Friends of the Nonverbal Communication Blog, this week we present the paper “Catching a Liar Through Facial Expression of Fear”, by Shen, X.; Fan, G.; Niu, C. and Zhencai, C. (2021), in which authors investigate whether it is possible to distinguish between truth and lie paying attention to the facial expressions of fear.

One of the main unknowns of non-verbal language is whether it can be differentiated between the lie and the truth based on observable nonverbal behaviors.

Almost all the expert investigators in the field of deception detection agree that there is no “Pinocchio nose” that can serve as a key and simple identifier of the lie.

However, there is also the so-called “leak theory” which holds that if the lies occur in high-risk situations (in these cases, both rewards and punishments are important) this context can lead to a leak of the lie, which would result in physiological or behavioral changes.

Specifically, it would be the observable emotional facial expressions (micro and macro expressions) that could, to some extent, determine who is lying and who is telling the truth.

However, there is a debate among the scientific community about this matter. Some researchers argue that facial microexpressions are useful for this purpose, but others believe that it is not the best way to catch liars.

Although it can be difficult to detect liars based on micro-expressions, there are some behavioral cues that, to some extent, can be helpful in differentiating between a lie and the truth.

For example, pupil dilation and tone, have been shown to be closely related to lying.

The leak theory also says that, when lying, and especially in high-risk situations, people would be afraid that their lies would be detected and therefore this emotion of fear could leak out and appear.

Some experts argue that emotions of fear can also appear when telling the truth, however, whoever tells the truth does not need to try as hard to suppress fear as liars do.

Therefore, in theory, the degree of repression by the liars would presumably be greater, so that the duration of their facial expressions of fear would be shorter.

In addition to duration, other characteristics could vary between genuine and fake facial expressions, such as symmetry. In fact, Ekman has already shown that genuine smiles have more symmetry compared to deliberate and faked ones.

Similarly, leaked emotional facial expressions when you feel scared when lying, and other expressions too, could show different degrees of symmetry.

This is a subject that for a few years has been studied by experts through experiments in which, in the most cases, the human eye is used to judge.

However, compared to humans, some previous work with automatic and technological learning achieved more than 70% accuracy in detecting deception. Therefore, the authors choose this method to carry out the research.

Why? Because asking people to discover signs of deception is a difficult task, as we may not be able to perceive the subtle differences between the expressions. And automated methods have proven to be just as or even more successful.

Authors used 32 video clips from 16 different people, telling the truth in half of them and lying in the other half. The videos were part of a high-stakes television show, in which half a million dollars is at stake. Participants can win if they tell the truth. To find out whether they lie, a polygraph is used.

The obtained results with automatic detection techniques, indicated that emotional facial expressions of fear could differentiate the lie from the truth in high-risk situations.

Comparisons showed significant differences between lying and telling the truth in AU20 ​​(unit of action consisting of stretching the lips horizontally back) values.

The results also confirmed the hypothesis that the duration of fear action units when lying, is shorter than when telling the truth.

And, on the other hand, differences were also found in terms of symmetry between lying and telling the truth. That is, the genuine expressions would be more symmetrical than the false ones.

We have already commented that those who tell the truth also experience fear. However, the dynamics of fear experienced is very different from that of liars. Therefore, this emotion could be considered “a hot spot” to differentiate between truth and falsehood.

A limitation of the study may be the number of participants, which reaches 16 people and can be considered small. For this reason, the authors prefer to call this work “preliminary exploration”.

That is, they consider that the possibility of using fear as a key aspect to differentiate between truth and lies should continue to be explored, since the results of their study are promising.


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