Microexpressions n.
The presence of a microexpression does not confirm deception; it signals emotional concealment, which may occur in honest and deceptive contexts alike.
The definition
Microexpressions are involuntary facial expressions lasting between 1/25 and 1/5 of a second that briefly reveal concealed or suppressed emotional states. First codified within Paul Ekman's Facial Action Coding System, they represent emotional leakage: a spontaneous neuromuscular discharge covering seven universal emotion categories that escapes deliberate suppression before conscious masking can take effect.
2%
of coded facial expressions were true microexpressions in controlled lab conditions
PORTER & TEN BRINKE · 2008 2
The mechanism
A microexpression occupies a window of 1/25 to 1/5 of a second, placing it well below the threshold of conscious awareness for most untrained observers 1. Despite this brevity, the same facial action units active in full-duration macro-expressions engage; the neuromuscular pathway is identical. Ekman's cross-cultural research identified seven emotion categories generating consistent action unit patterns regardless of cultural origin: happiness, sadness, fear, anger, disgust, contempt, and surprise 1. Each category maps to a discrete configuration of the facial musculature.
The mechanism that produces a microexpression is affect suppression failure. When a person attempts to mask or neutralise an emotional response, the underlying state briefly activates the same neuromuscular pathways as a complete expression before deliberate control intervenes 2. Porter and ten Brinke demonstrated this empirically: participants asked to conceal negative emotions produced inconsistent facial expressions in every coded sequence, confirming that emotional leakage is effectively universal under suppression conditions 2. The pattern resembles a hydraulic valve: the emotional signal exits before the deliberate seal can engage.
In practice
The microexpression's significance lies not in what it confirms about deception, but in what it reveals about an emotion the person chose not to show.
Worked example
A senior executive presents a contract proposal with a composed expression and measured tone. When a specific clause is read aloud, her face displays a half-second configuration consistent with contempt before her expression resets to neutral. The verbal discussion continues as if nothing occurred. An observer trained to register action units would note the discrepancy and probe the clause in follow-up.
The microexpression did not reveal deception; it revealed an unexpressed evaluation worth investigating.
Why it matters
The stakes of microexpression science extend in two directions that practitioners frequently conflate. As a mechanism, the theory of affect suppression producing brief neuromuscular leakage is empirically well-supported: Porter and ten Brinke found emotional leakage occurring in every participant who attempted to conceal a negative emotion 2. As a deception-detection tool, the case is substantially weaker. True microexpressions constituted only 2% of all coded facial expressions in controlled conditions and appeared equally in honest and deceptive displays 2.
Burgoon's systematic analysis identified detection accuracy near chance for observers relying on microexpressions alone, and independent testing by Jordan et al. confirmed that the Micro-Expressions Training Tool conferred no advantage over baseline or sham training on lie-detection accuracy 3 4. The practical reorientation Burgoon recommends is to attend to temporal patterning and behavioural rigidity across a full interaction rather than any single brief expression 3. Microexpressions signal emotional concealment; they do not confirm deception, and the two conditions are not equivalent.
Questions of record
How long does a microexpression last?
A microexpression lasts between 1/25 and 1/5 of a second. This duration places it below the threshold of conscious detection for most untrained observers. The underlying facial action units are identical to those in full-duration expressions; only the time window differs.
Are microexpressions reliable indicators of deception?
No. Controlled research found true microexpressions in only 2% of coded expressions, distributed equally across honest and deceptive displays. Detection accuracy for observers relying on microexpressions alone falls near chance. They signal emotional concealment, not deception, and the two conditions are not equivalent.
Can microexpression training improve lie detection?
Independent testing of the Micro-Expressions Training Tool found no advantage over baseline or sham training on lie-detection accuracy; overall performance was slightly below chance. Commercial programmes deploy widely in law enforcement and clinical settings, but the independent evidence for improved accuracy is limited.
What are the seven universal emotions shown in microexpressions?
Ekman's cross-cultural research identified happiness, sadness, fear, anger, disgust, contempt, and surprise as the seven universal emotion categories producing consistent facial action unit patterns across cultures. Each maps to a specific configuration of facial muscles regardless of the observer's cultural background.