The facial feedback hypothesis, rooted in the conjectures of Charles Darwin and William James, is that one's facial expression directly affects their emotional experience. Specifically, physiological activation of the facial regions associated with certain emotions holds a direct effect on the elicitation of such emotional states, and the lack of or inhibition of facial activation will result in the suppression (or absence altogether) of corresponding emotional states.[1]
Variations of the facial feedback hypothesis differ in regards to what extent of engaging in a given facial expression plays in the modulation of affective experience. Particularly, a "strong" version (facial feedback is the decisive factor in whether emotional perception occurs or not) and a "weak" version (facial expression plays a limited role in influencing affect). While a plethora of research exists on the facial feedback hypothesis and its variations, only the weak version has received substantial support, thus it is widely suggested that facial expression likely holds a minor facilitative impact on emotional experience. However, a 2019 meta-analysis, which generally confirmed small but significant effects, found larger effect sizes in the absence of emotional stimuli, suggesting that facial feedback has a stronger initiating effect rather than a modulating one.[2]
Further evidence showed that facial feedback is not essential to the onset of affective states.[3] This is reflected in studies investigating emotional experience in facial paralysis patients when compared to participants without the condition. Results of these studies commonly found that emotional experiences did not significantly differ in the unavoidable absence of facial expression within facial paralysis patients.[4]
Charles Darwin was among the first to suggest that physiological changes caused by an emotion had a direct impact on, rather than being just the consequence of that emotion. He wrote:
The free expression by outward signs of an emotion intensifies it. On the other hand, the repression, as far as this is possible, of all outward signs softens our emotions... Even the simulation of an emotion tends to arouse it in our minds.[5]:366
Succeeding this postulation, William James (who was also a principal contributor to the related James-Lange theory) proposed that instead of the common belief an emotional state results in muscular expression, proprioception activated by a stimulus "is the emotion".[6]:449 and should one "refuse to express a passion...it dies".[6]:463 In other words, in the absence of awareness of bodily movement, there is only intellectual thought, with consequently the mind being devoid of emotional warmth.
During this period, the posits culminating in the facial feedback hypothesis lacked evidence, apart from limited research in animal behavior and studies of people with severely impaired emotional functioning. Formalized research on Darwin's and James' proposals were not commonly conducted until the latter half of the 1970s and the 1980s; almost a century after Darwin's first proposal on the topic.[7][8] Furthermore, the term "facial feedback hypothesis" was not popularized in research until around 1980, with one early definition of the hypothesis being "skeletal muscle feedback from facial expressions plays a causal role in regulating emotional experience and behaviour."[9]
Development of the theory
While James included the influence of all bodily changes on the creation of an emotion, "including among them visceral, muscular, and cutaneous effects",[10]:252 modern research mainly focuses on the effects of facial muscular activity. One of the first to do so, Silvan Tomkins wrote in 1962 that "the face expresses affect, both to others and the self, via feedback, which is more rapid and more complex than any stimulation of which the slower moving visceral organs are capable".[10]:255
Two versions of the facial feedback hypothesis came to be commonly referenced, albeit sometimes being unclear in distinction.[11]
The weak version, rooted in Darwin's writings, proposes that facial expression modulates emotional states in a minor and limited manner. Thomas McCanne and Judith Anderson (1987)[12] instructed participants imagine pleasant or unpleasant imagery while they increased or suppressed activity with certain facial muscle regions responsible for the actions of smiling or frowning: respectively the zygomatic and corrugator muscle regions. A subsequent change in participants' emotional response was implied to have occurred as a result of intentional manipulation of the aforementioned facial muscle regions.
The strong variation—coinciding with James' postulations—implies that facial feedback is independently and chiefly responsible for the onset and perception of an emotional state.[3]
Since the writings of Darwin and James, extensive research on the facial feedback hypothesis has been conducted, with multiple studies being largely formative to how the facial feedback hypothesis is defined, tested, and accepted, with some of the most notable studies conducted in the 1970s and 1980s—a period of time that was critical to the contemporary development of the facial feedback hypothesis. For example, arguably one of the most—if not the most—influential studies on the facial feedback hypothesis was conducted by Fritz Strack, Leonard L. Martin, and Sabine Stepper in 1988. Strack, Martin, and Stepper pioneered a technique in which researchers were able to measure the effect of the actions of smiling and frowning on affect through inducing such expressions in an undetectable manner to the participant, offering a supposed level of control not yet before utilized in similar studies. This was achieved by asking each participant to hold a pen in between their teeth (inducing a smile) or between their lips (inducing a frown) while instructed to view comedic cartoons. The study concluded that participants who engaged in a smiling expression (pen between teeth) reported a higher humor response to the cartoons as opposed to when participants held a frowning expression (pen between lips).[13] This study proved to be highly influential in not only widespread acceptance of the facial feedback hypothesis (e.g., being commonly cited in introductory psychology classes), but also influenced numerous other ensuing studies to utilize elements from the 1988 procedure.[14]
In 2016, a large-scale Registered Replication Report was conducted with the purpose of meticulously replicating Strack, Martin, and Stepper's study and testing the facial feedback hypothesis across 17 different labs across varying countries and cultures. However, this study failed to reproduce the 1988 study's results, consequently failing to support the facial feedback hypothesis[15] and shedding doubt upon the validity of Strack, Martin, and Stepper's study.
Furthermore, Lanzetta et al. (1976) conducted an influential study[16] in support of the facial feedback hypothesis finding that participants who inhibited the display of pain-related expression had lower skin conductance response (a measure commonly used to measure the activation of the sympathetic nervous system, or stress response) and subjective ratings of pain, compared with participants who openly expressed intense pain.
However, in general, research of the facial feedback hypothesis is characterized by difficulty in determining how to measure the effect of facial expressions on affect without alerting the participant to the nature of the study and also ensure that the connection between facial activity and corresponding emotion is not implicit in the procedure.
Methodological issues
Originally, the facial feedback hypothesis studied the enhancing or suppressing effect of facial efference on emotion in the context of spontaneous, "real" emotions, using stimuli. This resulted in "the inability of research using spontaneous efference to separate correlation from causality".[10]:264 Laird (1974)[17] used a cover story (measuring muscular facial activity with electrodes) to induce particular facial muscles contraction in his participants without mentioning any emotional state. However, the higher funniness ratings of the cartoons obtained by those participants "tricked" into smiling may have been caused by their recognizing the muscular contraction and its corresponding emotion: the "self-perception mechanism", which Laird (1974) thought was at the root of the facial feedback phenomenon. Perceiving physiological changes, people "fill the blank" by feeling the corresponding emotion. In the original studies, Laird had to exclude 16% (Study 1) and 19% (Study 2) of the participants as they had become aware of the physical and emotional connection during the study.
Another difficulty is whether the process of manipulation of the facial muscles did not cause so much exertion and fatigue that those, partially or wholly, caused the physiological changes and subsequently the emotion. Finally, the presence of physiological change may have been induced or modified by cognitive process.
Experimental confirmation
Orbicularis oris muscle
In an attempt to provide a clear assessment of the theory that a purely physical facial change, involving only certain facial muscles, can result in an emotion, Strack, Martin, & Stepper (1988)[18] devised a cover story that would ensure the participants adopt the desired facial posing without being able to perceive either the corresponding emotion or the researchers' real motive. Told they were taking part in a study to determine the difficulty for people without the use of their hands or arms to accomplish certain tasks, participants held a pen in their mouth in one of two ways. The Lip position would contract the orbicularis oris muscle, resulting in a frown. The Teeth position would cause the zygomaticus major or the risorius muscle, resulting in a smile. The control group would hold the pen in their nondominant hand. All had to fill a questionnaire in that position and rate the difficulty involved. The last task, which was the real objective of the test, was the subjective rating of the funniness of a cartoon. The test differed from previous methods in that there were no emotional states to emulate, dissimulate or exaggerate.
As predicted, participants in the Teeth condition reported significantly higher amusement ratings than those in the Lips condition. The cover story and the procedure were found to be very successful at initiating the required contraction of the muscles without arising suspicion, 'cognitive interpretation of the facial action,[18] and avoiding significant demand and order effects. It has been suggested that more effort may be involved in holding a pen with the lips compared with the teeth.[11]
To avoid the possible effort problem, Zajonc, Murphy and Inglehart (1989) had subjects repeat different vowels, provoking smiles with "ah" sounds and frowns with "ooh" sounds for example, and again found a measurable effect of facial feedback.[11] Ritual chanting of smile vowels has been found to be more pleasant than chanting of frown vowels, which may explain their comparative prevalence in religious mantra traditions.[19]
However, doubts about the robustness of these findings was voiced in 2016 when a replication series of the original 1988 experiment coordinated by Eric-Jan Wagenmakers and conducted in 17 labs did not find systematic effects of facial feedback.[20] A subsequent analysis by Noah et al.[21] identified a discrepancy in method to the original 1988 experiment as a possible reason for the lack of systematic effect in the replication series.
Together, a number of methodological issues associated with the facial feedback hypothesis seem to be resolved in favor of Darwin's hypothesis. The moderate, yet significant effect of facial feedback on emotions opens the door to new research on the "multiple and nonmutually exclusive plausible mechanisms"[22] of the effects of bodily activity on emotions. A 2019 meta-analysis of 138 studies [23] confirmed small but robust effects.
Studies using botulinum toxin (botox)
Corrugator supercilii muscle
Because facial expressions involve both motor (efferent) and sensory (afferent) mechanisms, it is possible that effects attributed to facial feedback are due solely to feedback mechanisms, or feed-forward mechanisms, or some combination of both. Recently, strong experimental support for a facial feedback mechanism is provided through the use of botulinum toxin (commonly known as Botox) to temporarily paralyze facial muscles. Botox selectively blocks muscle feedback by blocking presynaptic acetylcholine receptors at the neuromuscular junction. Thus, while motor efference commands to the facial muscles remain intact, sensory afference from extrafusal muscle fibers, and possibly intrafusal muscle fibers, is diminished.
Several studies have examined the correlation of botox injections and emotion[24][25] and these suggest that the toxin could be used as a treatment for depression. Further studies have used experimental control to test the hypothesis that botox affects aspects of emotional processing. It has been suggested that the treatment of nasal muscles would reduce the ability of the person to form a disgust response which could offer a reduction of symptoms associated with obsessive compulsive disorder.[26]
In a functional neuroimaging study, Andreas Hennenlotter and colleagues[27] asked participants to perform a facial expression imitation task in an fMRI scanner before and two weeks after receiving botox injections in the corrugator supercilii muscle used in frowning. During imitation of angry facial expressions, botox decreased activation of brain regions implicated in emotional processing and emotional experience (namely, the amygdala and the brainstem), relative to activations before botox injection. These findings show that facial feedback modulates neural processing of emotional content, and that botox changes how the human brain responds to emotional situations.
In a study of cognitive processing of emotional content, David Havas and colleagues[28] asked participants to read emotional (angry, sad, happy) sentences before and two weeks after botox injections in the corrugator supercilii muscle used in frowning. Reading times for angry and sad sentences were longer after botox injection than before injection, while reading times for happy sentences were unchanged. This finding shows that facial muscle paralysis has a selective effect on processing of emotional content. It also demonstrates that cosmetic use of botox affects aspects of human cognition – namely, the understanding of language.
Autism spectrum disorders
A study by Mariëlle Stel, Claudia van den Heuvel, and Raymond C. Smeets[29] has shown that the facial feedback hypothesis does not hold for people with autism spectrum disorders (ASD); that is, "individuals with ASD do not experience feedback from activated facial expressions as controls do".
A smile is a facial expression formed primarily by flexing the muscles at the sides of the mouth. Some smiles include a contraction of the muscles at the corner of the eyes, an action known as a Duchenne smile. Among humans, a smile expresses delight, sociability, happiness, joy, or amusement. It is distinct from a similar but usually involuntary expression of anxiety known as a grimace. Although cross-cultural studies have shown that smiling is a means of communication throughout the world, there are large differences among different cultures, religions, and societies, with some using smiles to convey confusion, embarrassment or awkwardness.
A facial expression is one or more motions or positions of the muscles beneath the skin of the face. According to one set of controversial theories, these movements convey the emotional state of an individual to observers. Facial expressions are a form of nonverbal communication. They are a primary means of conveying social information between humans, but they also occur in most other mammals and some other animal species.
Self-perception theory (SPT) is an account of attitude formation developed by psychologist Daryl Bem. It asserts that people develop their attitudes by observing their own behavior and concluding what attitudes must have caused it. The theory is counterintuitive in nature, as the conventional wisdom is that attitudes determine behaviors. Furthermore, the theory suggests that people induce attitudes without accessing internal cognition and mood states. The person interprets their own overt behaviors rationally in the same way they attempt to explain others' behaviors.
Amusement is the state of experiencing humorous and entertaining events or situations while the person or animal actively maintains the experience, and is associated with enjoyment, happiness, laughter and pleasure. It is an emotion with positive valence and high physiological arousal.
Robert Bolesław Zajonc was a Polish-born American social psychologist who is known for his decades of work on a wide range of social and cognitive processes. One of his most important contributions to social psychology is the mere-exposure effect. Zajonc also conducted research in the areas of social facilitation, and theories of emotion, such as the affective neuroscience hypothesis. He also made contributions to comparative psychology. He argued that studying the social behavior of humans alongside the behavior of other species, is essential to our understanding of the general laws of social behavior. An example of his viewpoint is his work with cockroaches that demonstrated social facilitation, evidence that this phenomenon is displayed regardless of species. A Review of General Psychology survey, published in 2002, ranked Zajonc as the 35th most cited psychologist of the 20th century. He died of pancreatic cancer on December 3, 2008 in Palo Alto, California.
An emotional expression is a behavior that communicates an emotional state or attitude. It can be verbal or nonverbal, and can occur with or without self-awareness. Emotional expressions include facial movements like smiling or scowling, simple behaviors like crying, laughing, or saying "thank you," and more complex behaviors like writing a letter or giving a gift. Individuals have some conscious control of their emotional expressions; however, they need not have conscious awareness of their emotional or affective state in order to express emotion.
A frown is a facial expression in which the eyebrows are brought together, and the forehead is wrinkled, usually indicating displeasure, sadness or worry, or less often confusion or concentration. The appearance of a frown varies by culture. An alternative usage in North America is thought of as an expression of the mouth. In those cases when used iconically, as with an emoticon, it is entirely presented by the curve of the lips forming a down-open curve. The mouth expression is also commonly referred to in the colloquial English phrase, especially in the United States, to "turn that frown upside down" which indicates changing from sad to happy.
The negativity bias, also known as the negativity effect, is a cognitive bias that, even when of equal intensity, things of a more negative nature have a greater effect on one's psychological state and processes than neutral or positive things. In other words, something very positive will generally have less of an impact on a person's behavior and cognition than something equally emotional but negative. The negativity bias has been investigated within many different domains, including the formation of impressions and general evaluations; attention, learning, and memory; and decision-making and risk considerations.
Synkinesis is a neurological symptom in which a voluntary muscle movement causes the simultaneous involuntary contraction of other muscles. An example might be smiling inducing an involuntary contraction of the eye muscles, causing a person to squint when smiling. Facial and extraocular muscles are affected most often; in rare cases, a person's hands might perform mirror movements.
According to some theories, emotions are universal phenomena, albeit affected by culture. Emotions are "internal phenomena that can, but do not always, make themselves observable through expression and behavior". While some emotions are universal and are experienced in similar ways as a reaction to similar events across all cultures, other emotions show considerable cultural differences in their antecedent events, the way they are experienced, the reactions they provoke and the way they are perceived by the surrounding society. According to other theories, termed social constructionist, emotions are more deeply culturally influenced. The components of emotions are universal, but the patterns are social constructions. Some also theorize that culture is affected by the emotions of the people.
Discrete emotion theory is the claim that there is a small number of core emotions. For example, Silvan Tomkins concluded that there are nine basic affects which correspond with what we come to know as emotions: interest, enjoyment, surprise, distress, fear, anger, shame, dissmell and disgust. More recently, Carroll Izard at the University of Delaware factor analytically delineated 12 discrete emotions labeled: Interest, Joy, Surprise, Sadness, Anger, Disgust, Contempt, Self-Hostility, Fear, Shame, Shyness, and Guilt.
Determination is a positive emotional feeling that promotes persevering towards a difficult goal in spite of obstacles. Determination occurs prior to goal attainment and serves to motivate behavior that will help achieve one's goal.
Emotional responsivity is the ability to acknowledge an affective stimuli by exhibiting emotion. It is a sharp change of emotion according to a person's emotional state. Increased emotional responsivity refers to demonstrating more response to a stimulus. Reduced emotional responsivity refers to demonstrating less response to a stimulus. Any response exhibited after exposure to the stimulus, whether it is appropriate or not, would be considered as an emotional response. Although emotional responsivity applies to nonclinical populations, it is more typically associated with individuals with schizophrenia and autism.
Paula M. Niedenthal is a social psychologist currently working as a professor of psychology at the University of Wisconsin–Madison. She also completed her undergraduate studies at the University of Wisconsin at Madison where she received a Bachelor's in Psychology. She then received her Ph.D. at the University of Michigan before becoming a faculty member of the departments of Psychology at Johns Hopkins University and Indiana University. Until recently, she served as the Director of Research in the National Centre for Scientific Research at the Université Blaise Pascal in Clermont-Ferrand France. The majority of Niedenthal's research focuses on several levels of analysis of emotional processes, this would include emotion-cognition interaction and representational models of emotion. Niedenthal has authored more than 80 articles and chapters, and several books. Niedenthal is a fellow of the Society for Personality and Social Psychology.
The study of the evolution of emotions dates back to the 19th century. Evolution and natural selection has been applied to the study of human communication, mainly by Charles Darwin in his 1872 work, The Expression of the Emotions in Man and Animals. Darwin researched the expression of emotions in an effort to support his materialist theory of unguided evolution. He proposed that much like other traits found in animals, emotions apparently also evolved and were adapted over time. His work looked at not only facial expressions in animals and specifically humans, but attempted to point out parallels between behaviors in humans and other animals.
Facial electromyography (fEMG) refers to an electromyography (EMG) technique that measures muscle activity by detecting and amplifying the tiny electrical impulses that are generated by muscle fibers when they contract.
Non-verbal leakage is a form of non-verbal behavior that occurs when a person verbalizes one thing, but their body language indicates another, common forms of which include facial movements and hand-to-face gestures. The term "non-verbal leakage" got its origin in literature in 1968, leading to many subsequent studies on the topic throughout the 1970s, with related studies continuing today.
Emotion perception refers to the capacities and abilities of recognizing and identifying emotions in others, in addition to biological and physiological processes involved. Emotions are typically viewed as having three components: subjective experience, physical changes, and cognitive appraisal; emotion perception is the ability to make accurate decisions about another's subjective experience by interpreting their physical changes through sensory systems responsible for converting these observed changes into mental representations. The ability to perceive emotion is believed to be both innate and subject to environmental influence and is also a critical component in social interactions. How emotion is experienced and interpreted depends on how it is perceived. Likewise, how emotion is perceived is dependent on past experiences and interpretations. Emotion can be accurately perceived in humans. Emotions can be perceived visually, audibly, through smell and also through bodily sensations and this process is believed to be different from the perception of non-emotional material.
A functional account of emotions posits that emotions facilitate adaptive responses to environmental challenges. In other words, emotions are systems that respond to environmental input, such as a social or physical challenge, and produce adaptive output, such as a particular behavior. Under such accounts, emotions can manifest in maladaptive feelings and behaviors, but they are largely beneficial insofar as they inform and prepare individuals to respond to environmental challenges, and play a crucial role in structuring social interactions and relationships.
Fritz Strack is a German social psychologist and professor emeritus at the University of Würzburg. Strack is a member of Germany's National Academy of Sciences Leopoldina and was awarded the Ig Nobel Prize for psychology in 2019.
↑ Coles, N.A.; Larsen, J.T.; Lench, H.C. (2019). "A Meta-Analysis of the Facial Feedback Literature: Effects of Facial Feedback on Emotional Experience Are Small and Variable". Psychological Bulletin. 145 (6): 610–651. doi:10.1037/bul0000194. PMID30973236. S2CID108294841.
↑ Keillor, JM; Barrett, AM; Crucian, GP; Kortenkamp, S; Heilman, KM (January 2002). "Emotional experience and perception in the absence of facial feedback". Journal of the International Neuropsychological Society. 8 (1): 130–5. doi:10.1017/s1355617702811134. PMID11843071.
↑ Laird, James D. (1974). "Self-attribution of emotion: The effects of expressive behavior on the quality of emotional experience". Journal of Personality and Social Psychology. 29 (4): 475–486. doi:10.1037/h0036125. PMID4818323.
↑ Tourangeau, Roger; Ellsworth, Phoebe C. (1979). "The role of facial response in the experience of emotion". Journal of Personality and Social Psychology. 37 (9): 1519–1531. doi:10.1037/0022-3514.37.9.1519. PMID501520.
↑ McCanne, Thomas R.; Anderson, Judith A. (April 1987). "Emotional Responding Following Experimental Manipulation of Facial Electromyographic Activity". Journal of Personality and Social Psychology. 52 (4): 759–768. doi:10.1037/0022-3514.52.4.759. PMID3572737.
↑ Strack, Fritz; Martin, Leonard L.; Stepper, Sabine (1988). "Inhibiting and facilitating conditions of the human smile: A nonobtrusive test of the facial feedback hypothesis". Journal of Personality and Social Psychology. 54 (5): 768–777. doi:10.1037/0022-3514.54.5.768. PMID3379579. S2CID15291233.
↑ Soussignan, Robert (2002). "Duchenne smile, emotional experience, and autonomic reactivity: A test of the facial feedback hypothesis". Emotion. 2 (1): 52–74. doi:10.1037/1528-3542.2.1.52. PMID12899366.
↑ Wagenmakers, E.-J.; Beek, T.; Dijkhoff, L.; Gronau, Q. F.; Acosta, A.; Adams, R. B.; Albohn, D. N.; Allard, E. S.; Benning, S. D.; Blouin-Hudon, E.-M.; Bulnes, L. C.; Caldwell, T. L.; Calin-Jageman, R. J.; Capaldi, C. A.; Carfagno, N. S.; Chasten, K. T.; Cleeremans, A.; Connell, L.; DeCicco, J. M.; Dijkstra, K.; Fischer, A. H.; Foroni, F.; Hess, U.; Holmes, K. J.; Jones, J. L. H.; Klein, O.; Koch, C.; Korb, S.; Lewinski, P.; Liao, J. D.; Lund, S.; Lupianez, J.; Lynott, D.; Nance, C. N.; Oosterwijk, S.; Ozdoğru, A. A.; Pacheco-Unguetti, A. P.; Pearson, B.; Powis, C.; Riding, S.; Roberts, T.-A.; Rumiati, R. I.; Senden, M.; Shea-Shumsky, N. B.; Sobocko, K.; Soto, J. A.; Steiner, T. G.; Talarico, J. M.; van Allen, Z. M.; Vandekerckhove, M.; Wainwright, B.; Wayand, J. F.; Zeelenberg, R.; Zetzer, E. E.; Zwaan, R. A. (27 October 2016). "Registered Replication Report". Perspectives on Psychological Science. 11 (6): 917–928. doi:10.1177/1745691616674458. PMID27784749.
↑ Laird, James D. (1974). "Self-attribution of emotion: The effects of expressive behavior on the quality of emotional experience". Journal of Personality and Social Psychology. 29 (4): 475–486. doi:10.1037/h0036125. PMID4818323.
1 2 Strack, Fritz; Martin, Leonard L.; Stepper, Sabine (May 1988). "Inhibiting and Facilitating Conditions of the Human Smile: A Nonobtrusive Test of the Facial Feedback Hypothesis". Journal of Personality and Social Psychology. 54 (5): 768–777. doi:10.1037/0022-3514.54.5.768. PMID3379579. S2CID15291233.
↑ Böttger, D. (2010) To say "Krishna" is to smile - emotion psychology and the neurology of mantra singing. In "The Varieties of Ritual Experience" (ed. Jan Weinhold & Geoffrey Samuel) in the series "Ritual Dynamics and the Science of Ritual", Volume II: "Body, performance, agency and experience". Wiesbaden, Germany: Harrassowitz.
↑ (Noah T, Schul Y, Mayo R. (2018). When both the original study and its failed replication are correct: Feeling observed eliminates the facial-feedback effect. J Pers Soc Psychol. 2018 May;114(5):657-664. doi: 10.1037/pspa0000121.)
↑ McIntosh, Daniel N. (1996). "Facial feedback hypotheses: Evidence, implications, and directions". Motivation and Emotion. 20 (2): 121–147. doi:10.1007/BF02253868. S2CID3181718.
↑ Coles, N.A.; Larsen, J.T.; Lench, H.C. (2019). "A Meta-Analysis of the Facial Feedback Literature: Effects of Facial Feedback on Emotional Experience Are Small and Variable". Psychological Bulletin. 145 (6): 610–651. doi:10.1037/bul0000194. PMID30973236. S2CID108294841.
↑ Lewis, Michael B. (2012). "Exploring the positive and negative implications of facial feedback". Emotion. 12 (4): 852–859. doi:10.1037/a0029275. PMID22866886.
Lanzetta, John T.; Cartwright-Smith, Jeffrey; Kleck, Robert E. (1976). "Effects of Nonverbal Dissimulation on Emotional Experience and Autonomic Arousal". Journal of Personality and Social Psychology. 33 (3): 354–370. doi:10.1037/0022-3514.33.3.354. PMID1271216.
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