Microfacial Expressions

Microfacial expressions, more commonly called microexpressions, are involuntary and fleeting facial expressions that reveal an individual's experience of an emotion. Microexpressions can last anywhere from 1/5 to 1/25 of a second. The seven basic facial expressions—happiness, sadness, anger, contempt, surprise, fear, and disgust—can all be expressed as microexpressions. Research indicates that the stronger the emotion the more difficult it is to conceal, with fear being the most difficult to conceal and happiness the easiest.

Microexpressions were first described in the 1960s by researchers examining nonverbal communication during psychotherapy sessions. The researchers slowed the videotapes of patient and therapist interactions to discover “micromomentary” expressions produced by patients that lasted less than one-fifth of a second. Paul Ekman and his colleagues later connected microexpressions to the concept of deception detection by theorizing that microexpressions were involuntarily leaked emotions associated with the deception, such as guilt, shame, or anger, that a person was trying to mask, or the feigning of an emotion, such as smiling when upset. Ekman noted that the face has many muscles that are not typically under voluntary control, making microexpressions difficult to feign, while nonverbal behaviors in the rest of the body can be masked through conscious effort.

The use of microexpressions as a method for detecting deception quickly became popular among professionals in the deception detection field. Police manuals and training programs frequently discussed microexpressions as an important tool for detecting deception, often with claims that microexpression analysis could lead to high-accuracy deception detection. Microexpression's usefulness for detecting deception was also popularized for the general public, with television shows such as Lie to Me showing the main character catching liars through his ability to identify microexpressions.

An airport agent checks a passenger's identification before allowing her to proceed through security, March 29, 2013. A large-scale, controversial program called Screening Passengers by Observational Techniques is based on detecting microexpressions.

Despite professional and popular conceptions of microexpressions, however, there have been few peer-reviewed scientific articles that have examined the relationship between microexpressions and deception. The first peer-reviewed study to examine the relationship between microexpressions and deception was not published until 2008, and found only partial support for Ekman's idea that microexpressions can reveal a masked emotion. Consistent with that idea, microexpressions occurred more often when participants were trying to mask an emotion, especially under higher stakes, than during genuine expressions. Microexpressions, however, were also observed during genuine emotional displays, indicating that they are not solely related to masked emotions. Additionally, microexpressions were rarely full-face emotional expressions; rather, what often were leaked were partial expressions occurring only in smaller, specific areas of the face. Overall, microexpressions were extremely rare, suggesting that they may not be very useful in detecting deception in general. Further, microexpressions may not be as “micro” as previously believed, with some of the inconsistent expressions lasting more than one second.