A nose scratch, a mouth cover, hand wringing, leg tapping, looking away when answering—over the years, different claims have been made about these and other nonverbal behavior (NVB) as possible cues to deception. But what’s the truth?
Recent years have seen a shift away from leveraging behavioral indicators of deception in investigative interviewing. This push has been led by well-known researchers who invariably cite a landmark meta-analysis published two decades ago. That study reported a remarkable amount of work; the authors assembled hundreds of studies, extracted over 1,000 estimates of 158 behavioral cues, and statistically analyzed whether each of those cues individually differentiated truths from lies. The findings were indeed underwhelming:
“Liars are less forthcoming than truth tellers, and they tell less compelling tales. They also make a more negative impression and are more tense. Their stories include fewer ordinary imperfections and unusual contents. However, many behaviors showed no discernible links, or only weak links, to deceit.”
Given those findings, there is little wonder that many shied away from the notion of behavioral indicators of deception.
But now, behavioral indicators of deception are getting a new look. A re-examination of the methodologies used in the seminal meta-analysis mentioned above led to this more accurate conclusion: Few, if any, single NVB differentiated truth tellers from liars in low stakes lies or when suppressing emotions, feelings, or pain when no one else is around. Clearly, this statement does not apply to loss prevention investigators. On the contrary, when LP investigators talk to someone, they actually talk with them (interviewees are not alone asked to suppress their feelings) and there are stakes involved—someone may be arrested or lose their job.
Equally important, many studies published in the last two decades have demonstrated that NVB can differentiate truth tellers and liars fairly well. One reason why these different findings have emerged is that these studies have examined moderate- to high-stakes lies in actual investigative interviews, which is more congruent with the types of interviews LP professionals conduct. In the remainder of this article, I describe three main takeaways for practitioners considering the latest studies in this area.
Takeaway 1: Identify Clusters of Nonverbal Behavior Across Multiple Channels
NVB can differentiate truth tellers and liars fairly well when clusters of NVB are examined across multiple channels. Thus, unlike myths surrounding single behavior (eyes looking away when answering, covering the mouth when talking, etc.) investigators should focus on clusters of NVB produced in multiple channels of behavior, across the face, voice, hands, and whole body. Examining clusters makes more sense because NVB are part of a total communication package that occurs across multiple channels, with and without words. This view is based on the neural wiring in our bodies that connects our thoughts and feelings, the blending of cognitions and emotions at any one time and across time, the fact that people verbalize only portions of their mental contents, and that different mental states map onto different NVB channels.
Takeaway 2: Focus on Behavioral Indicators That Have Been Validated in Science and Vetted in the Field
Don’t believe everything about NVB that you may hear or read about. Certain NVB have been scientifically validated as deception indicators while others have not. On one hand, facial expressions of emotion and micro-expressions, some types of gestures, fidgeting (in some contexts), and some aspects of voice differentiate truth tellers from liars. Moreover, some behaviors are indicators of veracity while others are indicators of deception. On the other hand, looking away when answering questions (gaze aversion) has not been scientifically validated as a deception cue. In fact, liars are more likely to look interviewers in the eye when answering in order to compensate for that idea; thus, gaze aversion when lying is more a myth than reality—a myth that is believed by many around the world, and investigators may do well to not rely on that behavior as a deception indicator.
Takeaway 3: Nonverbal Behaviors Are Also Important Indicators of Other Mental States That Can Be Helpful for Investigators
NVB can signal many different mental states beyond veracity and deception, all of which can be useful to investigators as landmarks of meaningful topics and themes. These include specific, discrete emotions such as anger, disgust, or fear; general affective states such as open or closed, relaxed or tense; specific verbal words or phrases; cognitive processes, confusion, or concentration; and others. Identifying these behaviors can give investigators additional insights into people’s mindsets. When produced with words, NVB can complement, supplement, qualify, and contradict words; even without words, NVB can provide additional insights about people’s mental states without them talking. Identifying these types of mental states through behavioral signals can be important information to any investigator.
Experienced practitioners know their optimal strategies that fit based on their cumulative experiences. Among the customized strategies each investigator may have, the accurate and reliable observation and classification of NVB can be a crucial aid. Focusing on NVB clusters that have been validated in science and vetted in field work is key. Equally important is ignoring NVB that have not been validated. By knowing which behaviors have been validated and vetted and which have not, investigators can become more efficient by distinguishing meaningful signals from noise in the behavioral mess that occurs in the interview.
None of this minimizes the incredible importance of words and specific linguistic and grammatical features of speech. Contradictions, inconsistencies, obfuscation, and many linguistic features are also critically important to notice. By focusing on both verbal and NVB that have been validated in science and vetted in the field, investigators can truly have a force multiplier in their interviewing strategies and tactics. Combining enhanced verbal and NVB indicator assessment with evidence-based interviewing strategies and tactics and the tactical use of evidence such as witness statements, forensics, or video data can improve interview efficiency and effectiveness. When trained on validated verbal and nonverbal indicators, not only does deception detection ability increase but also interview efficiency and effectiveness.
Dr. David Matsumoto, Director of Humintell, is a world-renowned expert in the fields of emotion, nonverbal behavior, deception, and culture. He was a Professor of Psychology at San Francisco State University for over 30 years, and was the Founder and Director of SFSU’s Culture and Emotion Research Laboratory.