment, not a posed smile. Although this result indicates that context information can affect the way information is retrieved, the effect became non-significant when controlling for empathy and mood in the analysis. This change, together with the generally high accuracy of participants’ responses in the memory task, suggest that more difficult questions are a promising avenue for future research examining how altering mimicry influences the memory of facial expressions.

General Discussion

The present research examined the influences of facial mimicry and social context information in the interpretation of non-enjoyment smiles. We tested these effects in two studies in which we altered participants’ facial activity using a standard pen-in-mouth manipulation and exposed them to employment-related descriptions of situations depicting happy and polite context. Participants judged the extent to which the smiles conveyed affiliation versus happiness and, in a task assessing recognition memory, indicated which smile they had seen earlier in the experiment. As predicted, our analyses revealed that in both studies participants perceived smiles as more affiliative when they were presented in a context associated with politeness than in a context judged as happy. In addition, context influenced smile recognition memory, such that participants were more likely to report seeing posed rather than genuine smiles when the recall task was accompanied by the polite (rather than happy) context information. These results are in line with previous research documenting the importance of verbal information on the processing of facial expressions (Barrett et al., 2007 ; Halberstadt & Niedenthal, 2001 ; Krumhuber et al., 2021 ; Namba et al., 2020 ). Our findings also confirm that people have specific beliefs about the types of smile appropriate in specific social situations and that this conceptual knowledge can shape the way they interpret and perceive smiles.

Furthermore, consistent with existing literature on sensorimotor simulation (e.g. Niedenthal et al., 2010 ; Wood et al., 2016b ), the two studies show that experimentally restricting facial mimicry can increase participants’ reliance on contextual information. This result is in line with the studies of Maringer and colleagues ( 2011 ), which, to our knowledge, were the only evidence of joint effects of sensorimotor simulation and social context on smile processing. Here, we extend these findings using more naturalistic stimuli presenting human actors rather than animated characters. We also tested the effects of mimicry restriction and contextual information on the perception of non-enjoyment posed smiles, therefore extending the research of Maringer and colleagues ( 2011 ) which focused on genuine smiles. In addition, both studies are confirmatory and adequately powered, which is particularly needed given the recent evidence on low reproducibility of research on facial feedback effects (Coles et al., 2019 ).

It is worth noting that, when exploring the discrimination between reward, affiliation, and dominance smiles, Orlowska et al. ( 2018 ) did not find a significant effect of restricting participants’ facial movements. One potential explanation of these seemingly inconsistent findings is that the present studies assessed the perceived meaning of a smile within a given situation, whereas in the study by Orlowska and colleagues ( 2018 ), participants were asked to categorize perceived expressions as instances of reward, affiliation, or dominance smiles. It is possible that facial mimicry, as well as other sensorimotor processes, may not be necessary to label the type of smile but plays an important role in different tasks, such as interpreting the meaning of a smile in a social situation. Another important factor could be the response format, with continuous slider scales allowing for more variability than categorical responses.

It is also worth highlighting that Maringer et al. ( 2011 , Study 2) did not observe a significant main effect of context. This could be due to the relatively low statistical power of this prior study, involving only 12 participants per condition. Another plausible explanation is the type of smile used. In the present studies, participants were asked to evaluate the meaning of non-enjoyment smiles, whereas genuine smiles served as target stimuli in the study by Maringer and colleagues. As non-enjoyment smiles are more ambiguous and challenging to classify than enjoyment smiles (Orlowska et al., 2018 ; Rychlowska et al., 2017 ), we believe that their judgment is more susceptible to the influence of contextual information. Such a tendency may be particularly marked for static stimuli which are more difficult to discern than dynamic expressions (Krumhuber et al., 2007 , 2013 ).

Both studies revealed consistent effects of context information on smile processing. In addition to showing that such information affects smile judgments, Study 2 reveals that verbal labels describing social situation may also affect participants’ ability to remember smiles. Specifically, compared with a happy situation, a polite situation made participants more likely to think that they have previously seen posed, not genuine smiles. Such results are in line with previous research (Woll & Martinez, 1982 ), which suggests that memorization of positive facial expressions is particularly vulnerable to verbal contextual information. Indeed, accurate memory for facial features presumably informs face perception (Tong & Nakayama, 1999 ), but it has been shown that both face perception and memory are malleable and subject to biases (Hugenberg & Sacco, 2008 ). For instance, social information about a target face can induce assimilation of the face to a categorical prototype, which influences how a face is perceived and remembered (Corneille et al., 2004 ; Hugenberg et al., 2011 ). Given that emotion expressions are often represented as categorical prototypes (i.e. prototypical emotion terms like “anger” or “fear” reflect cognitive representations in memory and language; Shaver et al., 1987 ), it is reasonable to expect that such assimilation processes also occur in the case of social context for facial displays. In other words, emotion expressions may be misremembered as having occurred in a social context more prototypical of the category (in this case: smile type).

We did not observe any effects of mimicry restriction in the recognition memory task. This finding suggests that verbal information affects smile processing to a greater extent than sensorimotor processes. In addition, the correct recollection of smiles, as required in the memory task, may be less sensitive to disruptions of sensorimotor processing than online judgments of these facial expressions. This result is in line with the findings from Kirkham and colleagues ( 2015 ), who showed that facial mimicry is reduced by inconsistent verbal information in the initial stages of encoding an expression but not when the same expression is viewed later.

Unlike the study of Maringer and colleagues ( 2011 ), the present experiments controlled for a number of potential confounds. Specifically, Study 2 included measures of participants’ empathy levels and mood and accounted for their joint effects (Jospe et al., 2018 ; Niedenthal et al., 2001 ; Sessa et al., 2018 ). The effects of restricting facial mimicry on participants’ smile judgments remained similar after controlling for these internal factors, suggesting that our findings cannot be explained by participants’ lower mood or empathy levels. However, the observed effect of context on recognition memory of smiles was no longer significant after adding empathy and mood as covariates. Thus, the influence of verbal information may vary depending on task demands and be less marked in remembering previously seen facial expressions rather than in interpreting the meaning of facial expressions when seeing them for the first time. Importantly, we did not find main effects of mimicry condition on participants’ ratings in any of the two studies, making it unlikely that altering facial movements distracted participants from paying attention to the task. Such an interpretation was also discarded by the study of Rychlowska and colleagues ( 2014 ), who showed that judgments of smile genuineness can be disrupted by restricting mimicry but not by other distracting tasks (i.e., holding a squeeze ball or wearing a finger-cuff heart rate monitor). One limitation of the present studies, as well as much of the existing literature on facial mimicry, concerns the limited information about the extent to which the pen-in-mouth paradigm actually impacts participants’ facial activity. Measuring those effects more explicitly and establishing guidelines for blocking facial mimicry is an important challenge for future research. Another challenge is examining how the influence of mimicry manipulations on the accuracy of smile judgments varies depending on different smiles and contexts. For example, which contexts are most influential? How would contextual vignettes affect real social interactions when mimicry is not possible?

To our knowledge, our studies are the first to experimentally test the joint influences of social context and restricting facial mimicry on the processing of smiles displayed by human actors. Our findings reveal that people hold specific beliefs about the likelihood of observing non-enjoyment and enjoyment smiles in different social contexts and that this knowledge is used to guide the interpretation and the memory of smiles. Importantly, this influence is particularly strong when participants’ facial mimicry is inhibited by holding a pen in the mouth. The present results have important implications for everyday life, offering insights into mechanisms guiding facial expression processing in clinical populations, such as patients with facial palsy or persons whose facial mimicry is altered due to reduced social motivation (Bourgeois & Hess, 2008 ). By investigating the interplay of social context and sensorimotor processes, the present research is an important first step in this direction and provides promising avenues for future research.

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Acknowledgements

The authors thank Inez Bawa, Weronika Kowalczyk, Iqra Malik, Luca Michael, Katarzyna Myszkowska, Sorelle Oates, Maya Rampal, Sabina Raus, Antonia Toneva for their help with data collection and Bronagh Allison for editing the manuscript.

This research was supported by an internal grant for young scientists from the Institute of Psychology of Polish Academy of Sciences awarded to Anna Orlowska (IP PAN 2015 and IP PAN 2017).

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Functionally distinct smiles elicit different physiological responses in an evaluative context

• Jared D. Martin 1 ,
• Heather C. Abercrombie 2 ,
• Eva Gilboa-Schechtman 3 &
• Paula M. Niedenthal 1  

Scientific Reports volume  8 , Article number:  3558 ( 2018 ) Cite this article

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When people are being evaluated, their whole body responds. Verbal feedback causes robust activation in the hypothalamic-pituitary-adrenal (HPA) axis. What about nonverbal evaluative feedback? Recent discoveries about the social functions of facial expression have documented three morphologically distinct smiles, which serve the functions of reinforcement, social smoothing, and social challenge. In the present study, participants saw instances of one of three smile types from an evaluator during a modified social stress test. We find evidence in support of the claim that functionally different smiles are sufficient to augment or dampen HPA axis activity. We also find that responses to the meanings of smiles as evaluative feedback are more differentiated in individuals with higher baseline high-frequency heart rate variability (HF-HRV), which is associated with facial expression recognition accuracy. The differentiation is especially evident in response to smiles that are more ambiguous in context. Findings suggest that facial expressions have deep physiological implications and that smiles regulate the social world in a highly nuanced fashion.

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Introduction.

Sweaty palms, a racing heart, a faltering voice. Most people find the evaluative context of public speaking unpleasant. Indeed, the mere anticipation of social evaluation increases activity across almost all body systems related to stress, with particularly robust activation in the hypothalamic-pituitary-adrenal (HPA) axis 1 , 2 , 3 , 4 . However, scientific inquiry has largely been limited to investigations of the manner in which the body responds to verbal evaluative feedback, of the type “that was/wasn’t good.” 5 , 6 Does the HPA axis respond to purely nonverbal feedback, such as facial expression? We investigate this question and demonstrate that evaluators’ smiles are sufficient to augment or dampen HPA axis activity – depending upon the distinct meaning of the smile in the social-evaluative context. Furthermore, we find that physiological responses to smile meaning are most differentiated in individuals with higher baseline high-frequency heart rate variability (HF-HRV), which is associated with facial expression recognition accuracy 7 , 8 , 9 .

Nonverbal feedback in social-evaluative contexts should be at least as impactful as verbal feedback, since nonverbal signals are experienced by perceivers to be spontaneous reactions 10 and thus, honest reflections of internal evaluations. In the few studies that have investigated the nonverbal communication of evaluative feedback, participants whose audience displayed smiles and other nonverbal expressions of positive evaluation showed lower physiological activity than participants met with frowns and similar cues to negative evaluation 11 , 12 , 13 . Recent theory and empirical evidence suggests, however, that smiles do not all communicate identical, uniformly positive messages 14 , 15 , 16 . Instead, evidence supports the existence of at least three morphologically distinct types of smiles, each of which serves a different social function necessary for successful group living: “reward” smiles reinforce behavior, “affiliation” smiles signal lack of threat and facilitate or maintain social bonds, and “dominance” smiles assert claims to higher status in social hierarchies 15 , 16 . In light of their social functions, each of these three smiles should carry distinct meanings when displayed by evaluators. The first aim of the present research was to test the hypothesis that reward, affiliation, and dominance smiles, delivered as evaluative feedback, influence perceivers’ HPA axis activity in a manner congruent with their distinct social meaning. We expected dominance smiles, compared to reward smiles, to increase HPA axis activity. In theory, whereas dominance smiles show disdain for and reward smiles show approval of performance, affiliation smiles reassure without being indicative of a specific evaluation and so were expected to buffer HPA axis activity to a lesser degree than reward smiles.

The second aim of the present research was to account for variability in participants’ capacity to understand the evaluative meanings of each smile. Reward smiles are more unambiguous in meaning across contexts than either affiliation or dominance smiles 14 , which are relevant in more limited contexts. That is, reward smiles can reinforce widely varying behaviors in most any social situation, whereas affiliation smiles serve to smooth existing or potential social bonds and dominance smiles serve to challenge social standing. Individuals who are more accurate at recognizing facial expressions should exhibit more differentiated physiological activity in response to affiliation and dominance smiles, indicating greater sensitivity to their social-evaluative meanings. Recent empirical evidence suggests that baseline HF-HRV – an index of parasympathetic nervous system activity at the level of the heart – is positively associated with facial expression recognition accuracy 7 , 8 , 9 . We thus tested the hypothesis that individuals with higher baseline HF-HRV exhibit more differentiated physiological activity in response to smiles presented as evaluative feedback, particularly in response to smiles that are more ambiguous in context (i.e., affiliation and dominance smiles).

In an adaptation of the classic Trier Social Stress Test 17 , male participants ( N  = 90) extemporaneously addressed three topics about themselves in front of a male evaluator who watched them over a web camera. The evaluator was, in fact, one of two confederates working for the research team; approximately half of the participants ( N s = 47 and 43) interacted with each confederate. To increase believability, the evaluator briefly appeared live on the computer screen, then turned off his web camera for the remainder of the session. After responding to each of the three topics, participants saw videos of their evaluator’s facial expressions, which they believed represented spontaneous reactions to their performance that had been extracted by facial recognition software. The videos were, in fact, pre-recorded. Participants were assigned to one of three smile conditions such that they saw either one reward, affiliation, or dominance smile after each of their responses to the three topics. Along with one smile video, participants also saw a control video that showed the evaluator making a neutral response such as face scratching or eye blinks. Thus, each participant was exposed to six videos of their evaluator in total (three different instances of one type of smile, three neutral videos) with one smile and one neutral video presented after each of the three responses. Smile videos were constructed to meet a priori specifications of morphological activity associated with each of the three smile types (for further details, see Supplementary Materials ) 14 . Thus, smile type was the only feature of the evaluative feedback that varied between conditions. Physiological activity, in both the HPA axis and cardiovascular system, was assessed throughout the study; salivary cortisol was measured at seven time points, and a continuous electrocardiograph was collected before, during, and after the speech task.

Raw means for total salivary cortisol level by smile condition were consistent with the prediction that reward, affiliation, and dominance smiles influence perceivers’ physiological activity in distinctive ways, such that the receipt of dominance smiles is associated with higher HPA axis activity relative to the receipt of reward smiles. (AUC i – nmol/l: dominance: M  = 19.4, SD  = 24.74; affiliation: M  = 2.43, SD  = 22.3; reward: M  = 1.21, SD  = 21.54). We used dummy-coded condition contrasts to directly compare total salivary cortisol responses between smile types (“ AUCi ”, see Methods, below). Compared to reward smiles, dominance smiles induced a greater overall salivary cortisol response ( b  = 18.18, t (86) = 2.93, p  = 0.004, CI (95%) = [5.83, 30.54], Δr 2  = 0.087). Similarly, even though affiliation smiles do not signal a clear social evaluation in this context, compared to such smiles, dominance smiles induced a greater overall salivary cortisol response ( b  = 16.97, t (86) = 2.92, p  = 0.004, CI (95%) = [5.41, 28.53], Δr 2  = 0.086).

Further corroborating the finding that dominance smiles induce greater HPA axis activity, participants receiving reward or affiliation smiles returned to their individual cortisol baseline by 30-minutes post-speech, whereas those who received dominance smiles continued to have significantly higher cortisol levels than their individual baseline. In this ancillary analysis, cortisol values at 20- and 30-minutes post-speech were predicted from dummy-coded condition contrasts and average baseline cortisol level. Intercepts for each smile condition at both 20-minutes post-speech (reward, b  = 0.23, t (86) = 1.49, p  = 0.14, CI (95%) = [−0.08, 0.53]; affiliation, b  = 0.25, t (86) = 1.79, p  = 0.08, CI (95%) = [−0.03, 0.53]; dominance, b  = 0.57, t (86) = 4.47, p  < 0.0001, CI (95%) = [0.31, 0.82]) as well as 30-minutes post-speech (reward, b  = −0.02, t (86) = −0.13, p  = 0.9, CI (95%) = [−0.32, 0.28]; affiliation, b  = 0.03, t (86) = 0.2, p  = 0.84, CI (95%) = [−0.25, 0.31]; dominance, b  = 0.36, t (86) = 2.82, p  = 0.006, CI (95%) = [0.11, 0.61]) show that mean salivary cortisol values for the dominance group continued to be significantly greater than zero up to 30-minutes post-speech, which was not the case for the other groups. This shows that individuals receiving dominance smiles take significantly longer to return to their individual cortisol baseline, thus corroborating findings from the AUC i analysis.

We also tested the prediction that baseline HF-HRV is positively associated with differentiation in HPA axis activity in response to affiliation and dominance smiles. We again created dummy-codes for smile feedback condition in order to compare the effect of smile feedback between conditions. We entered these dummy-codes along with a continuous measure of baseline HF-HRV and the dummy-code by HF-HRV interaction terms into a linear regression model. Results from this analysis confirmed our expectations. With those who received dominance smiles as the dummy-coded reference group, baseline HF-HRV was positively correlated with salivary cortisol responses ( b  = 9.72, t (84) = 2.02, p  = 0.046, CI (95%) = [0.14, 19.29], Δr 2  = 0.04). Comparing the linear association between baseline HF-HRV and salivary cortisol responses between individuals who received dominance versus affiliation smiles, the comparison of simple slopes was significant ( b  = 14.63, t (84) = 2.40, p  = 0.018, CI (95%) = [2.54, 26.83], Δr 2  = 0.057), indicating that the relationship between baseline HF-HRV and salivary cortisol is more positive for those receiving dominance compared to affiliation smiles as evaluative feedback (Fig.  1 ).

Physiological Response to Smiles as Evaluative Feedback Depends on Baseline High Frequency Heart Rate Variability. Salivary Cortisol : Total salivary cortisol (nmol/l: dominance: M  = 19.4, SD  = 24.74, N  = 27; affiliation: M  = 2.43, SD  = 22.3, N  = 36; reward: M  = 1.21, SD  = 21.54, N  = 27) in response to social evaluation was greater for those receiving dominance smiles as evaluative feedback relative to the two other types of smiles. The difference in total salivary cortisol response between the affiliation and dominance groups increased as HF-HRV increased. Heart Rate : Heart rate assessed during the speech task (bpm: dominance: M  = 83.51, SD  = 9.84, N  = 27; affiliation: M  = 82.13, SD  = 14.43, N  = 36; reward: M  = 85.93, SD  = 12.65, N  = 27) was not significantly different between conditions. The difference in heart rate between the dominance and affiliation groups increased as HF-HRV increased. Dotted lines between the +/− 1 SD bars indicate a statistically significant simple slope for baseline HF-HRV in that feedback condition; solid lines are not significant below the 0.05 level.

Convergent evidence that baseline HF-HRV is positively associated with greater differentiation of physiological responses to affiliation and dominance smiles comes from cardiovascular data. Again, we created dummy-coded condition contrasts and entered them into a linear regression model along with baseline HF-HRV and the HF-HRV by smile feedback dummy-code interaction terms. With the dummy-coded condition contrasts referenced on participants who received affiliation smiles, baseline HF-HRV was negatively associated with heart rate during the speech task ( b  = −5.84, t (84) = −2.85, p  = 0.006, CI (95%) = [−9.91, −1.76], Δr 2  = 0.086). A comparison of the linear association between baseline HF-HRV and heart rate between individuals who received affiliation versus dominance smiles reveals that the relationship between baseline HF-HRV and heart rate was more negative for those exposed to affiliation compared to dominance smiles as evaluative feedback ( b  = −7.28, t (84) = 2.19, p  = 0.032, CI (95%) = [−13.92, −0.66], Δr 2  = 0.051).

Since indicators of HF-HRV reactivity (i.e., baseline – task) have also been associated with facial expression recognition accuracy 18 , we conducted ancillary analyses of the association between reactivity measures of HF-HRV and perceivers’ physiological activity in response to smile feedback. Specifically, we calculated a difference score between task level HF-HRV and baseline by subtracting task HF-HRV, assessed during the first 2.5 minutes of the speech, from baseline HF-HRV. Higher values on this difference score reflect greater withdrawal of vagal influence over the heart during task, compared to baseline. We entered the difference score into a model similar to the one employed in the cortisol and heart rate analyses, entering dummy-coded condition contrasts along with the continuous HF-HRV difference score and the condition by difference score interactions. Table  1 reports these findings. HF-HRV reactivity was positively associated with physiological responses to social evaluation, regardless of the type of smile feedback a participant received (i.e., HF-HRV reactivity did not interact with experimental condition: see Table  1 ). These findings strengthen the conclusion that higher baseline HF-HRV is associated with more differentiated physiological responses to smiles as evaluative feedback.

Analyses were conducted in the “R” statistical environment 19 . All results reported in the present work remain significant when adding a dichotomous predictor to account for which of the two confederates a participant interacted with, as well as when statistically accounting for factors known to influence levels of physiological activity (caffeine use, depression severity).

In the present study, we observed that smiles with different social functions 16 , when delivered as evaluative feedback in a stressful social context, exert distinct influences on perceivers’ physiological activity. Dominance smiles (compared to reward or affiliation smiles) were associated with increases in heart rate and salivary cortisol that mirror the influences of negative verbal feedback 20 . In contrast, reward and affiliation smiles exerted influences similar to the effects of displays of friendliness 21 and positive social evaluation 12 , such that, compared to dominance smiles, they buffered physiological activity. The findings thus provide further evidence for the view that smiles do not constitute a homogenous category of “positive” nonverbal feedback. The findings also contribute to a body of literature that proposes a role for cortisol in adaptive responding to the social environment 22 . In particular, cortisol appears to support the detection of social threat and coordinate biological activity needed to adequately respond to the threat.

The present research also contributes to a growing literature on individual differences in sensitivity to the meaning of facial expression. Specifically, baseline HF-HRV was negatively related to participants’ physiological activity when they received affiliation smiles, and was positively related to their physiological activity when they received dominance smiles as evaluative feedback. The observed relationship between HF-HRV and physiological responsiveness to specific smile meaning is consistent with a claim of the Neurovisceral Integration Model according to which HF-HRV indexes an individual’s capacity to respond appropriately to social stimuli 23 . Conversely, individuals with particularly low baseline HF-HRV may be at risk of poor socio-emotional outcomes due to deficits in both understanding as well as responding to the social signals of others. A number of pathological and pre-disease body states are related to lower HF-HRV, including heightened inflammation and obesity 24 , 25 . As such, these body states may fundamentally change an individual’s ability to respond physiologically to the social world, and in light of the present findings, may be associated with deficits in understanding the expressions of others. A compelling avenue for future research therefore is to investigate how individuals with relatively low HF-HRV recognize and respond to the expressions of others.

Future research should also consider how affective disorders associated with lower HF-HRV, such as anxiety 26 and depression 27 , relate to cognitive and physiological responses to social stimuli. Given the social stress procedure implemented in the present work, an especially fruitful avenue for future research on the social functions of smiles lies in the relationship between smile processing and social anxiety. Social anxiety disorder involves the fear of embarrassing oneself in front of others in performance or evaluative situations 28 . Although research consistently documents that individuals with social anxiety disorder exhibit heightened negative affect both in anticipation of and in response to social evaluation 29 , 30 , findings are mixed 31 , 32 regarding how these individuals respond to positive and supportive social signals. Social anxiety was not accounted for in the present study. Although randomization into condition likely mitigated any effect of social anxiety on the present findings, future work is needed to investigate how individuals with social anxiety respond to facial expressions as evaluative feedback. A crucial comparison in this work will be to assess differences in affective and physiological responses between the relatively unambiguous reward smiles and the less clear affiliation smiles.

One limitation of the present research is that the experimental design contained no “neutral” feedback condition. It would be hard to create such an experience, since neutral feedback is interpreted in highly varied ways across individuals. However, methods to create such a control condition could be imagined for future research. Along similar lines, future research could also directly compare the effects of receiving dominance smiles with the effects of receiving more overt signals of negative evaluation such as disgust, contempt, and anger. By employing the present paradigm to test the physiological effects of facial expressions beyond the smiles tested here, researchers could not only more clearly describe the unique effects of receiving social functional smiles but also understand the effects of facial expressions on perceivers’ physiological activity more generally.

The present work includes other limitations that warrant comment, two of which concern the participant sample. First, the sample size in this study may have been relatively small given the size of the effects detected. Since, to our knowledge, no work has explored the effect of receiving social functional smiles as social evaluation, a priori power analyses were difficult to conduct. We estimated required sample size from extant studies with methods and aims as similar to the present research as possible 12 . Following these guidelines, 90–100 participants is typical for a study of this nature involving three between-subjects conditions. Post-hoc power analyses using G*Power 33 indicate that achieved power was modest for the critical comparisons within the HPA axis (dominance vs. affiliation: β = 0.72; dominance vs. reward: β = 0.81). In light of the achieved power, we recommend that future studies of this sort rely on no fewer than 35–40 participants per between-subjects condition to ensure adequate power.

Second, the present sample was restricted to men. Although we limited the sample to males for reasons that were established and justified before the research was conducted (see Methods, below), generalizations from our findings are necessarily limited. Since sex effects are observed in research on the perception of facial expression of emotion 34 , 35 , future work should determine what portion (if any) of the currently documented effects are contingent upon the sex of the smiler or perceiver. Some work suggests that men respond more to threats of physical aggression whereas women respond more to condescending behaviors and social aggression 36 . Thus, men and women may respond to the same type of smile in different ways and may also use each of the smile types with varying degrees of frequency 37 .

The present research demonstrates that functionally different smiles are sufficient to augment or dampen HPA axis activity in accordance with the social functional meaning associated with each smile. Furthermore, physiological responses to each functionally distinct smile are most differentiated in individuals with higher baseline HF-HRV, suggesting that HF-HRV is a useful individual difference moderator of the ability to respond to the social environment in a flexible and nuanced fashion. We may therefore conclude that smiles coordinate the physiological activity that supports interpersonal encounters to a previously undocumented degree, and that facial expressions help regulate the social world, in part, through their impact on the physiological activity of perceivers.

Participants

Ninety-two male undergraduates at a large university in the Midwest participated in exchange for credit in an introductory Psychology course. Participants provided written consent, indicating full understanding of the requirements for participation. The research protocol was reviewed and approved under the University of Wisconsin – Madison Institutional Review Board. All research was conducted in accordance with institutional guidelines and regulations.

Due to the robust sex differences in cortisol responses to laboratory stressors 38 and the variability in cortisol responses introduced by oral contraceptive use 39 , only males were invited to participate in this study. Since females generally outperform males in the accurate recognition of positive facial expressions 40 , the expectation was that the present study would underestimate the effects of smiles on physiological responses. Pre-inclusion criteria limited participation to U.S.-born, English-speaking males without a diagnosed heart condition and not currently taking medications that alter hormone levels. Participants were instructed to refrain from exercise on the day of the study and to avoid alcohol and caffeine consumption within twenty-four hours of their participation. Due to a network failure, data collection from one participant was terminated before experimental manipulation. Furthermore, data from a second participant were excluded from analysis due to the presence of an abnormal heart rhythm resembling premature beats 41 which made it difficult to score the data and conflicted with the pre-inclusion criterion of cardiac health. The exclusion of all data from these two participants left a final sample of ninety participants (dominance: N  = 27; affiliation: N  = 36; reward N  = 27).

Data collection was limited to the number of participants that could be involved during one academic semester, not to exceed 120 participants (40 per condition). Participants were randomly assigned to one of three smile experimental conditions as well as one of two confederates. Given that some participants did not show up for their assigned experimental sessions, a certain amount of imbalance between the number of participants in each condition and assigned to each confederate is to be expected.

At the conclusion of the study, participants underwent a funneled debriefing. First, they were asked if they thought they knew what the study was about. In this general interview, no participants brought up suspicions about deception. We then asked participants if they found anything strange about the study or were suspicious of anything. In a logistic regression model with experimental condition and confederate as predictors of a dichotomous (“yes”/“no”) suspicion outcome, no significant differences were detected by experimental condition (all p s > 0.2) or by confederate ( p  = 0.93). Participants who thought the study was slightly strange indicated that they were unsure how the filler video was related to the study, were unaccustomed to providing saliva samples, or were uncomfortable giving speeches.

In order to reduce variation due to diurnal changes in cortisol levels, experimental sessions took place in the afternoon. Upon arriving at the experimental laboratory, the participant encountered another male “participant” who was actually a confederate—one of the two whose stimuli were validated in a separate study (see Supplemental Material for further information). The experimenter then entered from a nearby room and told the two men that he had randomly assigned them to different tasks in the study: the participant was always assigned to “give the speech” and the confederate was always assigned to “judge the speech.” After the participant and confederate had provided informed consent, the participant supplied the first of seven saliva samples (collection method described below) and completed an online questionnaire assessing his compliance with pre-restriction criteria (alcohol and caffeine use) as well as other medical information (prescription and recreational drug use). The men were told that only the person giving the speech (always the participant and never the confederate) had to answer the online questionnaires and provide the saliva samples because it directly pertained to giving the speech; the confederate waited with the participant and the experimenter while the participant responded to the surveys and provided the saliva sample.

The experimenter then demonstrated a facial expression recognition software, the Computer Emotion Recognition Toolbox 42 . The participant and confederate were informed that the program could extract meaningful facial expressions from live video feed. The experimenter used the computer’s built-in web camera and the participant’s face as the live feed in a demonstration in order to increase believability in the software’s (actual) capabilities.

Next, the participant and confederate were separated. Leaving the confederate behind in the initial room, the experimenter mentioned that a second experimenter would arrive shortly to provide the confederate with further instructions and tasks. The experimenter escorted the participant to a psychophysiology lab in the same building. There, the experimenter attached sensors to the participant’s chest and explained that they would be used to measure aspects of his cardiovascular reactivity. The experimenter sat with the participant in the experimental room while a research assistant in an adjacent control room recorded a 3-minute baseline measure of the participant’s heart activity.

After completion of this baseline recording, the experimenter informed the participant that he would deliver his speech to the “other participant” via Skype. He would not see the evaluator as his web camera would be turned off in order to avoid distraction. The format of the speech involved answering three questions in sequence, with two minutes to respond to each question. The participant was also told that at the conclusion of every two-minute speech period, he would see videos of several of the evaluator’s facial expressions. The participant was told that the videos had been “randomly extracted by the facial expression software” while the evaluator watched the participant’s speech. This led the participant to believe that the videos conveyed authentic evaluative responses by the confederate. The facial expressions displayed in these videos constituted the experimental manipulation.

When the participant indicated that he had understood the speech task, the experimenter gave him a sheet of paper with the three questions he was required to answer, and then sat with the participant for three minutes while the participant prepared his speech. A continuous cardiovascular recording was taken during this three-minute “anticipation” period. After the time was over, the second saliva sample was taken.

Next, the experimenter launched Skype. In order to enhance believability, the confederate appeared live on the participant’s screen and waved “hello.” The experimenter asked the evaluator to turn off his camera “so as not to distract” the participant during the speech. With the participant no longer able to see the evaluator, the experimenter asked the participant to begin his speech. Participants responded to each question in order, with two minutes for each question: (1) What makes you happy? (2) What do you like most and least to eat?, and (3) What is your favorite part of living in Madison, Wisconsin? These questions were designed to be personal and to contain enough positive material to make the smiles sent by the evaluator appear plausible.

At the conclusion of each two-minute speech period, the experimenter stopped the participant and showed him two videos of the evaluator that were “randomly extracted” when he was listening to the participant’s speech. From the other room, the confederate dropped each video into a network-based folder in order to simulate the facial expression recognition program extracting and sending the videos in real time. Each participant saw 6 videos in total, 2 after each question. 3 of the 6 total videos were smiles and the other 3 were a set of different neutral videos—evaluators faced the camera with a neutral expression and made occasional small, non-evaluative movements such as face scratching. The smile videos were three different short video clips of the same confederate making only one smile type (dominance, reward, or affiliation). Participants were thus exposed to three different examples of the same type of smile. In sum, smile type was manipulated between-subjects with the 3 neutral videos retained across participants. At the conclusion of the speech task, the third saliva sample was taken. The speech task lasted between 7–8 minutes, during which a continuous cardiovascular recording was taken.

Immediately upon concluding his final speech, the participant was directed to reflect on his performance, focusing on how he felt and what his evaluator thought. A continuous cardiovascular recording was taken during this five-minute reflection period. After the reflection/recovery period, the participant was detached from the sensors and led to the final room by a second experimenter who was blind to the participant’s video feedback condition.

In the last room, the participant watched a filler video available on YouTube from the series “The Life of Birds” (available at https://www.youtube.com/playlist?list=PLB1F251E81DE15E9B ) which provided a neutral experience during which cortisol recovery was assessed. The video was the same for all participants. The remaining four saliva samples were taken at 10-minute intervals from the cessation of the speech task. At the conclusion of the filler video, and after completing verbal questions assessing deception suspicion, the participant was debriefed and dismissed.

Physiological Measures: Collection and Analysis

Saliva samples were obtained with cotton salivettes (Fisher Scientific Company, LLC). Participants were instructed to let the cotton salivette touch all parts of their mouth (under their tongue, between their teeth and their cheeks) without chewing on it. Saliva collection was strictly timed for two minutes, after which the sample was returned to its plastic casing. Samples were frozen after collection and stored at −20 C. At the conclusion of the study, samples were express shipped to Dresden, Germany where they were single-assayed at the lab of Dr. Clemens Kirschbaum (T.U. Dresden). Samples were assayed using the chemi-luminescence assay, which has a high sensitivity of 0.16 ng/mL (IBL-International, Hamburg, Germany) and intra and interassay CVs of <10%. In total, saliva samples were collected at seven time points during the study and assayed for unbound cortisol. Due to skewness, all cortisol values were first log-transformed. Salivary alpha amylase was assayed but is not reported in these analyses.

In order to test our hypotheses with regard to the HPA axis, Area Under the Curve with respect to increase (AUC i ) 43 values were calculated for the cortisol response of each participant. AUC i scores index total cortisol response over a given period of time, referenced to each individual’s baseline cortisol level. We averaged the two cortisol values collected before experimental manipulation (receipt of smile feedback) as a pre-speech baseline.

Continuous EKG recordings were sampled at 1000 Hz via one of the bipolar inputs available on the SynAmps2 Headbox (Compumedics Neuroscan Ltd., U.S.A). Ag/AgCl spot electrodes were placed in a thoracic-modified lead-II configuration to maximize detection of R-spikes while minimizing movement artifacts. We calculated mean heart rate values separately for the baseline period, the “anticipation” period, the speech period, and the post-speech period.

Data Processing

EKG data were first scored offline using OpenANSLAB 44 , manually inspected for artifacts, and the resultant inter-beat-interval series were extracted and saved. CMETx software (available at http://apsychoserver.psych.arizona.edu ) was then used on the extracted inter-beat-interval to quantify HF-HRV.

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Acknowledgements

The authors would like to thank Craig Berridge, Allison Blumenfeld, Stephanie Carpenter, Crystal Hanson, Judy Harackiewicz, Roxanne Hoks, Cathy Marler, and Wendy Berry Mendes for their assistance and helpful comments. Magdalena Rychlowska and Adrienne Wood provided critical feedback during the revision process. Stella Mayerhoff, Josh Lucas, Sarah Hervdejs, and Mathias Hibbard were instrumental in collecting data. We also acknowledge the tireless contribution of our two confederates A.J. Laird and Zeus Markos. This work was supported by the National Institutes of Mental Health [grant number T32MH018931-26 to J.D.M]; the U.S. – Israeli Binational Science Foundation [grant number 2013205 to P.M.N. and E.G.S.]; and the National Science Foundation [grant number 1355397 to P.M.N.]. Further support for this research was provided by the Graduate School and the Office of the Vice Chancellor for Research and Graduate Education at the University of Wisconsin-Madison with funding from the Wisconsin Alumni Research Foundation. Sources of financial support had no influence over the design, analysis, interpretation, or choice of submission outlet for this research. Data are available by contacting the corresponding author.

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Martin, J.D., Abercrombie, H.C., Gilboa-Schechtman, E. et al. Functionally distinct smiles elicit different physiological responses in an evaluative context. Sci Rep 8 , 3558 (2018). https://doi.org/10.1038/s41598-018-21536-1

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Smiling is the secret to seeing happiness, new research reveals

Smiling for just a split second makes people more likely to see happiness in expressionless faces, new University of Essex research has revealed.

The study led by Dr Sebastian Korb, from the Department of Psychology, shows that even a brief weak grin makes faces appear more joyful.

The pioneering experiment used electrical stimulation to spark smiles and was inspired by photographs made famous by Charles Darwin.

A painless current manipulated muscles momentarily into action -- creating a short uncontrollable smile.

This is the first time facial electrical stimulation has been shown to affect emotional perception.

Dr Korb hopes the research can explore potential treatments for depression or disorders that affect expression, like Parkinson's and autism.

He said: "The finding that a controlled, brief and weak activation of facial muscles can literally create the illusion of happiness in an otherwise neutral or even slightly sad looking face, is ground-breaking.

"It is relevant for theoretical debates about the role of facial feedback in emotion perception and has potential for future clinical applications."

Dr Korb used a modernised version of a technique first developed in the 19th century by the French physician Duchenne de Boulogne.

Darwin published drawings of Duchenne's work in The Expression of the Emotions in Man and Animals -- his third major work on evolution.

However, the voltage was dialled down for the new experiments to ensure the safety of participants and better control the smiles.

By using computers, the team were able to control the onset of smiles with millisecond precision.

In total 47 people took part in the Essex study which was published in Social Cognitive and Affective Neuroscience.

They were shown digital avatars and asked to assess whether they looked happy or sad. In half the trials, smiling muscles were activated at the onset of the face.

It emerged that producing a weak smile for 500 milliseconds was enough to induce the perception of happiness.

Dr Korb says the results help us understand facial feedback and he hopes to expand the study.

He said: "We are currently conducting more al research to further explore the phenomenon in healthy participants.

"In the future, however, we hope to apply this technique to explore facial emotion recognition, for people with conditions like Parkinson's, who are known to have reduced spontaneous facial mimicry and impaired facial emotion recognition.

"Moreover, we have published guidelines to allow other researchers to safely start using electrical facial muscle stimulation."

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• Themis Nikolas Efthimiou, Joshua Baker, Alasdair Clarke, Arthur Elsenaar, Marc Mehu, Sebastian Korb. Zygomaticus activation through facial neuromuscular electrical stimulation (fNMES) induces happiness perception in ambiguous facial expressions and affects neural correlates of face processing . Social Cognitive and Affective Neuroscience , 2024; 19 (1) DOI: 10.1093/scan/nsae013

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A posed smile can improve your mood, new research suggests

Scientists say the findings provide useful insight into what emotions are and where they come from., article bookmarked.

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A posed smile can improve your mood suggesting that it may be possible to smile your way to happiness, a new study suggests.

Psychologists have long questioned whether facial expressions influence people’s emotional experiences – an idea known as the facial feedback hypothesis.

An international collaboration of researchers, led by Stanford University research scientist Nicholas Coles, have found strong evidence that posed smiles can, in fact, make us happier.

However, the study found the effect is not strong enough to overcome something like depression.

This research tells us something fundamentally important about how this emotional experience works

But it provides useful insight into what emotions are and where they come from, the scientists say.

Dr Coles said: “We experience emotion so often that we forget to marvel at just how incredible this ability is.

“But without emotion, there’s no pain or pleasure, no suffering or bliss, and no tragedy and glory in the human condition.

“This research tells us something fundamentally important about how this emotional experience works.”

Despite the findings, psychologists still are not sure about why the body works in this way.

But one theory is that our conscious experience of emotions is based off sensations in the body – the idea that the feeling of a rapid heartbeat provides some of the sensation we describe as fear, for example.

Facial feedback has often been cited as evidence for this theory, but some recent experiments have called it into question.

For the study, researchers created a plan that included three well-known techniques intended to encourage participants to activate their smile muscles.

One-third of participants were asked to use the pen-in-mouth method, and one-third were asked to mimic the facial expressions seen in photos of smiling actors.

The final third were given instructions to move the corners of their lips toward their ears and lift their cheeks using only the muscles in their face.

In each group, half the participants performed the task while looking at cheerful images of puppies, kittens, flowers and fireworks, and the other half simply saw a blank screen.

They also saw these same types of images, or lack thereof, while directed to use a neutral facial expression.

We’re closer than ever to understanding a fundamental part of the human condition: emotion

To disguise the purpose of the study, researchers mixed in several other small physical tasks and asked participants to solve simple math problems.

After each task, participants rated how happy they were feeling.

The Many Smiles Collaboration collected data from 3,878 participants from 19 countries.

After analysing the data, researchers say they found a noticeable increase in happiness from people mimicking smiling photographs or pulling their mouth toward their ears.

But similar to a 2016 study group, they did not find a strong mood change in participants using the pen-in-mouth technique.

Dr Coles said: “The stretch of a smile can make people feel happy and the furrowed brow can make people feel angry; thus, the conscious experience of emotion must be at least partially based on bodily sensations.

“Over the past few years, the science took one step back and a few steps forward.

“But now we’re closer than ever to understanding a fundamental part of the human condition: emotion.”

The findings are published in the Nature Human Behaviour journal.

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Global collaboration led by Stanford researcher shows that a posed smile can improve your mood

Can posing a smile brighten our mood? According to an international collaboration of researchers, the answer is yes.

When we’re happy, we smile. The corners of our mouths move out and up, our cheeks lift, and the skin around our eyes crinkles. But does it work the other way? Can posing our muscles in a smile brighten our mood?

According to an international collaboration of researchers, posing a smile can brighten our mood. (Image credit: Getty Images)

This question has been part of a long-standing debate among psychology researchers about whether facial expressions influence our emotional experience, an idea known as the facial feedback hypothesis. In a recent paper published in Nature Human Behavior , an international collaboration of researchers led by Stanford research scientist Nicholas Coles found strong evidence that posed smiles can, in fact, make us happier.

The effect isn’t strong enough to overcome something like depression, said Coles, but it provides useful insight into what emotions are and where they come from.

“We experience emotion so often that we forget to marvel at just how incredible this ability is. But without emotion, there’s no pain or pleasure, no suffering or bliss, and no tragedy and glory in the human condition,” he added. “This research tells us something fundamentally important about how this emotional experience works.”

Psychologists still aren’t sure about the origins of this central part of the human condition. One theory is that our conscious experience of emotions is based off sensations in the body – the idea that the feeling of a rapid heartbeat provides some of the sensation we describe as fear, for example. Facial feedback has often been cited as evidence for this theory, but some recent experiments have called it into question.

Before completing this project, Coles considered himself a fence-sitter on the issue. There had been seminal facial feedback research suggesting that participants found Gary Larson’s The Far Side comics funnier when they held a pen or pencil in their teeth without letting their lips touch it (supposedly activating the same muscles as a smile). But in 2016, 17 different labs tried and failed to replicate these results, casting the hypothesis into doubt.

When Coles conducted a meta-analysis of previous studies on the subject in 2019, which included a variety of different methods, his results seemed to indicate there was at least some evidence supporting facial feedback. So he decided to try to settle the matter in a way that would convince both skeptics and believers. He organized the Many Smiles Collaboration, a group that included people on both sides of the issue as well as fence-sitters like Coles, and together they devised a methodology that everyone was satisfied with.

“Rather than quibble and debate over Twitter and through journal articles, which would take decades and probably not be that productive, we said, ‘Let’s just come together and design something that would please both sides,’ ” Coles said. “Let’s figure out a way that we could potentially convince proponents that the effect isn’t real, and potentially convince critics that the effect is real.”

The researchers created a plan that included three well-known techniques intended to encourage participants to activate their smile muscles. One-third of participants were directed to use the pen-in-mouth method, one-third were asked to mimic the facial expressions seen in photos of smiling actors, and the final third were given instructions to move the corners of their lips toward their ears and lift their cheeks using only the muscles in their face.

In each group, half the participants performed the task while looking at cheerful images of puppies, kittens, flowers, and fireworks, and the other half simply saw a blank screen. They also saw these same types of images (or lack thereof) while directed to use a neutral facial expression.

In order to disguise the goal of the trial, the researchers mixed in several other small physical tasks and asked participants to solve simple math problems. After each task, participants rated how happy they were feeling.

The Many Smiles Collaboration collected data from 3,878 participants from 19 countries. After analyzing their data, the researchers found a noticeable increase in happiness from participants mimicking smiling photographs or pulling their mouth toward their ears. But much like the 2016 group, they didn’t find a strong mood change in participants using the pen-in-mouth technique.

“The effect wasn’t as reliable with the pen-in-mouth condition,” Coles said. “We’re not sure why. Going into the study, we assumed that all three techniques created the correct muscular configuration for an expression of happiness. But we found some evidence that the pen-in-mouth condition may not be actually creating an expression that closely resembles smiling.”

For instance, the act of holding the pen may require some amount of teeth-clenching that isn’t usually present in a genuine smile, which could be a confounding factor. Nonetheless, the evidence from the other two techniques is clear and provides a compelling argument that human emotions are somehow linked to muscle movements or other physical sensations.

“The stretch of a smile can make people feel happy and the furrowed brow can make people feel angry; thus, the conscious experience of emotion must be at least partially based on bodily sensations,” Coles said. “Over the past few years, the science took one step back and a few steps forward. But now we’re closer than ever to understanding a fundamental part of the human condition: emotion.”

Coles is a research scientist at Stanford University, the co-director of the Stanford Big Team Science Lab , and the director of the Psychological Science Accelerator . He conducts research on emotion, cross-cultural psychology, and models of scientific collaboration.

To read all stories about Stanford science, subscribe to the biweekly  Stanford Science Digest .

How Smiles Control Us All

And why we're terrible at faking them

The neuronal signals for smiles usually start in the cortex of our brain. From there they travel to the deeper part, the brainstem -- which, in terms of evolution, also happens to be one of the oldest parts of our brain. From there, a nerve that's large enough to be visible to the naked eye, called the seventh cranial nerve, carries the signal in front of the ear to the more central part of the face, where it reaches the smile muscle.

The smile muscle is attached from the mouth to the cheekbone. When this nerve fires, the muscle is activated, the corners of our mouth are pulled up, and we look happy. And if it is a true smile, one that signifies real enjoyment by its wearer, then a branch of the facial nerve also activates little muscles around the eyes,  leading to wrinkling around the eyes in addition to a mouth smile.

The scientific analysis of the smile really began with the French anatomist Guillaume-Benjamin-Amand Duchenne de Boulogne. In the 1860s, he used electrical currents to make his subjects' "facial muscles contract to speak the language of the emotions and the sentiments." Duchenne believed that one could gain insight into the ways the face expresses emotions by studying the muscles underlying facial movement. He recorded the expressions produced by the electrical stimulation by taking photographs and was the first to use photography to prove a scientific theory. Duchenne showed that in the particular smile he called the "smile of joy," the muscle that is just to the side of the eyes (called orbicularis oculi) is activated. When this muscle contracts, it creates creases, sometimes called crow's feet. He called this the "true smile," the pure smile of enjoyment. Duchenne concluded that the mouth smile obeys the will, but the eye smile does not. He said, "The muscle around the eye ... is only brought into play by a true feeling, an agreeable emotion. Its inertia in smiling unmasks a false friend."

In the image at right, Duchenne applies electrodes to his cooperative subject in order to stimulate the contraction of the smile muscle (zygomaticus major) that pulls the corners of the mouth up when we smile. His subject is clearly enjoying this. Duchenne's jolt of electricity activates the smile muscle around the mouth, but the gentleman's eyes are also smiling, as seen by the creases formed just to the side of his eyes so the happiness comes from inside. When Duchenne first applied the electricity, only the  smile muscle around the mouth was activated; he realized that it didn't look like a true, natural smile, so he told this gentleman a joke to make his eyes smile as well.

Paul Ekman, who led the scientific investigation of facial expressions in the twentieth century, has shown that Duchenne was right. Few of us can fake an eye smile. If you're sitting across from a new business associate and he smiles at you but you're still not sure if you should sign off on a new business venture, look at those little lines around the outside of his eyes. If they wrinkle up like crow's feet, then his smile is a real signifier of pleasure or happiness. The absence of smiling eyes should alert you that your new associate's smile is not necessarily as friendly as it looks.

A century after Duchenne recorded his remarkable experiments, Dr. Paul Ekman honored the anatomist by terming the smile involving the eyes the "Duchenne smile." Ekman found that the failure to distinguish between different types of smiles showed up in much scientific research over the years and might explain contradictory findings regarding the universal meaning of the smile. Other scientists confirmed their findings and found that the Duchenne smile appears significantly more often when people are freely enjoying themselves than in situations that would require feigned smiles. The eyes do not lie unless, of course, the person has received Botox around the eyes, in which case the skin around the eyes is unable to wrinkle up, no matter how true a smile.

Certainly what we see greatly influences when we smile, but it is not necessary. We need no visual feedback to smile. Darwin discovered that those who are born blind will still smile appropriately during a conversation. You can smile when all alone, but smiling is definitely enhanced by socializing; it happens six times more frequently in social settings.

Some of the complexities of smiling can be appreciated by examining those who can't do it normally. People who have suffered brain damage may not be able to smile when asked to but will still involuntarily smile at a joke. Conversely, patients suffering from Parkinson's disease, a disease of dopamine-containing neurons in the brain, may be able to turn up the corners of the mouth when asked to smile but after getting a joke may lack the ability to smile as a natural, automatic response. Patients who have had a stroke leading to paralysis of half of their face lack an ability to voluntarily move one side of their face. They show a crooked smile when asked to grin but a normal smile on hearing a joke, indicating intact nerve pathways beyond their conscious control. Clearly, the pathways for smiling are quite elaborate, with both unconscious and conscious connections that receive inputs from different parts of the brain.

One wonders whether it is only a coincidence that those of us who socialize the most tend to get less depressed. We have seen how socializing is a great activator of smiling -- perhaps smiling is doing more than we think. Do children suffer less often from depression because they spend more time playing and smiling? It is so easy to forget that your face is always speaking to you: 24/7, your brain is keeping track of how many smiles you created with your face. Your smile scorecard is not something you are consciously aware of, but your unconscious has intimate knowledge of it.

I believe that smiling more benefits you directly -- even without its social benefits. You go to the gym to strengthen your muscles. Why not go to the smiling gym to strengthen your positive emotions?

One study found that women who had smiled the most in their college yearbook photos had happier lives, happier marriages, and fewer personal setbacks in the following 30 years.  Another study finds a correlation between how big a smile you made for a baseball card photo and how long you will live. Those baseball players who had the broadest smiles lived, on average, seven years longer than those who smiled the least.

How could smiling lead to happier marriages and longer lives? The key is probably the reduction of stress that your body and mind feel. Smiling helps generate positive happy emotions within you, and this leads to a decrease in the stress-induced hormones that negatively affect your physical and mental health. Now, of course, there is only a correlation between smiling and a happy life -- it certainly doesn't prove that smiling will make your marriage better or lengthen your life. Perhaps those who smiled most were just innately happier people or smiled more because life was already treating them well in college, predicting more good things to come. Studies such as these can't  show what causes what. Waves are correlated with beaches, but do beaches cause waves or waves bring beaches?

But if one assumes that those who smile more will be happier, what happens to those who smile less? Shouldn't those who developed difficulty smiling as adults suffer more from depression, all other things being equal? Nature has done the experiment if one knows where to look. To probe for cause and effect, doctors studied what happened to patients who, because of facial nerve damage, were unable to move their faces normally. The facial nerve is commonly damaged in adult life by a condition known as Bell's palsy. There are three major parts of the facial nerve, so it is possible to lose the ability to frown but be able to smile, or vice versa. These researchers asked their patients to raise their eyebrows, squint, smile, and pucker their mouths to assess the extent of their facial disability. Their hypothesis was that the inability to smile would increase one's risk of depression.

Recommended

The results showed that a general impairment in moving one's face was not associated with depression. However, patients who specifically lacked the ability to smile were much more likely to become depressed, and their depression was more severe. There are several possible explanations. First, smiling occurs in social situations and helps facilitate positive emotions and relationships with others. Those individuals who find themselves unable to smile may experience more social isolation, leading to more depressive symptoms from loneliness. This could be a strong negative feedback loop. Second, smiling, by activation of the smile muscle, would initiate a feedback loop to the brain, activating our happy part of the brain, contributing to a more positive mood and more smiling. Those with impaired smiling would have the positive feedback interrupted and more consistent weight on the side of depression. I believe the second explanation is more important, but there is no evidence to help us decide.

This post is excerpted from  The Face of Emotion .

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Introduction.

• < Previous

What’s in a smile? A review of the benefits of the clinician’s smile

• Article contents
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Andrew James Beamish, Jessica Jane Foster, Harry Edwards, Torsten Olbers, What’s in a smile? A review of the benefits of the clinician’s smile, Postgraduate Medical Journal , Volume 95, Issue 1120, February 2019, Pages 91–95, https://doi.org/10.1136/postgradmedj-2018-136286

• Permissions Icon Permissions

For millennia, the smile has been recognised as a powerful communication device, offering benefits to both giver and receiver with few drawbacks. A sign of compassion, empathy and friendliness, smiling can benefit healthcare professionals and their patients, helping to build a relationship of trust. But beware the false smile, which is all too easily identified and may do more harm than good. In this review, we explore the literature surrounding smiling in healthcare and beyond, discussing the many reasons to be cheerful, from good health to a happy marriage, among aviators, table waiters, doctors, dentists and even dogs.

For millennia, the smile has been recognised as an incredibly powerful communicative device. The Book of Proverbs tells us that ‘smiling faces make you happy ’ (Proverbs 15:30), and the Islamic prophet Muhammad taught that ‘meeting your brother with a smile… is Sadaqah (an act of generous compassion) ’ (Book 1, Hadith 121).

In the latter part of the 19th century Charles Darwin ( figure 1 ) explored the nature of smiling in his book, ‘The expression of the emotions’. 1 Famed for his famous observation of various species, Darwin described the smile as a common facial mechanism for communicating happiness or joy. He agreed with the observation of the renowned French Neurologist, Guillaume Duchenne, 2 ( figure 2 ) that, while smiling involves ‘ the combined contraction of the zygomatic major muscle, and the orbicularis oculi…’ ( figure 3 ) ‘the first obeys the will, but the second is only put in play by the sweet emotions of the soul’ (p 126). That is to say that the genuine smile is hard to replicate without a truly joyful stimulus. This Duchenne smile is what we generally consider to be a ‘genuine’ smile and smiling without contraction of the orbicularis oculi muscle is often perceived as ‘fake’, also known as non-Duchenne or deliberate smiling.

Charles Darwin (author: Julia Margaret Cameron; Reprinted in Charles Darwin: His Life Told in an Autobiographical Chapter, and in a Selected Series of His Published Letters, edited by Francis Darwin. London:John Murray, Albemarle Street. 1892. Scanned by User: Davepape; public domain: https://commons.wikimedia.org/w/index.php?curid=3560761 ).

Guillaume-Benjamin Duchenne (de Boulogne) (author: G._Duchenne.jpg: unknown/anonymousderivative work: PawełMM (talk)-G._Duchenne.jpg; public domain: https://commons.wikimedia.org/w/index.php?curid=9701531 ).

Muscles of the smile. Both zygomaticus major and orbicularis oris are activated in the genuine ‘Duchenne’ smile, while only zygomaticus major is activated in a voluntary, or forced, smile (author: Sobotta, colour changed by was_a_bee. File: Sobo_1909_260.png; public domain: https://commons.wikimedia.org/w/index.php?curid=30438326 ).

In 1980, John Ohala hypothesised that the smile was borne of an acoustic origin, suggesting it began as a mechanism to sound more infantile, thus inviting caring, parental sentiments and appeasing potential aggressors. 3 He contrasted this with the hostile pouting extension of the lips, as displayed in the temper tantrum of a toddler, which could lower the vocal resonance to enhance the impression that the sound-maker was very large. 3

Many modern day scientists have since studied the smile, their reasons ranging from chasing consumer cash, 4   5 or distinguishing desirable dentition, 6 to subconsciously stimulating Samaritans, 7 and the scientific study of psychology. 8 Never, however, has an author explored the myriad of benefits that the humble smile might afford the 21st century health professional.

Benefits to patients

A smile can represent a social reward to the perceiver, stimulating the brain’s reward system via the basal ganglia, prefrontal cortex and, to a lesser degree, the amygdala. 9 Functional MRI studies have shown the dopamine-associated reward-processing regions of a mother’s brain lighting up impressively in response to a simple smile from her infant. 10 We recognise a smile at twice the distance of other facial expressions 11 and, once we do, it is typical for the perceiver to automatically mimic the expression, usually within half a second. 12 In fact, it has been shown that automatic reciprocation of the smile, measured as activation of smiling muscles, such as zygomaticus major ( figure 3 ), begins so quickly that, not only do we have no choice about whether to return a smile, but it is almost impossible to avoid doing so. 13 This does not occur universally and the more empathic a person is, the greater the response that can be expected. 14 However, when mimicry of a smile does occur, it appears to be associated with a corresponding emotion of happiness, conscious or unconscious, 14 an effect referred to as emotional contagion. 9 So when we smile at our patients, there is a very good chance that they will be entirely unable to avoid feeling a little better, whether or not they return the smile.

A monetary value has even been placed on the smile, in a study using functional MRI to compare observing smiling faces with other pleasurable stimuli. 15 Incredibly, this study reportedly found that a single smiling face had the potential to induce pleasure equivalent to being given up to £16 000 in cash, or eating 2000 chocolate bars. 15 Smiling was deemed to offer a better short-term high than sexual intercourse, shopping or listening to your favourite song. However, with original data in short supply, this report’s findings are somewhat isolated and should be taken with caution. It is also worth noting that a frown can induce an opposite response through emotional contagion and is, therefore, well worthwhile avoiding. 14

Smiling for your patients may help them to remember what you are discussing with them or at least who you are. The smile’s potent reward properties have been shown to promote effective memory via functional connectivity between the orbitofrontal cortex and hippocampus, enabling subjects to remember the names of smiling faces more readily than neutral faces. 16

Brief non-verbal interactions, such as a wave, can offer a vast amount of important clinical information in little more than a split second 17 and it is likely that the response to a smile can achieve the same. It has been suggested that smiling helps clinicians build a rapport with patients, helps ease patients ’ anxieties and instills feelings of trust towards the clinician. 18 Such experiences are backed up by evidence from nursing, where patients reported greater confidence in their nurse’s skill level when they seemed to be happy and smiling. 19 Indeed, psychologists have shown that we are more likely to trust a person who smiles, than someone who does not. 20

The emotional burden of illness is borne by relatives and friends, as well as patients. A smile from a loved one, inspired by yours, may even continue the chain of emotional contagion far outside the hospital walls.

Benefits to the smiler

Beyond the benefits to the recipient, the benefits to the smiler are numerous, even when the smile is voluntary rather than spontaneous. Researchers have demonstrated that voluntary smiling, or faking a smile, can produce similar electrical brain activity to spontaneous, or genuine, smiling. 21 This appears to result from the activation of feedback pathways from muscles of facial expression to the brain, physiologically triggering happy emotions. 22 So offering a voluntary smile may well spark your emotions sufficiently to turn it into the genuine article. Should you experience this effect, rejoice and be happy; for it has been shown that improving our own state of happiness, or affect, has a positive effect on our willingness to help others, and indeed the pleasure we derive from doing so. 23 Perhaps, therefore, giving that smile might even make you want to serve your patients better, as well as making you feel happier.

Examining a broad range of evidence, Diener and Chan concluded that happy people live longer and enjoy better health, 24 and others have shown happiness to be protective against both coronary heart disease 25 and chronic health conditions, 26 although such benefits are disputed. 27   28 In addition to potential benefits to your health, and with the prospect of a long life ahead, you will be pleased to discover that smiling could also be the key to a long and happy marriage. Herstenstein and colleagues examined photographs from childhood and young adulthood and found that people who were observed to smile more intensely were less likely to divorce later in life. 29 However, do bear in mind that specific studies of smiling and its relation to health and marriage are limited in number, examine snapshots in time, such as school photographs, and show inconsistent findings. 30   31

Benefits to the team

As a team member, your smile may well also be beneficial to colleagues. A study in the early part of this century showed that smiling can activate a positive mood, promoting altruistic behaviour. 7 When individuals were smiled at, they were significantly more likely to offer help to a stranger who had dropped some items shortly afterward. 7 In a similar way, waitresses have been shown able to boost their tips by smiling to customers, both male and female, 32 and motorists were much more likely to stop for female hitchhikers if they smiled, although there was no such luck for men seeking a free ride. 33 Perhaps a culture of smiling may encourage effective team working, with colleagues more willing to lend a hand when things get busy or difficult.

Another study, examining team working directly, showed that members of a team drew inferences regarding their performance from the emotions of their leader. When feedback was delivered with a smile and an upbeat tone, workers felt that they had performed well, while the converse was true when the same feedback was delivered with a frown and an irritable tone. 8 A smile may add weight to one’s positive feedback to a well-performing team, while withholding a smile may undermine the same verbal feedback. Sadly, evidence to inform hospital managers whether to frown or smile when quoting our performance against targets remains scarce in the literature.

In the business sector, the phrase ‘service with a smile’ is so commonly encountered as to have become a cliché. It has been shown that positive displays of emotion can enhance customer attitudes towards an organisation leading to positive customer evaluations of the quality of service provided. 5 As a service industry, it follows that such findings may be translated to the healthcare setting. However, it appears that enforcing smiling, as a requirement of employment, would likely be unwise. A meta-analysis of almost a hundred studies in the service industry concluded that emotionally discordant behaviours, such as forcing a smile for customers, detrimentally affects not only the performance of staff members, but also their well-being. 4 It seems that creating a working environment and conditions that promote high morale and happy workers would be far more beneficial than telling staff members to smile.

Delivering the perfect smile

We ought to pay attention to how we deliver our smiles too. For those interested in the science of the perfect smile, Charles Hulsey suggests that aesthetically desirable factors include: symmetry, a good ‘smile line ratio’ (harmony between the arcs of the teeth and the lips), an upper lip rise to the top of the middle teeth, and corners of the mouth higher than the midline height. 6

It is important to bear the recipient of your smile in mind, and ethnicity and gender appear to notably influence perceptions. A small multinational study reported significantly different lip preferences between Japanese, Hispanic American, African and European American lay persons. The Japanese preferred the least protrusive lip profiles and European Americans favoured the most protrusive. 34 Another study demonstrated the existence of some difficulty in cross-cultural interpretation of the smiling face. A narrow-lipped smile may be better received in Japan and a more open-lipped smile more effective in encounters with European Americans. 35

Showing genuine sympathy or empathy as a clinician is an efficient method of conveying helpful information to the patient, which can positively influence their emotions and behaviour. 36 However, beware the potential of the false smile to demolish any semblance of a valuable patient–clinician rapport. Even in 1873, Darwin observed the ease with which people were able to identify a false smile. He described more than 85% (21/24) of individuals recognising the false nature of a smile in a photograph; the remainder unable to decipher the expression. 1 Ekman and Friesen described how true emotions can ‘leak’ out when we attempt to disguise them, as we are far less adept at controlling facial and bodily expressions than we are at choosing our words. 37 A patient could potentially interpret a false smile, or a mismatch between affect and words, as condescension, sarcasm, disinterest, inappropriate humour, lack of empathy, 38 or even an unwanted advance. It follows that advising people to smile could well lead to a counterproductive false smile, paradoxically leading to sadness or upset in the patient, even further reducing the genuine incentive for either party to smile spontaneously. It has been shown that a more intense smile is associated with a greater likelihood of interpretation as genuine. 39

However, following decades of acceptance that the Duchenne smile was entirely involuntary and extremely difficult to voluntarily replicate, evidence challenging this assumption has emerged. 39 Gunnery and colleagues 39 showed that, not only is it possible to deliver a deliberate Duchenne smile, even if positive affect is not being felt, but that a ‘non-trivial number’ of individuals seems to be able to achieve it. Unfortunately, while learning to better deliver a Duchenne smile could be considered a potential avenue for improvement, recent thinking suggests that this is actually an inherited ‘trait’ rather than a learnt skill. 39

Among up to 50 described types of smile, 40 some are recognised as a response to stressful stimuli, often arising from uncomfortable feelings such as embarrassment, self-consciousness, disgust or distress and often interpreted as amusement rather than distress. 41

It is also important to note that the distressed smiler is perceived to be less socially appropriate and less likeable than the person who offers no smile at all. 41 Offering no smile at all seems more likely among men as there is almost unanimity that women smile more than men, a phenomenon largely dependent on culture, age and role. 42 Perhaps, there is more room for increasing smile frequency among the male contingent. However, much progress has been made since the days of gender-stereotyped suggestions in the literature that a flight attendant ought to ‘really work on her smiles’ and ‘manage her heart’ to create a smile that seems ‘spontaneous and sincere’. 43

Finally, if you find that your smile has been less than convincing in the workplace, seek solace when you return home to Rex, by shooting a smirk to ‘man’s best friend’. Recent research suggests your dog probably recognises the smile on your face, 44 which might just rekindle a genuine smile after a long hard day.

While it is unlikely that forcing a smile every day will prolong your marriage or prevent disease and death, a heartfelt smile is associated with numerous benefits, whether given or received. On the contrary, smiling’s drawbacks are few. What’s more, there is a real chance that conveying a sense of positivity to patients has the potential to brighten up their day, even just a little. And why not extend the benefits to colleagues and perhaps even yourself? Whether a smile is worth a penny or £16,000, to you, reader, this one is free ☺.

Smiling has potential benefits for the smiler, recipient and wider team.

Smiling can promote improved mood, memory and trust.

The reflexive positive response to receiving a smile is almost impossible to avoid.

Does smiling have potential benefits to the smiler?

Does smiling have potential benefits for the recipient?

Does smiling have potential benefits for the wider team?

Darwin C. The expression of the emotions in man and animals . London: John Murray, 1873.

Strathearn L, Li J, Fonagy P, et al . What’s in a smile?Maternal brain responses to infant facial cues. Pediatrics 2008;122:40-51.

Liu B, Floud S, Pirie K, et al . Does happiness itself directly affect mortality? The prospective UK Million Women Study. Lancet 2016;387:874-81.

Nabi H, Kivimaki M, De Vogli R, et al . Positive and negative affect and risk of coronary heart disease: Whitehall II prospective cohort study. BMJ 2008;337:a118

Ekman P and Friesen WV. Nonverbal leakage and clues to deception. Psychiatry 1969;32:88-106.

French Neurologist, Guillaume Duchenne, described smiling as involving ‘the combined contraction of the zygomatic oculi, and the orbicularis major’ muscles.

It is hypothesised that the smile was borne as a mechanism to lower the vocal resonance to enhance the impression that the sound-maker was very large.

It has been shown that automatic reciprocation of the smile is almost impossible to avoid.

Voluntary (or forced) smiling can initiate the same emotions as genuine smiling.

Smiling undermines patients’ confidence in their caregiver’s skill level.

False — Duchenne described ‘the combined contraction of the zygomatic major muscle, and the orbicularis oculi’. 2

False — John Ohala hypothesised that the smile was borne of an acoustic origin, suggesting it began as a mechanism to sound more infantile, thus inviting caring, parental sentiments and appeasing potential aggressors. 3

True — Dimberg and colleagues showed that automatic reciprocation of the smile, measured as activation of smiling muscles, begins so quickly that it is almost impossible to avoid. 13

True — Researchers have demonstrated that voluntary smiling, or faking a smile, can produce similar electrical brain activity to spontaneous, or genuine, smiling. 21 This appears to result from the activation of feedback pathways from muscles of facial expression to the brain, physiologically triggering happy emotions. 22

False — Patients reported greater confidence in their nurse’s skill level when they seemed to be happy and smiling. 19

AJB conceived the project. All authors searched the literatureand contributed to the acquisition of data, interpreted the data acquired and together drafted the manuscript. All authors approved the final version and are accountable for its content.

The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

None declared.

Not required.

Not commissioned; internally peer reviewed.

Darwin   C . The expression of the emotions in man and animals . London : John Murray , 1873 .

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New Study Suggests Smiling Influences How You See the World

Can a smile trick your mind into a more positive mood.

Posted August 14, 2020 | Reviewed by Jessica Schrader

“Smile and the world smiles with you, cry and you cry alone,” goes the song. For decades, singers have crooned about the power of smiling to make you feel better. With the pandemic and increases of anxiety and depression , smiling and optimism don’t come easily these days. But a new study to be published in the journal Experimental Psychology suggests the sheer activity of moving your facial muscles to form a smile—even if you fake it—can influence our perception of emotions. Could smiling be a simple antidote to help us get through these extraordinary times?

Clinicians and Twelve Step programs have batted around the age-old strategy of “acting as if”—a simple, yet powerful tool that says you can lift your mood by acting as if you already feel better than you actually do.

Here’s how it works. You give yourself to a certain performance as if it’s how you already feel. When you act "as if," the mood you pretend becomes a reality. Suppose you’re angry toward someone who offended you but you want to be forgiving . You can start to feel forgiving by acting as if you are forgiving. Perhaps you’re feeling envious of a friend’s good news but want to be happy for him or her. You can be happy by acting as if you are happy.

Science-Backed Evidence for “Acting As If”

It might sound too simple to be true, but science backs it up. A previous study at the University of Rochester found that when faced with a difficult task, people who sat up straight and crossed their arms persevered for almost twice as long as the others. Changing body posture, breathing patterns, muscle tension, facial expressions, gestures, movements, words, and vocal tonality releases chemicals that can change our internal state. Standing tall with shoulders back makes us look confident, plus it makes us feel more confident. Training the body to position itself the way you want to think and feel about yourself adjusts your thoughts and feelings to the way you want them to be. Making body adjustments—pulling your shoulders back, standing or sitting up straight, walking in a more expansive way—can pull you out of self-doubt, disappointment, or dread and any other self-defeating emotion .

The reason it works is because of the mind-body connection. When you “act as if,” the rest of you follows suit. The cells of your body constantly eavesdrop on your thoughts from the wings of your mind. When you’re doubtful or disappointed about something, your body goes with the downturn of your feelings and dumps a cocktail of neuropeptides into your bloodstream, making you feel worse in a matter of seconds. As you focus on the negative feeling, you might not even realize that you hunch your head or slump when you walk. This body posture not only reflects how you feel but also contributes to how you feel, which makes you feel even worse and come across in a negative way.

The same seems to be true with smiling. An earlier study by Michael Lewis and his research team at the University of Cardiff in Wales found that people who received cosmetic Botox injections (compromising their ability to frown) reported being happier than did people who could frown normally. The researchers administered an anxiety and depression questionnaire to 25 females, half of whom had received frown-inhibiting Botox injections. The Botox recipients reported feeling happier and less anxious in general; more important, they did not report feeling any more attractive, which suggests that the emotional effects were not driven by a psychological boost that could come from the treatment’s cosmetic nature.

The New Study

Research from the University of South Australia provides evidence that the act of smiling can trick your mind into happiness , simply by how you move your facial muscles. We may feel bad not just because facial expressions reflect how we feel, but because they contribute to how we feel.

The new study evaluated the impact of a covert smile on perceptions of both face and body expressions. In both cases, a smile was induced by participants holding a pen between their teeth, forcing their facial muscles to replicate the movement of a smile. Participants in one group held a pen between their teeth, forcing their facial muscles into a smile while a comparison group held no pen between their teeth. Both groups were shown a range of facial expressions (from frowns to smiles) and a series of body movements (from “sad walking” videos to “happy walking” videos).

Under the “pen-in-the-teeth” condition, those who adopted the forced “smiling” facial position were more inclined to interpret the facial expressions of others as positive, compared to the “no-pen” group, which replicated a 10-year old study. The second part of the study, which hasn't been documented before now, showed similar results for how body movements are perceived: Participants in the "pen-in-mouth" group were more likely to perceive body movements of others as happier than the control group.

“When your muscles say you’re happy, you’re more likely to see the world around you in a positive way,” the chief investigator, Dr. Fernando Marmolejo-Ramos, said in a news release . He concludes that "If we can trick the brain into perceiving stimuli as 'happy,' then we can potentially use this mechanism to help boost mental health.”

Smile Whether You Mean It or Not

This study contributes to the scientific backing of the old adage, “fake it, ‘til you make it.” Of course, you don’t want to walk around with a pen between your teeth. But because our perceptual and motor systems are intertwined, your facial muscular activity alters how you perceive the facial and body expressions of others. Simply activating a smile contributes to a positive neurological reaction. In other words, when your facial muscles say you’re happy, you’re more likely to experience the world in a more positive light.

So next time you’re feeling blue or have a sour attitude, jump start a feel-good day by putting on a happy face and smiling. Remind yourself that frowning and dreading make you feel worse. Even if you have to fake it to start, convince yourself that facing the day is a piece of cake, act as if it’s true, and then notice how it becomes true.

Friedman, R. & Elliot, A. J. (2007). The effect of arm crossing on persistence and performance. European Journal of Social Psychology, 38 (3), 449-461. DOI.org/10.1002/ejsp.444

Lewis, M. B., et al. (2009). Botulinum toxin cosmetic therapy correlates with a more positive mood. Journal of Cosmetic Dermatology , 8, 24-26.

Marmolejo-Ramos, F., Murata, A., Sasaki, K., Yamada, Y., Ikeda, A., Hinojosa, J. A., Watanabe, K., Parzuchowski, M., Tirado, C., & Ospina, R. (2020). Your face and moves seem happier when I smile. Facial action influences the perception of emotional faces and biological motion stimuli. Experimental Psychology, 67 (1), 14-22.

Bryan Robinson, Ph.D. , is a Professor Emeritus at the University of North Carolina at Charlotte. He is the author of more than 37 books.

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