Abstract: When an emotion is concealed or repressed, the true emotion may be manifest as a micro-expression, a fleeting facial expression discordant with the expressed emotion, usually suppressed within 1/25 to 1/5 of a second, and closely related to the deception. This article is a review of all the studies reported about micro-expression. Earlier researchers focused on the measurement of abilities to recognize micro-expression. Because of the development of measurement tools, a large number of micro-expression recognition studies emerged within the clinical domain. However, only one published empirical study has explored the generation of micro-expression, and many questions are left unanswered. Further research should focus on the cross-culture validity of Micro-Expression Training Tool (METT), the generation of micro-expression, and the development of automatic micro-expression recognition tools. Micro-expression studies can provide important insights into the development of an automatic deception detection system.

Key words: micro-expression, deception, micro-expression recognition, micro-expression generation