A new method of lie detection shows that lie tellers who are made to multi-task while being interviewed are easier to spot. The extra brain power needed to concentrate on a secondary task other than lying was particularly challenging.
Professor Aldert Vriji from the University of Portsmouth designed an experiment to identify lie tellers. The 164 participants in the experiment were first asked to give their levels of support or opposition about various societal topics that were in the news. They were then given a truth or lie condition by chance and interviewed about the three topics that they felt most strongly about. Truth tellers were instructed to report their true opinions while lie tellers were instructed to lie about their opinions during the interviews.
For the secondary task, participants were given a seven-digit(数字) car number and instructed to recall it back to the interviewer. Half of them received additional instructions that if they could not remember the car number during the interview, they may be asked to write down their opinions after the interview.
Participants were given the opportunity to prepare themselves for the interview and were told it was important to come across as convincing as possible during the interviews — which was incentivized by being entered into a prize draw.
The results showed that lie tellers' stories sounded less reasonable and less clear than truth tellers' stories, particularly when lie tellers were given the secondary task and told that it was important.
"The pattern of result suggests that the introduction of secondary tasks in an interview could help lie detection but such tasks need to be introduced carefully. It seems that a secondary task will only be effective if lie tellers do not neglect it. This can be achieved by either telling interviewees that the secondary task is important, or by introducing one that cannot be neglected,'' said Professor Vriji.
