The Science of Facial Expression — From Ekman's Basic Emotions to Microexpressions

The face conveys the interior ahead of one's own intention. Tension, relief, contempt, interest — a slight movement of facial muscle frequently orients the listener's judgement before a word is spoken. This volume reconstructs the science of "the face" by tracing 150 years of accumulated work. Charles Darwin's universality hypothesis (1872), Duchenne's discovery of the "true smile" (1862), Paul Ekman's basic six emotions and the FACS, microexpression research, Strack et al.'s facial-feedback hypothesis and the replication controversy, and the wisdom of the Noh mask — seven perspectives draw out the practice of composing the face. At the same time, the limits of facial-expression research (objections to Ekman's universality, the failed replication of Strack 1988, Coles 2022's multi-lab reassessment) are conveyed without exaggeration. The face can certainly be honed as technique — but it does not become a tool of deceit. This is the central proposition of the volume.

01The Face Carries a Message — A Language Without Words

In Vol. 4 we argued that voice conveys the internal state ahead of the words. The face is an even stronger information source. The listener is reading the face unconsciously — picking up the signals of tension, relief, contempt, interest almost automatically. This is part of the structure of cognition, and we cannot stop it.

The implication for the reviewer is clear. Facing a requester, delivering a correction, entering a hard negotiation — the face has already spoken. Before one is conscious, the listener has received the signal. For just this reason, the practice of knowing the structure of the face and composing it consciously becomes the practice for carrying the impression of confidence and sincerity.

In this volume, tracing the science of facial expression from Darwin in the nineteenth century to multi-lab replication in the twenty-first, we distinguish what is established, what is contested, and what can be brought down into daily practice — without exaggeration, but without dismissal either.

02Darwin's Precursor — The Universality Hypothesis of Facial Expression

The starting point of facial-expression research is Charles Darwin's (1809–1882) The Expression of the Emotions in Man and Animals (1872). A work that extended the evolutionary theory of On the Origin of Species (1859) to the bodily expression of emotion.

"The principal expressions exhibited by humankind are the same throughout the world. This is evidence of evolutionary continuity, and human emotional expression is not a culturally acquired construction but a biological inheritance." — paraphrase of Charles Darwin, The Expression of the Emotions in Man and Animals (1872)

Darwin sent questionnaires to missionaries and colonial officials around the world, having them observe the facial expressions of local populations. He collected evidence that the expressions of joy, sadness, fear, surprise — the principal emotions — were similar across cultures. By contemporary standards this is methodologically crude, but it was the first systematic attempt to put forward the hypothesis that facial expression may transcend culture.

The hypothesis then lay dormant for about a hundred years, and did not return to the centre of psychology until Paul Ekman restarted it empirically in the 1960s. In the intervening era, cultural relativism — "culture makes facial expression" — dominated psychology.

03Duchenne's "True Smile" — Electrophysiology of 1862

In 1862, almost contemporaneous with Darwin, the French neurologist Guillaume-Benjamin Duchenne (1806–1875) carried out, in Mécanisme de la physionomie humaine, the astonishing experiment of separating the facial muscles that make expression and observing them through electrical stimulation.

"When a weak current is applied to contract a specific facial muscle, the muscle that lifts the corner of the mouth (zygomaticus major) alone produces only an apparent smile. A true smile of joy requires the contraction of another muscle — the orbicularis oculi (around the eye). The orbicularis oculi cannot be entirely controlled by will." — paraphrase of Guillaume-Benjamin Duchenne, Mécanisme de la physionomie humaine (1862)

Duchenne's discovery was later named by Ekman and others the "Duchenne smile" (the true smile). A genuine smile of joy moves not only the mouth corner but the muscles around the eye as well. A consciously fashioned smile moves only the mouth corner; the eye does not change — this is the physiological boundary between the "fake smile" and the "true smile."

Two implications. First, the listener is unconsciously observing the movement around the eye. A fake smile is detected by most people. Second, the smile of one who feels genuine joy naturally reaches the eyes. The implication for the reviewer is clear — rather than putting on a smile, the practice of evoking a genuine positive feeling from within is what makes a true smile.

04Ekman's Basic Six — Universality That Transcends Culture

The one who restarted Darwin's hypothesis empirically is the American psychologist Paul Ekman (1934–). From the 1960s through the 1970s, he conducted experiments on facial-expression recognition in many parts of the world, including with isolated tribes of Papua New Guinea (the Fore people).

"People of every culture in the world, looking at the same photograph of a facial expression, read the same emotion. The expressions of the six basic emotions — joy, sadness, anger, fear, surprise, disgust — are universal across culture." — paraphrase of Ekman & Friesen, JPSP (1971)

Ekman called these the "basic six expressions." Later he proposed adding contempt as a seventh. His claim revived Darwin's universality hypothesis empirically and brought psychology back from cultural relativism to a horizon of universality.

* Caution is required, however. In the twenty-first century, Ekman's universality claim has come under strong critique from Lisa Feldman Barrett (1963–) of Northeastern University and others. Barrett's critique is that the correspondence between facial expression and emotion depends heavily on culture and context, and that the universality Ekman demonstrated was methodologically overstated. This volume acknowledges the dispute and takes the position that Ekman's basic framework is useful in practice as a convenient coordinate system.

05FACS and the Anatomy of Expression — Decomposing the Movement of the Face

In 1978, Ekman, together with Wallace Friesen, published the FACS (Facial Action Coding System). This is a system that decomposes the movement of the face into 44 Action Units (AUs) and describes every expression as a combination of AUs.

"Classifying expressions roughly as 'smile' or 'angry face' is convenient but too coarse for research. By decomposing into the movement of each facial muscle (AU), expression can be observed and recorded objectively. AU6 (orbicularis oculi) + AU12 (zygomaticus major) = Duchenne smile. AU12 alone = fake smile." — paraphrase of Ekman & Friesen, FACS Manual (1978; rev. 2002)

FACS has two significances. First, it transformed facial-expression research into a quantifiable science. Second, it provided the foundation for the later affective computing (AI-based facial-expression recognition). Many contemporary AI facial-expression systems infer emotion by detecting FACS AUs.

The reviewer does not need to memorise the whole of FACS. But the implication is clear — facial expression is a combination of decomposable elements, and each element can be consciously observed and adjusted. Raise the brow, lift the mouth corner, relax the muscle around the eye — each is an independent movement.

06Microexpression — The Truth of 1/25 of a Second

The other axis of Ekman's facial-expression research is the microexpression. This is an expression that appears on the face for an extremely brief time — 1/25 to 1/15 of a second, said to be the moment in which the emotion one is consciously trying to hide leaks. It became widely known through Ekman's book Telling Lies (1985).

"When a person tells a lie, they try to erase their genuine emotion from the face. But in many cases, in the 1/25 of a second before the effort begins, the expression of the real feeling leaks for an instant. This is the microexpression. With training, it can be detected." — paraphrase of Paul Ekman, Telling Lies (1985)

Microexpression research was applied to airport security, including the U.S. TSA's Behavior Detection Officer program. But here too there is scientific dispute. The independent replication results are mixed on whether microexpression detection is actually effective at lie detection. The U.S. Government Accountability Office (GAO) questioned the scientific basis of the TSA's behaviour-detection program in a 2013 report.

The treatment in this volume is conservative. Microexpression is an important observation of the phenomenon that "a person cannot entirely erase the true feeling from the face," and an attentive interlocutor can consciously read the expression — but to over-trust it as "lie-detection technology" is dangerous. This is the contemporary standard understanding. The implication for the reviewer is that one's own expression may also unintentionally leak the true feeling. Therefore the composition of the internal state (the "Outside → Inside" circuit of Vol. 3) is directly tied to the composition of the face.

07The Facial Feedback Hypothesis — Does Smiling Make You Happy?

The application of William James's body-first hypothesis (treated in Vol. 3) to facial expression is the facial feedback hypothesis. If one makes a smiling expression, a happy mood arises afterwards. The paper that made this hypothesis most famous is Strack-Martin-Stepper (1988).

"Subjects who read cartoons while holding a pen horizontally between the teeth (mouth corners up = the smile muscles move) found the cartoons funnier than subjects holding the pen vertically (mouth corners down = the frown muscles move). The expression itself influences feeling." — paraphrase of Strack, Martin & Stepper, JPSP (1988)

This experiment became extraordinarily famous and was repeatedly cited in textbooks and TED Talks. But here a scientifically important event occurred. In 2016, a Registered Replication Report by Wagenmakers and 17 laboratories reported that they could not reproduce the Strack et al. result. This became one of the symbolic cases of the "replication crisis."

The story has a further development. In 2022, the Many Smiles Collaboration led by Nicholas Coles (19 countries, 25 laboratories) re-examined the hypothesis by more refined methods and concluded that the facial feedback effect exists, but the effect size is smaller than Strack et al. demonstrated. The smile makes the mood — but modestly. This is the scientific consensus of the 2020s.

The practical implication for the reviewer. Before a difficult meeting, smile consciously. That is not "fabricating a false happiness" but a help in lifting the internal state slightly. Do not expect too much, but neither dismiss.

08The Wisdom of the Noh Mask — Concealing in Order to Express

From the East, the wisdom of facial expression. Japanese Noh is a paradoxical tradition that performs while wearing the mask (omote) — that is, expressing by erasing the face. This technique, completed since the time of Zeami (c. 1363 – c. 1443), holds wisdom that reaches contemporary research on facial expression.

"The Noh mask is not expressionless. By a slight change of angle — looking up clouds it, looking down brightens it — it expresses infinite feeling. By erasing the expression, the audience gains the margin to project its own feeling. This is the power of the mask." — paraphrase of Kanze Hisao, Kan'ami / Zeami (1980)

The wisdom of the Noh mask carries two implications. First, excessive expression impoverishes expression. What looks rich is in fact monotonous. Second, a slight angle, breath, and ma carry the greatest feeling. This resonates, from a different direction, with Ekman's discovery of microexpression — small movement of the face carries great meaning.

The implication for the reviewer. Both excessive smile and excessive solemnity create an unnatural impression. The wisdom of the Noh mask is the art of restraint — conveying much with slight movement of expression. "Neither too far up nor too far down" — this is not only metaphor; it is also, literally, the practice of the angle of the face.

09In the Pharmaceutical Workplace — What the Reviewer's Face Carries

Let us bring the abstract down to the field. Concrete scenes in the reviewer's daily work in which the face is tested.

10Five Practices for Composing the Face

To bring the same place to which the seven traditions pointed down into daily practice, five practices are set here.

Facial expression conveys the interior ahead of one's intention — 150 years of facial-expression science have pointed, in different words, to the same place. Darwin's universality hypothesis, Duchenne's true smile, Ekman's basic six and FACS, microexpression research, the Strack-Martin-Stepper facial feedback hypothesis and the Coles multi-lab reassessment, the technique of restraint of the Noh mask. Each claim has its limits and disputes, and this volume has conveyed them without exaggeration. The face can certainly be composed as a technique — but it does not become a tool of deceit.

A true smile arises naturally from an internal state. A microexpression cannot be entirely erased by will. Excessive expression-management runs against the wisdom of the Noh mask. For just this reason, the practice of composing the face cannot be separated from the practice of composing the internal state. The body-first circuit treated in Vol. 3, the embodiment of voice treated in Vol. 4 — and now the face — all are parts of the spiral structure in which inside and outside make each other.