Forget shifty eyes or fidgety fingers, psychology research has shown that these supposed signs of lying are unreliable. Liars easily learn to make eye contact, and anxiety can make honest people squirm nervously.
A more useful foundation for lie-detection is the simple fact that lying is more cognitively demanding than telling the truth. False answers therefore usually take slightly longer than honest responses, especially when a suspect is burdened with an extra mental challenge, such as telling their story backwards.
However, a new study suggests that the cognitive demands of lying can be reduced with practice. Xiaoqing Hu and his team presented 48 participants with dates, place names and other information and asked them to indicate with one of two button presses whether the information was self-relevant or not. In real life this would be equivalent to a suspect posing as a different person. Instructed to lie, the participants took longer to respond than when they told the truth, consistent with the well-established idea that lying is cognitively demanding.
Next, a third of the participants were told about the reaction time difference and given extensive practice (360 trials) at lying more quickly about the self-relevance of information. The requirement to get faster was made explicit because past research found lying practice without such an instruction was ineffective. On retesting, the trained participants in the current study no longer took more time to answer dishonestly compared with telling the truth. “Deception is malleable and its performance index can be voluntarily controlled to be more automatic,” the researchers said.
Another group had no training but were told about the reaction time difference between lying and truth telling, and encouraged to answer faster when lying. They got faster at lying compared with a control group, but still they were speedier when being honest.
The researchers admitted that their sample size was small and a replication is needed with more participants. However, they said their results suggest that to be more realistic, lie-detection research based around the cognitive demands of lying should incorporate the effects of practice.
Hu, X., Chen, H., and Fu, G. (2012). A Repeated Lie Becomes a Truth? The Effect of Intentional Control and Training on Deception. Frontiers in Psychology, 3 DOI: 10.3389/fpsyg.2012.00488