How can you tell someone is lying? Often there are tell-tale mannerisms or blushing, aboding eye contact and the like. However, there are many who are adept at hiding their ability to spout falsehoods. This becomes more problematic in cases of life and death.
Exposing liars by distraction is the basis of a new method of lie detection. The method shows that lie tellers who are made to multi-task while being interviewed are easier to spot.
The University of Portsmouth research draws more on the psychological than the physical, in order to weed out serial liars. At the heart of this is the fact that lying during interviews takes up more cognitive energy, compared with telling the truth.
The new research builds on this and establishes that investigators who used this finding to their advantage by asking a suspect to carry out an additional, secondary, task while being questioned are more likely to expose lie tellers.
This is because the extra brain power needed to concentrate on a secondary task (other than lying) becomes far more challenging for lie tellers.
This was demonstrated through study. For the experiment, a secondary task was selected. The secondary task used in this experiment was to recall a seven-digit car registration number. However, the reaction to this secondary task was only found to be effective if lie tellers were told that it was important. Then the process of dividing attention between formulating a statement and a secondary task, provided sufficient behavioural differences for researchers to successfully pick liars and non-liars out from a test group.
To show this, a study was run using 164 participants. The subjects were first asked to give their levels of support or opposition about various societal topics that were in the news. They were then randomly allocated to a truth or lie condition and interviewed about the three topics that they felt most strongly about. Truth tellers were instructed to report their true opinions whereas lie tellers were instructed to lie about their opinions during the interviews.
Those doing the secondary task were given a seven-digit car registration number and instructed to recall it back to the interviewer. Half of them received additional instructions that if they could not remember the car registration 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 (this was incentivised by the participants believing they were being entered into a prize draw).
The detection was successful because the process also reduces the for opportunity for liars to think what to say, and thus engage in behaviours to avoid detection. From this, in situations, the opportunity to think becomes less, truths often sound more plausible than lies.
The results revealed that lie tellers’ stories sounded less plausible and less clear than truth tellers’ stories, particularly when lie tellers were given the secondary task and told that it was important.
The research appears in International Journal of Psychology and Behaviour Analysis, titled “The Effects of a Secondary Task on True and False Opinion Statement.”