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Lie detection

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Friends of the Nonverbal Communication Blog, this week we present the paper “No evidence that instructions to ignore nonverbal cues improve deception detection accuracy”, by Bogaard, G. and Meijer, E. H. (2022), in which authors carry out a series of experiments to know whether, when somebody receives the order of ignoring the nonverbal behavior of other person, effectively, he/she does, and pays more attention to verbal cues, making it easy the deception detection process, and doing it more effectively. 

When people are asked what they look for in a person when trying to unmask and uncover their lies, most of them answer that they pay attention to nonverbal signs such as gaze aversion or general nervousness.

People believe that such nonverbal signals are the most difficult to suppress and control, more so than verbal signals, therefore, they are very useful in detecting lies. 

This belief that nonverbal cues are a foolproof diagnostic method for deception diagnoses is common in most countries. Even dedicated experts such as police officers, correctional officers, probation officers, prosecutors or judges strongly believe it on many occasions. 

However, this belief is at odds with empirical research, which shows that the relationship between nonverbal cues and deception is actually weaker than we think. 

Knowledge of nonverbal communication cues is useful in many areas, but empirical evidence has shown that paying attention to them alone is not the most reliable method of catching a liar.

Judges and prosecutors are often warned not to pay attention to whether a witness looks away, moves, is nervous, or speaks too fast, as these signals may lead us to errors. 

Even police departments around the world, such as the Dutch police, expressly advise officers that stereotypical nonverbal cues do not indicate deception and therefore should not be used to make credibility judgments. 

Based on legal research, there is reason to be skeptical about the effectiveness of ignoring instructions when making a judgment. Authors point out that when evidence (that is, evident nonverbal cues) makes a significant impression on jurors, it is very difficult to eliminate the impact, even if they have been expressly instructed to please disregard a specific element. 

Empirical research shows that verbal cues are indeed more diagnostic for lying than nonverbal cues. Liars are generally less forthcoming, tell stories less convincingly and plausibly, and include fewer verifiable details. And therefore, people who rely more on these types of cues when making deception judgments outperform those who rely solely on nonverbal cues in accuracy. 

In addition, having training in what verbal behaviors we should pay attention to, is positively correlated with accuracy in lie detection. 

Thus, being instructed to pay attention to verbal cues is likely to result in increased accuracy in lie diagnosis. 

To test this, authors conducted three experiments that had more or less the same basis. Participants were asked to watch videos in which people were interviewed and told about events in their lives. Some of these stories were lies and others were true. The participants were divided into several groups, each with a condition: one group received no instructions at all, another group was instructed to ignore the nonverbal cues, and the last group was instructed to pay attention only to the verbal cues in addition to ignoring the nonverbal cues. 

The results show that giving instructions to ignore nonverbal cues is far from sufficient to prevent people from being influenced by them, and thus far from improving deception detection. 

In one of the three experiments it seems to have improved the latter point, however, not in a statistically significant way. 

Ignoring nonverbal cues seems to be a very complicated task, possibly because they play a vital role in everyday social interaction. This reliance on nonverbal cues is called visual bias.

It is suggested that future research should devote efforts to investigate this issue, as relying too much on nonverbal cues may lead us to make wrong decisions in diagnoses of truthfulness and deception, which, depending on the context, may go hand in hand with very negative consequences that, with research, could be prevented. 

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