Liars are nervous and therefore show nervous behaviors that observers can detect. This is the widespread view amongst the general public and professionals such as police and security personnel. Yet this is more a myth than a fact. Research has indeed shown that liars are typically more nervous than truth tellers. Research has also shown that observers (general public and professionals alike) pay attention to nonverbal signs of nervousness when they try to detect deceit. They pay particular attention to gaze aversion (looking away from the conversation partner) and fidgeting (scratching the hand, wrist, or head).
In fact, liars often do not show more nervous behaviors than truth tellers. There is typically no difference in gaze aversion between liars and truth tellers and liars typically make fewer rather than more movements than truth tellers.
Here’s why the myths are not true. First, the stereotypical view is that liars look away and fidget. Liars therefore actively try to suppress such behaviors to avoid making a suspicious impression. Second, lying often requires more mental effort than truth telling. Research has shown that hard thinking automatically decreases making movements because all the energy goes to the brain. This effect of thinking on making movements is easy to demonstrate. Ask someone to move around and clap their hands while saying the alphabet out loud: A, B, C, etc. Then ask the person to continue moving and hand clapping but now say the alphabet in reverse order: Z, Y, X, etc. You will see that the person will make fewer movements while saying the alphabet in reverse order.
Nonverbal cues to deception are, in fact, typically faint and unreliable. Most nonverbal cues are not related to deception at all and the most diagnostic nonverbal cue is the equivalent of the difference in height between a 15 and 16 year old girl. Such differences are too small to rely upon. Verbal cues to deceit—that is cues conveyed in the words people use—are typically more revealing, with the most revealing cue being the equivalent of the difference in height between a 14 and 18 year old girl—something easily noticed with the naked eye. It is therefore not surprising that if observers just have access to nonverbal cues when attempting to detect deceit, their ability to distinguish between lies and truths does not exceed chance. A large overview of such research showed an accuracy rate of 52%, which does not exceed flipping a coin (50%). However, when observers could only hear the person speaking, their accuracy rate was well above chance at 63%.
The main message for professionals therefore is that they should stay away from observing nonverbal behavior when they attempt to detect deceit in interviews and should listen to speech instead. Observing people’s behavior to detect deceit is culturally determined and reflects training. American professionals are often taught to pay attention to nonverbal behaviors and therefore tend to pay more attention to them than West European professionals, who are more frequently told that nonverbal cues to deception are weak and unreliable.
There is another good reason for professionals not to pay attention to nonverbal behaviors in interviews. The main purpose of an interview is to gather information from the interviewee. To obtain quality information an interviewer needs to listen carefully to what the person says so that they can come up with good follow-up questions. Listening to what someone says and thinking about the next question is already a task that requires much mental effort. To pay attention, on top of this, to the person’s nonverbal behavior becomes too much for the interviewer because it is impossible to listen to speech, observe behavior, and think about the next question all at the same time. Something has to go when interviewers observe nonverbal behaviors which will impair the information gathering part of the interview.
The limitation of listening to speech is that speech content is not always available. For example, take professionals tasked with identifying wrongdoers in public spaces, such as airports. Airports are typically too busy to interview all passengers, and professionals have no option other than observing behaviors when attempting to identify wrongdoers. Behavior Detection Officers (BDO-ers) across the world have been trained on what suspicious behaviors supposedly look like. Those training programs are limited, even those that are based on scientific research. The problem is that scientific research about how wrongdoers behave in such situations is largely absent. Virtually all research on nonverbal cues to deception has focused on how people behave during interviews when they speak. This is an entirely different setting compared to how people behave outside an interview setting when they often do not speak or may not even sit down.
In sum, research into nonverbal cues to deception has typically focused on how people behave in interview settings. The nonverbal cues they produce are typically weak and unreliable and less truly revealing than speech-related cues. Professionals are thus advised to stop observing behaviors in interviews and listen to speech instead.
For Further Reading
DePaulo, B. M., Lindsay, J. L., Malone, B. E., Muhlenbruck, L., Charlton, K., & Cooper, H. (2003). Cues to deception. Psychological Bulletin, 129, (1), 74-118. Doi: 10.1037/0033-2909.129.1.74
Vrij, A., Hartwig, M., & Granhag, P. A. (2019). Reading lies: Nonverbal communication and deception. Annual Review of Psychology, 70, 295-317. Doi: 10.1146/annurev-psych-010418-103135
Vrij, A., & Fisher, R. P. (2020). Unraveling the misconception about deception and nervous behaviour. Frontiers in Psychology, section Personality and Social Psychology, 11, 1377. Doi: 10.3389/fpsyg.2020.01377
Aldert Vrij is a professor of applied social psychology in the department of psychology at the University of Portsmouth in Portsmouth, England. His main area of expertise is nonverbal and verbal cues of deception.