One of my guilty pleasures is the long-running TV show NCIS, a drama focused on the Naval Criminal Investigative Service. The hero is a former marine, now Special Agent Jethro Gibbs, a disciplined detective with an uncanny ability to observe and question criminal suspects. Gibbs doesn’t say much or display a lot of emotion in the interrogation room—indeed, his cool demeanor is his trademark—yet he is a keen lie spotter.
Psychological scientists are fascinated by real-life versions of the fictional Gibbs. Detecting lies and liars is essential to effective policing and prosecution of criminals, but it is maddeningly difficult. Most of us can correctly spot barely more than half of all lies and truths through listening and observation—meaning we are wrong almost as often as we are right. And half a century of research has done little to polish this unimpressive track record.
But scientists are still working to improve on that, and among them is social psychologist Aldert Vrij of the University of Portsmouth in England. Vrij has been using a key insight from his field to improve interrogation methods: the human mind, despite its impressive abilities, has limited capacity for how much thinking it can handle at any one time. So piling on demands for additional, simultaneous thought—or cognitive “load”—compromises normal information processing. Because lying is more cognitively demanding than telling the truth, these compromised abilities should be revealed in detectable behavioral clues.
Why is lying more demanding? Imagine for a few minutes that you’re guilty of a murder, and Gibbs is cross-examining you. To start, you need to invent a story, and you also have to monitor that tale constantly so it is plausible and consistent with the known facts. That task takes a lot of mental effort that innocent truth tellers do not have to spend. You also need to actively remember the details of the story you’ve fabricated so that you don’t contradict yourself at any point. Remembering a fiction is much more demanding than remembering something that actually occurred. Because you’re worried about your credibility, you’re most likely trying to control your demeanor, and “looking honest” also saps mental energy. And you’re not just monitoring yourself; you’re also scanning Gibbs’s face for signs that he might be seeing through your lie. That’s not all. Like an actor, you have the mental demands of staying in character. And finally, you have to suppress the truth so that you don’t let some damning fact slip out—another drain on your mind’s limited supply of fuel. In short, the truth is automatic and effortless, and lying is the opposite of that. It is intentional, deliberate and exhausting.
Testing the Limits of Lying
So how could Gibbs and other detectives exploit the differing mental experiences of liars and truth tellers? Here are a few strategies that Vrij and his colleagues have been testing in the laboratory, which they describe in a recent issue of the journal Current Directions in Psychological Science.
One intriguing strategy is to demand that suspects tell their stories in reverse. Narrating backward increases cognitive load because it runs counter to the natural forward sequencing of events. Because liars already have depleted cognitive resources, they should find this unfamiliar mental exercise more taxing than truth tellers do—which should increase the likelihood that they will somehow betray themselves. And in fact, that is just what happens in the lab: Vrij ran an experiment in which half the liars and truth tellers were instructed to recall their stories in reverse order. When observers later looked at videotapes of the complete interviews, they correctly spotted only 42 percent of the lies people told when recounting their stories without fabrication—below average, which means they were hard to spot—but a remarkable 60 percent when the liars were compromised by the reverse storytelling.