Self-reporting shows that, on average, people lie twice a day. When detecting lies, a standard image may rise of people with sweat on their foreheads or people who continuously look away during a conversation. Sophie van der Zee, legal psychologist and director of the Centre for the Law and Economics of Cybersecurity (CLECS), studies lie detection and nuances this standard image of lie detection. She distinguishes facts from fiction and points out other ways to detect liars. Although not every lie is harmful and worthy of detection, Van der Zee’s insights are valuable. After all, what if someone is suspected of a crime and does not appear to be telling the truth?
People turn out to be faulty lie detectors. According to Van der Zee, the chances of catching someone in a lie if you are actively trying are only 54%. Hence, detecting lies almost comes down to a matter of heads or tails. Van der Zee explains that this is partly because people focus on the wrong recognition points. For instance, liars are wrongfully assumed to constantly look away when they tell a lie. And even though liars can get a dry mouth due to a physiological stress reaction, this does, however, not mean that if someone takes a sip of water, they are necessarily a liar since nervousness can also have other causes.
Asking the right questions
Van der Zee offers a box full of tricks to detect lies, for instance, if people are suspected of a criminal offence. First, it is important to ask people the right questions, such as questions about verifiable details. A liar wants to give details without being caught, so the liar is more likely to give details that cannot be verified. A second way to trick a liar is to let this person tell a story backwards rather than in a chronological – and often rehearsed – order. This increases the cognitive load of a lie. Finally, you can ask suspects about the weaknesses in their own stories. A liar will probably point out fewer weaknesses in their lie because they do not want to give the other person any ideas.
“Both police and judges in the Netherlands are strongly convinced that the moment a story is consistent, it will probably be reliable. If a story is not so consistent – that is, if there are differences between statements – they are assumed not to be trustworthy”, Van der Zee explains. However, the research of Van der Zee and her colleagues shows that the stories of people who lie generally turn out to be more consistent except when it concerns evidence. “We know that when someone says A but shows evidence B, this is a good indicator of a lie”, Van der Zee states.
Additional detection techniques
Because the use of the polygraph, better known as a technological lie detector, is banned in the Netherlands and because such detection can be relatively easily bypassed by liars, Van der Zee is looking for new techniques. For example, she looked at motion capture suits. These suits map how much people move. Most people appear to move more when they lie. Van der Zee also pays attention to so-called mirroring, in which liars mirror their conversation partner in their movements. Moreover, this ‘mirror effect’ strengthens when the interview techniques discussed above are applied.
Van der Zee estimates that we as humans will not achieve to be flawless lie detectors. “But, with the combination of asking the rights questions, using evidence properly and using technology to interpret deceitful behaviour, I think we can get pretty far”, Van der Zee states.
Unmask a liar together?
Drawing on her expertise, Van der Zee collaborated with 'de Universiteit van Nederland' on a video applying the various detection techniques in a practice case of theft. Will you help unmask a liar?