APA Dictionary of Psychology

a coding system for classifying facial expressions in terms of the movements of particular facial muscles, such as the orbicularis oculi (the muscle encircling each eye) and the zygomaticus major (the muscle pulling the corners of the lips upward). Elaborations of this system have been used in attempts to identify the emotional state of a person. True happiness, for example, is said to be indicated by contraction of the orbicularis oculi muscle, which is not under conscious control. Compare Maximally Discriminative Facial Movement Coding System. See also Duchenne smile; facial expression. [first published in 1978 by U.S. psychologists Paul Ekman (1934–  ) and Wallace V. Friesen (1933–  )]