The key to spotting a liar

Reading time: 2 minutes – Seen on BBC Science Focus

A quiver in the voice, a confused look, a story that is a bit far-fetched… we are sometimes convinced that the person in front of us is lying. Other times, we are deceived without even realizing it. So how do you spot a lie? Is there a miracle method that will work every time? To find out whether it’s possible to accurately grill a bullshitter, BBC Science Focus interviewed the authors of a study that compiled a variety of lie detection techniques.

In this work, published on December 14, 2023, Timothy Luke at the University of Gothenburg in Sweden and his colleagues carefully examined research published by fifty international experts over the past five years on lie detection.

According to the myth, a liar avoids eye contact with the person he is talking to. It would be so easy if that were the case! Unfortunately, a study by Timothy Luke showed that 82% of experts agreed that liars are no more likely to avoid eye contact than others. Pär-Anders Granhag, a psychologist and co-author of the study, regrets it, but a bleak look. “Diagnosis not indicative of fraud”. Similarly, 70% of experts say that liars do not seem more nervous than innocent people.

Pay attention to speech

Aldert Vrij, an expert on the psychology of lying, suggests that the key to detecting a lie is not in the non-verbal, but rather in the spoken word. Instead of continuing to experiment with new technologies based on neuroimaging, which is controversial even in research on lie detection, Timothy Luke explains that we should pay more attention to what the person is saying. More specifically, in 72% of cases, liars are able to provide fewer details than innocent people.

When asked for additional details with their back against the wall, the liar complicates their speech. This then becomes more muddled and disjointed, even inconsistent if the liar is not good. For the study’s authors, these could be considered verbal cues “reliable”

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As a result, research by Timothy Luke and his team shows that the most effective way to uncover a lie through words is to reveal the evidence piecemeal. From there, all that’s left is to carefully observe the interlocutor’s response and see how they adapt to each new element you reveal. If the person is forced to change their story along the way, then you’re probably onto something.

Every lie is unique

The study also shows one thing: if a universal index of lying is so hard to find, it may simply be because it doesn’t exist.

Over the past century, researchers have almost exclusively adopted the so-called nomothetic approach. This means that they were looking for “LUniversal Law” Cheating, signs that will appear in everyone. But above all, research shows that everyone lies differently. The signs are unique to each person: one person may scratch their nose, another may cough more, a third may blush.

A 2022 scientific article published a personalized approach with the creation of a personal lie detector for the individual. Donald Trump was the lucky beneficiary of this technique. By analyzing the tweets of the former US President, the detector was able to distinguish whether the facts stated in the tweet were false in 74% of the cases. However, this example also illustrates that catching a liar is not enough to prevent them from reoffending.