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How We Know You're Lying

Catching liars isn't easy, but there are a few reliable signs to look for

Few topics in psychology get as much attention as the telltale signs of deception. The emphasis on this topic has intensified tenfold over the last decade in response to terrorism, and a great deal of research has been initiated by Homeland Security and police departments as a means to inform and train their personnel.

One of the leading researchers in this field is UCLA professor of psychology R. Edward Geiselman. His studies have served as a the basis for training thousands of detectives, intelligence officers, police officers, and military personnel.

The sidebar benefit of all this research for us (in addition to the benefits of greater security) is that we can learn to nail liars in the act. A recent paper by Dr. Geiselman and three of his students in the American Journal of Forensic Psychiatry summarizes findings from 60 studies on detecting deception.

The most reliable indicators of lying, according to Geiselman, include:

  • When questioned, deceptive people say as little as possible
  • Though they say little, they tend to spontaneously give a justification for what they are saying, usually without being prompted
  • They tend to repeat questions before answering them
  • They carefully monitor the observer's reaction to what they are saying to judge whether their story is convincing or not
  • They start speaking slowly as they are creating their story and gradually get faster
  • They tend to speak in sentence fragments
  • They will often gesture to themselves and engage in "grooming behaviors" like playing with their hair (gestures toward oneself correlate strongly with deception; outward gestures correlate with truthfulness)
  • When pressed, liars will generally not provide more details, while truthful people will deny they are lying and provide more and more details of events to buttress their explanation
  • Truthful people tend to look away when answering a difficult question because they are concentrating, while liars will look away only briefly if at all

Geiselman also notes that when deceptive people attempt to cover up these typical reactions to lying, they become more obvious liars. The reason is that a liar's "cognitive load" is already high from manufacturing a story and trying to delivery it convincingly. Geiselman instructs his trainees on ways to increase this cognitive load to push the liar over the edge. Ways of doing this include:

  • Starting with general questions and then asking open-ended questions that require as much detail as possible.
  • Not interrupting the person when he/she attempts to answer -- simply let them attempt to fill out the story on their own
  • Asking that the person tell the story backwards ("Ok, let's review your story again, but this time let's rewind the tape and hear it the other way around")

How hard is it to catch liars? Very, according to Geiselman and Dr. Paul Ekman, another researcher who has devoted his career to identifying the signs of deception. In previous studies, Ekman found that without training, the average person's abilty to identify a liar is roughly the same as chance.

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