By Doctors David Matsumoto, Hyi Sung Hwang, Lisa Skinner & Mark Frank
FBI Law Enforcement Bulletin
While interviewing the suspect who claims ignorance about an incident, the witness who saw it happen, or the informant who identified the perpetrator, the detective asks a question that will eviscerate the perpetrator’s story. As the suspect prepares to answer, he looks up and to the left, purses his lips, tenses his eyelids, and brings his eyebrows down.
The investigator knows that a suspect displaying shifty eyes and gaze aversion and looking up and to the left when answering uncomfortable questions is exhibiting signs of lying. The suspect is not totally disinterested, but he is reluctant to participate in the interview. Because the suspect’s behavior suggests dishonesty, the detective prepares to drill still deeper in the questioning.
Unfortunately, this investigator likely would be wrong. Twenty-three out of 24 peer-reviewed studies published in scientific journals reporting experiments on eye behavior as an indicator of lying have rejected this hypothesis.1 No scientific evidence exists to suggest that eye behavior or gaze aversion can gauge truthfulness reliably.
Some people say that gaze aversion is the sure sign of lying, others that fidgety feet or hands are the key indicators. Still others believe that analysis of voice stress or body posture provides benchmarks. Research has tested all of these indicators and found them only weakly associated with deception.2
Relying on false clues, or signs, about lying can have dire consequences.3 It can lead to inaccurate reads that witnesses, suspects, or informants are lying when they are not or that they are telling the truth when there is more to the story. Reliance on false clues leads to misplaced confidence about the strengths and weaknesses of cases and can lead an investigator down dead-end paths. Moreover, a false read can have deadly consequences.
Years of research have led the authors to focus solely on the most verifiable behavioral cues to lying.4Many studies have involved a randomly selected sample of people assigned by chance to lie or tell the truth. Unfortunately, such studies feature participants with no personal, financial, or emotional investment in the lie or any fear of exposure to sanction if they are caught. No stakes are involved—no punishment for getting caught and no reward for fooling the investigator.
The authors’ studies involve people motivated to act against a person or group with a different ideology, placed in a situation where they choose whether to commit a crime (e.g., steal a check made out to the group they despise), and then interviewed by a retired law enforcement officer, offering them the opportunity to tell the truth or lie. The stakes involved include facing detention, enduring blasts of white noise, or, for instance, having the stolen check donated to the group they hate. These consequences would occur if the person were not believed regardless of the truth because, in real life, consequences stem from judgments, not reality. Thus, truthful individuals often are nervous in police interrogations. The authors strive to make their research practical and analogous to real-world law enforcement situations and have found that, clearly, the behavioral cues to lying differ when people are not vested in having their story believed and have no fear of detection.
The authors monitor their participants with sensors that record and analyze their facial behaviors, gestures, body movements, voice and speech characteristics, physiological indicators (e.g., heart rate, blood pressure, skin conductance, respiration), heat emanation from their faces and heads, pupil dilation, and gaze direction. In addition, the authors record their participants’ spoken words and then examine their verbal statements and style. The results have demonstrated that when motivated people lie and face consequences upon detection, clues to deception emerge and appear as leakage across multiple channels. Four of these are nonverbal (facial expressions, gestures and body language, voice, and verbal style). A fifth channel of leakage is in the actual words spoken—verbal statements.
It is not the mere presence or absence of behaviors, such as gaze aversion or fidgeting, that indicates lying. Rather, it is how these nonverbal cues change over time from a person’s baseline and how they combine with the individual’s words. And, when just the behavioral cues from these sources are considered, they accurately differentiate between lying and truth telling.5