The title of this post doesn’t refer to the emotional or moral burdens of lying. Instead, I’m referring to the idea that lying is more taxing on your brain than telling the truth. Social psychologist Aldert Vrij of the University of Portsmouth in England believes the human mind can only think about so many things at once–your cognitive “load.” Vrij believes that by increasing the mental demands put on a person, you can exceed their cognitive load, and normal information processing will suffer. This compromised ability should reveal behavioral clues that would be very useful for law enforcement officers interrogating suspects.
Lying is more taxing than telling the truth because instead of simply telling someone the truth, the liar must remember two sets of facts simultaneously, keep them separate in his mind, think about how he appears while lying, and think about whether his listener knows that he is lying. If a law enforcement officer asks a potential liar to tell his stories in nontraditional ways, or to do certain things while answering questions, the liar’s cognitive load might be overwhelmed, and the liar might slip up. Once the slips begin, the liar’s story is likely to unravel. And unlike lie detector results, statements made during interrogation are admissible in court–the lies and the truth.
Vrij suggests several interrogation tactics, which they also described in a recent issue of Current Directions in Psychological Science. One tactic is to have suspects tell their story in reverse chronological order. This method of storytelling is more difficult than typical methods, increasing an already burdened cognitive load. This method proved very successful in Vrij’s lab. When observers watched videotapes of interviews, they correctly spotted only 42% of the lies people told when telling their stories normally (a below average rate, indicating the lies were hard to spot), but they spotted 60% of the lies when stories were told in reverse.
Another tactic was to require interview subjects to maintain constant eye contact with the interviewer. Liars will often look away in order to better concentrate on storytelling. The forced eye contact is an added distraction, making lying even more difficult. Again, in the lab, this tactic proved very successful.
A final tactic was to have interview subjects draw a picture of the events they have described during the interview. Although liars and truth-tellers often give the same number of verbal details, liars will often give far less detail in their drawing. Vrij believes this is because most liars do not prepare to describe things spatially, so their cognitive load is easily overwhelmed when they must quickly invent spatial details. The contrast between detailed stories and spartan drawings was found to be indicative of a lie.
The interrogation is a staple of police procedurals. Although showing a suspect a damning photo or threatening physical violence might be more dramatic, they are also rather cliched at this point. Increasingly, so too are stories featuring a “human lie detector.” What if your interviewer used some of these tactics instead? What if you disguised an infodump about these tactics in a threat or boast from an interviewer to a suspect? Let your suspect’s arrogance lead him into the trap that has just been laid out before him. Or what if you disguised the same infodump in a discussion between the suspect and another criminal? Maybe your suspect is prepared for these tactics?
What do you think? How can psychology help improve your interrogation scenes?