Cognitive Connie
Understanding facial expressions of emotion
The human face is capable of producing more than 10,000 distinguishable configurations of muscle movements — yet only a small subset of these appear to carry emotional meaning across cultures. The scientific study of facial expression began with Darwin's 1872 book *The Expression of the Emotions in Man and Animals*, which argued that emotional expressions evolved because they communicated internal states and prepared the organism for action.
Defining features
Key figures
Guillaume-Benjamin Duchenne
1806–1875French neurologist who used electrical stimulation to map the facial muscles and identified that the orbicularis oculi — the muscle causing crow's feet and raised cheeks in genuine smiling — cannot be voluntarily contracted. The "Duchenne smile" bears his name.
Charles Darwin
1809–1882Naturalist whose 1872 book *The Expression of the Emotions in Man and Animals* proposed that emotional expressions have evolutionary continuity across species and communicate internal states. Darwin's functional and comparative approach anticipated the basic emotions tradition by nearly a century.
Wallace Friesen
1933–presentPsychologist and Ekman's long-term collaborator who co-developed the Facial Action Coding System. Friesen's cross-cultural work in Japan — showing identical physiological responses but different display behaviour in the presence of an authority figure — provided key evidence for the display rules framework.
Paul Ekman
1934–presentCo-developed FACS with Wallace Friesen and conducted the foundational cross-cultural studies of facial expression universality, including the Fore research in Papua New Guinea. His work defined the scientific agenda for facial expression research for five decades and led to wide applications in security, clinical psychology, and AI.
Lisa Feldman Barrett
1963–presentNeuroscientist who has led the most systematic empirical critique of the universality claim. Her 2019 meta-analysis concluded that facial expressions are not reliably decoded across cultures at above-chance levels for most emotions, challenging decades of assumed consensus. She argues that context and cultural knowledge are essential for expression interpretation.
Key concepts
Facial Action Coding System (FACS)
Developed by Ekman and Friesen (1978), FACS is an anatomically based system for coding all visible facial movements. Each movement is described as one or more of 44 Action Units (AUs) corresponding to specific muscles. FACS-coded data allows objective comparison across studies and is used in clinical, legal, and AI research.
Action Units (AUs)
The basic units in FACS — each AU corresponds to the contraction of one or more facial muscles. For example, AU6 (orbicularis oculi) raises the cheeks; AU12 (zygomaticus major) pulls the lip corners up. Combinations of AUs define emotional expressions: a genuine smile requires AU6 + AU12.
Duchenne smile
A genuine smile involving both the zygomaticus major (AU12, lip corners up) and the orbicularis oculi pars orbitalis (AU6, crow's feet and raised cheeks). Named after the French neurologist Guillaume-Benjamin Duchenne, who first identified that the orbicularis oculi is involuntary and thus distinguishes genuine from posed smiles.
Micro-expressions
Extremely brief (40–200ms), involuntary facial expressions that may leak genuine emotional states when a person is attempting to conceal their feelings. Ekman proposed that trained observers can detect them, though evidence for reliable detection — even with training — is mixed.
Display rules
Culturally and socially learned norms that prescribe how, when, and to whom emotions should be expressed. Strategies include amplification (exaggerating an expression), suppression (reducing or hiding it), masking (replacing one expression with another), and deamplification. Display rules explain why Japanese participants showed more neutral expressions in the presence of an authority figure in Ekman's studies, despite identical physiological responses.
Social referencing
The process by which infants look to a caregiver's facial expression to determine how to respond to an ambiguous situation. By 12 months, infants reliably use a caregiver's fearful or happy expression to decide whether to approach or avoid a novel object — a finding that demonstrates the communicative function of facial expression early in development.
Facial feedback hypothesis
The proposal that the physical act of making a facial expression can influence the subjective emotional experience associated with it. Fritz Strack's 1988 pencil-in-mouth study (inhibiting vs facilitating smiling) was highly influential but failed to replicate in a large pre-registered study, highlighting the difficulty of testing this hypothesis.
Emotional contagion
The automatic, largely unconscious tendency to mimic and synchronise facial expressions, vocalisations, postures, and movements with those of another person — resulting in convergence of emotional states. Elaine Hatfield and colleagues documented this as a primitive form of empathy operating below the level of conscious simulation.
Test your knowledge
Frequently asked questions
What is the Facial Action Coding System?+
FACS is an anatomically based coding system for facial movements developed by Ekman and Friesen (1978). It describes all visible facial behaviour in terms of 44 Action Units, each corresponding to one or more specific muscles. FACS allows researchers to objectively measure and compare facial expressions without making assumptions about their emotional meaning. It is widely used in emotion research, clinical psychology, and affective computing.
What are display rules and why are they important?+
Display rules are culturally learned norms governing when and how emotions should be expressed. They can require amplifying, suppressing, masking, or deamplifying emotional expressions depending on social context. Display rules explain why people from different cultures show different levels of emotional expressiveness without requiring that they actually feel different emotions — the same underlying feeling can be expressed very differently depending on who is watching.
Is the universality of facial expressions established?+
The claim was strongly supported by Ekman's original cross-cultural studies, especially the Fore research. However, replication studies using less constrained methods — such as free labelling rather than forced choice — show weaker cross-cultural agreement, and Barrett's 2019 meta-analysis found that agreement dropped substantially in methodologically rigorous studies. Current consensus is that there is some cross-cultural consistency in expression recognition, but less than Ekman claimed, and context plays a larger role than originally assumed.
What is a micro-expression and are they reliable?+
Micro-expressions are very brief (40–200ms) facial expressions proposed to reflect genuine emotions that a person is trying to conceal. Ekman proposed that trained observers can detect and interpret them. However, meta-analyses suggest that training programmes increase micro-expression detection only modestly, and the link between micro-expressions and deception is weaker than popular accounts suggest. Their use in lie detection contexts has been criticised by researchers as insufficiently supported.
Sources
Last reviewed July 2025- 1.
Ekman, P., & Friesen, W. V. (1978). Facial Action Coding System: A Technique for the Measurement of Facial Movement. Consulting Psychologists Press.
+About this source
Original FACS manual providing the anatomically-based coding system for all visible facial movements using 44 Action Units.
- 2.
Ekman, P., Sorenson, E. R., & Friesen, W. V. (1969). Pan-cultural elements in facial displays of emotion. Science, 164(3875), 86–88. https://doi.org/10.1126/science.164.3875.86
+About this source
Cross-cultural study including isolated populations providing the primary evidence for universality of facial expressions.
- 3.
Barrett, L. F., Adolphs, R., Marsella, S., Martinez, A. M., & Pollak, S. D. (2019). Emotional expressions reconsidered: Challenges to inferring emotion from human facial movements. Psychological Science in the Public Interest, 20(1), 1–68. https://doi.org/10.1177/1529100619832930
+About this source
Comprehensive meta-analysis challenging the universality claim and showing facial expressions do not reliably predict emotional states.
- 4.
Darwin, C. (1872). The Expression of the Emotions in Man and Animals. John Murray.
+About this source
Foundational evolutionary account of emotional expression proposing communicative function and cross-species continuity.