Lying, Costs of

Cost of Lying as Cognitive Load

Many psychology studies suggest that lying requires greater mental effort than telling the truth. Compared with producing truthful speech, deceptive speech generates characteristic behavioral cues that indicate the increased cognitive effort: longer response latencies; more speech hesitations; pupil dilations; less hand, facial, and eye movements; gaze aversion; and higher skin conductance levels. The increased cognitive effort is mainly relevant to two components of the lie-production process.

The first component of the lie production process is to construct a false message. The liar must handle automatically activated social-cognitive and contextual knowledge. They must suppress harmful (but true) elements of the message, while producing plausible (though false) alternative elements, so that their false message aligns with the remaining truthful elements as well as the target's knowledge.

The second component of the process is to monitor one's outward behavior and the target's reaction, to assess whether he or she is successful in the lie. The liar can then adjust his behavior based on his assessment, avoiding the target's suspicion.

These two components of lie production are deeply relevant to the executive functions—the effortful, deliberative, and conscious cognitive functions, such as attention, metacognition, working memory, and inhibition. These same functions play a central role in planning, decision making, problem solving and other complex cognitive tasks.

Some recent studies suggest that making use of the cognitive load of lying can help in the development of lie detection tools. Albert Vrij and his colleagues conducted an experiment in which participants reported their stories in reverse chronological order. Liars showed less plausible and less detailed responses than truth-tellers. In another experiment, Jeff Walczyk and his colleagues tracked eye movements and other cognitive cues of participants. Liars showed longer response time, less consistent response, and fewer eye movements.

These studies demonstrate that when additional cognitive load is imposed (for example, by reverse-chronological-order report or by eye-gazing), liars get too tired to maintain their “truthful” appearance and give away behavioral cues, such as less plausible and less detailed reports, longer response time, or fewer eye movements. These behaviors are exclusive to people who are lying; truth-tellers do not exhibit these behaviors because they are not busy with the extra cognitive effort involved in lying.

However, other researchers suggest that telling the truth can be cognitively expensive too. In Steven McCornack's information manipulation theory 2, the information (whether truthful or false) that efficiently resolves the discrepancy between current-state and desired end-state is activated more and is more easily fed to the speech realization system. In fact, if the truth doesn't resolve the discrepancy, the truthful information would be rather suppressed and would require a greater cognitive load to realize into speech. In other words, it is easier to lie in such a situation.

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