Mental Effort in Lying

There are many reasons why lying often requires more mental effort than truth-telling, particularly in an interview setting, and various sources provide empirical evidence that lying is indeed cognitively more demanding. If the reasons why lying requires mental effort are known, it is possible to predict under which circumstances lying is mentally taxing.

In an interview setting there are many factors that contribute to a liar's cognitive load. First, formulating the lie itself is cognitively taxing. Liars need to make up their stories while monitoring their fabrications so that they are plausible and adhere to everything the observer knows or might find out. In addition, liars must remember their earlier statements, and know what they told to whom, so that they can be consistent when retelling their story. Liars should also avoid making slips of the tongue, and should refrain from providing new leads to investigators.

Second, liars are typically less likely than truth-tellers to take their credibility for granted. There are at least two reasons for this. The stakes (that is, negative consequences of getting caught and positive consequences of getting away with the lie) are often higher for liars than for truth-tellers. Smugglers are probably keener to make an honest impression on customs officers than nonsmugglers because the negative consequences for having to open their suitcases are much higher for smugglers than for nonsmugglers. In addition, truth-tellers typically assume that their innocence shines through, which could be explained by the illusion of transparency, the belief that “one's inner feelings will manifest themselves on the outside,” and belief in a just world, the belief that people “will get what they deserve, and deserve what they get.” As such, liars will be more inclined than truth-tellers to monitor and control their demeanor so that they will appear honest to the lie detector.

Monitoring and controlling behavior is cognitively demanding. For example, the guilty suspect may experience powerful emotions (for example, fear, remorse, anger, or even excitement) that must be hidden or faked. Consider a woman publicly pleading for the safe return of her partner who, in reality, she murdered. She must monitor her body language and emotional expressions while [Page 663]keeping the details of the story straight. A high level of cognitive load accompanies high-stakes deception.

Third, because liars do not take credibility for granted, they may monitor the interviewer's reactions more carefully to assess whether they appear to be getting away with their lie. Carefully monitoring the interviewer also requires cognitive resources. Fourth, liars may be preoccupied by the task of reminding themselves to act and role-play, which requires extra cognitive effort. Fifth, deception requires a justification (that is, a psychological or material reason to lie), whereas truth-telling does not. Considering a justification is mentally taxing. Sixth, liars have to suppress the truth while they are lying and this is also cognitively demanding. Finally, while the truth often comes to mind automatically, activation of the lie is more intentional and deliberate, and thus requires mental effort.

Lying is not always more cognitively demanding than truth-telling. For example, in daily life situations it is often easier to lie (“I like the present you gave me”), than to tell the truth (“I am really disappointed with this present”). The seven reasons given as to why lying is more cognitively demanding can provide insight into when it is more cognitively demanding—that is, lying is more cognitively demanding to the degree that these seven principles are in effect. For at least some of these principles to be fulfilled, two elements are required.

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