For years, the theory has gained popularity in psychology that, when it comes to detecting signs that the person who is talking to us is lying, it is good to look at the expressions on their face. That is, taking into account the non-verbal language that is expressed through facial gestures is necessary to know whether someone is telling the truth or not.

The idea is that there are some signs, called facial microexpressions , that appear in different points of the face and that are so discreet, automatic and involuntary that reveal aspects about the person’s true intentions and motivations .

However, a recent study challenges this idea by pointing out that when it comes to detecting lies, the less you see of the other person’s face, the better. In other words, not paying attention to these visual signals can be useful when approaching the truth .

A Study Focusing on Lie Detection

This investigation was promoted by political issues: there are proposals to not allow witnesses in trials to wear clothing associated with the Muslim religion such as the niqab, which covers the entire head and exposes only the eyes of the woman.

In other words, it was wanted to see to what extent the grounds for prohibiting this were reasonable and based on objective facts relating to the way in which we can come to detect lies. To this end, a number of research teams from the University of Ontario and the University of Amsterdam coordinated their efforts to examine this issue in the laboratory.

How was the experiment conducted?

The study had two types of experiments in which a series of volunteers had to say whether several women who were acting as witnesses were telling the truth in a mock trial. To make it more realistic, each of the witnesses was shown a video showing a person stealing or not stealing a bag, so that each of them saw only one of two versions of what could happen: either it was stolen or it was not. In addition, they were told that they had to testify about the behavior they had seen and half of them were made to lie about what happened.

During the interrogation in the trial, some of the witnesses wore a hijab, which covers parts of the head but leaves the face uncovered; others wore the aforementioned niqab which only reveals the eyes of the wearer, and others wore clothes that did not cover the head. These trials were filmed and then shown to students in Canada, the United Kingdom and the Netherlands. They had to find out who was lying and who was telling the truth .

The results: the less you see, the better you know who is lying

The results, published in the journal Law and Human Behavior, were surprising. Interestingly, the students were more adept at detecting lies when it came to judging women with almost all their faces covered . In other words, it was easier to be right about what women thought when they wore hijab and, to a lesser extent, niqab. Women with no head covering were always “uncovered” to a lesser extent than others. In fact, they were often recognized as witnesses who lied by sheer luck, as the success rate did not come off significantly from 50%.

This not only went against the logic that we make better judgements the more information we have, but also indicated that negative stereotypes about Muslim women did not lead to more unfavourable judgements about them.

Possible explanations for this phenomenon

What do these results mean? One way to interpret them is to assume that the non-verbal signals we take into account (even if unconsciously) when judging the veracity of what we hear distract us more than anything else , making us reach false conclusions by relying on irrelevant information.

Therefore, the barriers that cover facial expressions force us to direct our attention to more reliable and relevant sources of information, such as the tone of voice, the frequency with which grammatical errors are made, voice tremor, etc. In fact, some of the students directly placed themselves in a position where they could not see the screen on which the video was shown when it was their turn to detect the possible lies of the veiled women, so as not to be distracted.