Lying requires more cognitive energy than telling the truth. Working with this fact, researchers have found that the extra brainpower needed to concentrate on secondary tasks when being interviewed can expose liars. The corresponding study was published by the University of Portsmouth.
"In the last 15 years we have shown that lies can be detected by outsmarting lie tellers. We demonstrated that this can be done by forcing lie tellers to divide their attention between formulating a statement and a secondary task,” said Professor Aldert Vrij, from the Department of Psychology at the University of Portsmouth, one of the study’s authors.
"Our research has shown that truths and lies can sound equally plausible as long as lie tellers are given a good opportunity to think what to say. When the opportunity to think becomes less, truths often sound more plausible than lies. Lies sounded less plausible than truths in our experiment, particularly when the interviewees also had to carry out a secondary task and were told that this task was important."
For the study, the researchers recruited 164 participants. They were first asked to indicate their level of support or opposition to various societal topics. They were then randomly given a truth or lie position and interviewed on the three topics they felt most strongly about. Whereas truth-tellers were told to report their real opinions, lie-tellers were told to make their opinions up during interviews.
Two-thirds of the participants were also instructed to remember a seven-digit car registration number and recall it back to the interviewer. To incentivize memorization of this number, the researchers told half of these people that if they could not remember it during the interview, they may need to write their opinions afterward.
In the end, the researchers found that the lie-tellers’ stories sounded less plausible and less clear than the truth-tellers- and that this was especially true for those asked to remember the seven-digit number and potentially write their opinions afterward.
The researchers say their findings suggest that secondary tasks during interviews could facilitate lie detection as long as the interviewees don’t neglect the tasks. The researchers said that this could be achieved either by informing them that the task is important or by introducing a task that cannot be neglected, such as driving a car simulator or gripping an object.