If we had to choose an absolute aspect that separates us humans from the rest of species, we would have to go with our uncanny ability to lie. Due to our propensity and expertise for creating artifice and deception, behavioral scientists have compiled volumes on research on how our physiology sometimes gets in the way of our attempts to conceal the truth.
Microexpressions are observations of brief, involuntary gestures that can be perceived on the human countenance as reactions to certain situations. Research into microexpressions has determined that they often occur when we are actively engaged in hiding our feelings and emotions; for example, when we try to hide our anger, our lower jaw sticks out a bit and some tension may develop around our lower eyelids.
It is important to note that microexpressions are not involuntary. Some people may deliberately resort to microexpressions for a number of reasons, sometimes they do it on account of feeling comfortable while other times they may actually be conscious of being monitored or studied. These controlled instances of microexpressions make detection and analysis very difficult, and thus it can be said that lie detection on these subtle facial expressions alone is a pseudoscience at best.
Detecting microexpressions requires paying very close attention to someone's visage. For this reason, detection is better accomplished with the aid of digital photography or film. Microexpressions can be detected during a one-on-one interaction, but as soon as the subject believes that he or she is being monitored, the process of detection may become compromised.
Common microexpressions can be grouped into seven categories:
Anger: Eye glare.
Contempt: The classic smirk and head tilt.
Disgust: Wrinkled nose and slightly raised upper lip.
Fear: Tense eyelids and lips stretched horizontally.
Happiness: Upturned corners of the lips and eyes.
Sadness: Unfocused eyes.
Surprise: Eyebrows raised for a split second.
It is important to note that microexpressions are very brief when they are involuntary. To this effect, someone whose gaze is pointed downward while lacking focus for several minutes can be determined to be really sad or faking sadness. This ambiguity can only be solved by investigating the situation as a whole and analyzing available information.
In the case of someone who appears to be happy, but who flashes the above-described microexpression of sadness for a brief second, deceit may be at play; however, a skilled prevaricator such as a spy may be able to manipulate his or her microexpressions for the purpose of further obfuscation.