Friends of the Nonverbal Communication Blog, this week we present the paper “Looking guilty: Handcuffing suspects influences judgements of deception”, by Zloteanu, M.; Salman, N. L.; Krumhuber, E. G. and Richardson, D. C. (2022), in which authors carry out a study with police officers and civilian citizens to know how does the fact that suspects are handcuffed or not to the interviewers’ judgment.

Detecting deception may be crucial in forensic investigation contexts, where the judge’s and/or jury’s decision may depend on the credibility of victim, witness or suspect’s testimony. 

However, truthfulness trials are a major challenge, especially for those whose decision is the one that will condemn or acquit a defendant. 

As we have discussed several times before, people tend to be bad at detecting lies. Our judgment is biased toward overestimating the honesty of others and relying too much on ourselves. 

Given the enormous importance of these judgments in the legal context, it is vital to examine the role of situational factors in this process. 

For this reason, authors decided to use an experimental scenario in which they simulated a real interrogation. They handcuffed some people who were to play the role of suspects, and examined how this might affect the truthfulness judgments of those who had to decide whether the suspect was lying or not.

Before explaining the study and the conclusions, the authors give a brief review of the existing literature. 

The reality is that those who make these truthfulness judgments (hereafter we will call them “judges”) do so with poor quality. This is something that has been attributed, in part, to the lack of reliable behavioral cues that differentiate liars from truth-tellers. 

For example, people believe that liars touch themselves more, move more, tend to look away, and are generally anxious and nervous. However, these beliefs rarely match reality. 

In fact, one of the reasons the authors chose this topic for their study was that, according to studies from 2006, 2007 and 2004, liars tend to make fewer hand and finger movements and use fewer illustrative gestures compared to those who tell the truth. Therefore, the idea of restricting the movements of “suspects” in this study may have an impact on the discriminability of liars and truth-tellers. 

That is, in this case, the reality contrasted by different studies is contrary to popular belief.

On the other hand, the literature on deception detection has largely overlooked the impact of situational factors (external elements that influence the process) on liars and truth-tellers. That is, the situation in which they find themselves can affect their behavior. 

For example, manipulating people’s clothing can affect the judges’ empathy for the suspect. And wearing glasses can increase the judge’s perception of the suspect’s intelligence, honesty, and trustworthiness.

Authors decided to include police officers in this study because research with police professionals is often scarce in the field of deception detection. 

The available data suggest that police officers show similar performance to other citizens regarding this matter. This may be due to police officers relying on signals to determine deception that are not entirely correct. 

In the study at hand, a number of 83 people were obtained who would take the role of “judges”; of these, 23 were police officers. The suspects were 19 persons, who were randomly distributed into two groups: handcuffed and uncuffed persons. 

Prior to interrogation, the suspects completed four items from a questionnaire used to measure individual differences in Machiavellianism. Subsequently, two of these four responses were modified so that the suspect had two honest and two dishonest responses.

Afterwards, they were allowed to read the modified responses and were instructed to justify them to the interviewer when the time came. 

As expected by the authors, it appears that the handcuff manipulation affected both police officers and those who were civilian citizens. Statements made by handcuffed suspects were more difficult to classify for both groups. That is, the probability that a handcuffed suspect would be misclassified in terms of the truthfulness of his or her statement was nearly 65%.

One result that the authors found troubling was that police officers showed greater confidence in their decisions without being more accurate than the civilian citizen group.

Overall, both police and non-police officers performed worse on their task when the suspect was handcuffed, supporting the authors’ assertions that situational factors can negatively affect.

That is, the results illustrate that situational elements can affect people’s perception and judgment. Reducing the impact of these factors could improve forensic practices and, more importantly, deception detection procedures, while reducing the risk of potential miscarriages of justice. 

Authors recommend that future research along these lines should be devoted to studying in more depth how exactly it affects whether or not the suspect is handcuffed when it comes to making truthfulness judgments. They also note as very interesting a focus on the suspect’s ability to gesticulate.

If you want to know more about nonverbal behavior and how it affects personal relationships, visit our Master of Science in Nonverbal and Deceptive Behavior, which you can take in English or Spanish, with special grants for readers of the Nonverbal Communication Blog.


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