Exposing Distracted Liars – Science Reveals New Lie Detection Method

According to new research, it is easier to spot that someone is lying if the suspect is made to perform a secondary task during their interrogation.

In one experiment, investigators who asked a suspect to perform an additional, secondary task while being interrogated were more likely to expose the liars.

A new method of detecting lies shows that lie tellers who are asked to multi-task during an interview are easier to detect.

It is well established that lying in interviews consumes more cognitive energy than telling the truth. Now a new study of University of Portsmouth found that investigators who used this knowledge to their advantage by asking a suspect to perform an additional, secondary task while being interrogated were more likely to expose liars. The extra brain power needed to focus on a secondary task (other than lying) was particularly difficult for lietellers.

In this experiment, the secondary task used was to recall a seven-digit car registration number. The secondary task was found to be effective only if the lietellers were led to believe it was important.

“Our research has shown that truths and lies can seem equally plausible as long as the lietellers have a good opportunity to think through what to say. When the opportunity to think becomes less, the truths often seem more plausible than the lies.

Professor Aldert Vrij, Professor of Psychology

Professor Aldert Vrij, from the Department of Psychology at the University of Portsmouth, who designed the experiment, said: “Over the past 15 years we have shown that lies can be detected by outwitting lie tellers. We have demonstrated that this can be done by forcing lietellers to divide their attention between making a statement and a secondary task.

“Our research has shown that truths and lies can seem equally plausible as long as the lietellers have a good opportunity to think through what to say. When the opportunity to think becomes less, the truths often seem more plausible than the lies. Lies seemed less plausible than truths in our experiment, especially when respondents also had to perform a secondary task and were told that this task was important.

The 164 participants in the experiment were first asked to give their level of support or opposition on various societal issues that were in the news. They were then randomly assigned to a truth or lie condition and asked about the three topics that mattered most to them. Truth tellers were instructed to report their true opinions while lie tellers were instructed to lie about their opinions during interviews.

“The pattern of results suggests that introducing secondary tasks into an interview might make it easier to detect lies, but these tasks should be introduced with care.”

Professor Aldert Vrij, Professor of Psychology

Those who performed the secondary task received a seven-digit registration number and had to remind the interviewer. Half of them received additional instructions that if they could not remember the car’s registration number during the interview, they could be asked to write down their opinions after the interview.

Participants were given the opportunity to prepare for the interview and were told that it was important to present themselves as convincingly as possible during interviews – which was prompted to enter a lottery.

The results revealed that the lietellers’ stories seemed less plausible and less clear than the truthtellers’ stories, especially when the lietellers were given the secondary task and told it was important.

Professor Vrij said: ‘The pattern of results suggests that introducing secondary tasks into an interview could help detect lies, but these tasks should be introduced with care. It seems that a secondary task will only be effective if the tellers of lies do not neglect it. This can be achieved either by telling respondents that the secondary task is important, as demonstrated in this experiment, or by introducing a secondary task that cannot be overlooked (such as grasping an object, holding an object in the air, or driving a car simulator). Secondary tasks that do not meet these criteria are unlikely to facilitate lie detection.

The research was published in the International Journal of Psychology and Behavior Analysis.

Reference: “The Effects of a Secondary Task on True and False Opinion Statements” by Aldert Vrij, Haneen Deeb, Sharon Leal and Ronald P. Fisher, March 28, 2022, International Journal of Psychology and Behavior Analysis.
DOI: 10.15344/2455-3867/2022/185

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