Cognitive theories on deception posit that lying requires more cognitive resources than telling the truth. In line with this idea, it has been demonstrated that deceptive responses are typically associated with increased response times and higher error rates compared to truthful responses. Although the cognitive cost of lying has been assumed to be resistant to practice, it has recently been shown that people who are trained to lie can reduce this cost. In the present study (n = 42), we further explored the effects of practice on one’s ability to lie by manipulating the proportions of lie and truth-trials in a Sheffield lie test across three phases: Baseline (50% lie, 50% truth), Training (frequent-lie group: 75% lie, 25% truth; control group: 50% lie, 50% truth; and frequent-truth group: 25% lie, 75% truth), and Test (50% lie, 50% truth). The results showed that lying became easier while participants were trained to lie more often and that lying became more difficult while participants were trained to tell the truth more often. Furthermore, these effects did carry over to the test phase, but only for the specific items that were used for the training manipulation. Hence, our study confirms that relatively little practice is enough to alter the cognitive cost of lying, although this effect does not persist over time for non-practiced items.

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We present the first study to map deception across the entire lifespan. Specifically, we investigated age-related difference in lying proficiency and lying frequency. A large community sample (n = 1005) aged between 6 and 77 were surveyed on their lying frequency, and performed a reaction-time (RT) based deception task to assess their lying proficiency. Consistent with the inverted U-shaped pattern of age-related changes in inhibitory control that we observed in a stop signal task, we found that lying proficiency improved during childhood (in accuracy, not RTs), excelled in young adulthood (in accuracy and RTs), and worsened throughout adulthood (in accuracy and RTs). Likewise, lying frequency increased in childhood, peaked in adolescence, and decreased during adulthood. In sum, we observed important age-related difference in deception that generally fit with the U-shaped pattern of age-related changes observed in inhibitory control. Theoretical and practical implications are discussed from a cognitive view of deception.

Cognitive models of deception focus on the conflict-inducing nature of the truth activation during lying. Here we tested the counterintuitive hypothesis that the truth can also serve a functional role in the act of lying. More specifically, we examined whether the construction of a lie can involve a two-step process, where the first step entails activating the truth, based upon which a lie response can be formulated in a second step. To investigate this hypothesis, we tried to capture the covert truth activation in a reaction-time based deception paradigm.Together with each question, we presented either the truth or lie response as distractors. If lying depends on the covert activation of the truth, deceptive responses would thus be facilitated by truth distractors relative to lie distractors. Our results indeed revealed such a "covert congruency" effect, both in errors and reaction times (Experiment 1). Moreover, stimulating participants to use the distractor information by increasing the proportion of truth distractor trials enlarged the "covert congruency" effects, and as such confirmed that the effects operate at a covert response level (Experiment 2). Our findings lend support to the idea that lying relies on a first step of truth telling, and call for a shift in theoretical thinking that highlights both the functional and interfering properties of the truth activation in the lying process.

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Lying takes more time than telling the truth. Because lying involves withholding the truth, this "lie effect" has been related to response inhibition. We investigated the response inhibition hypothesis of lying using the delta-plot method: A leveling-off of the standard increase of the lie effect with slower reaction times would be indicative of successful response inhibition. Participants performed a reaction-time task that required them to alternate between lying and truth telling in response to autobiographical questions. In two experiments, we found that the delta plot of the lie effect leveled off with longer response latencies, but only in a group of participants who had better inhibitory skills as indexed by relatively small lie effects. This finding supports the role of response inhibition in lying. We elaborate on repercussions for cognitive models of deception and the data analysis of reaction-time based lie tests.

This study validates previous laboratory research on alcohol and response inhibition in a realistic drinking environment, yet failed to find an effect of alcohol on lying. Implications of these findings and for the role of response inhibition in lying are discussed.

Lying is typically more cognitively demanding than truth telling. Yet, recent cognitive models of lying propose that lying can be just as easy as truth telling, depending on contextual factors. In line with this idea, research has shown that the cognitive cost of deception decreases when people frequently respond deceptively, while it increases when people rarely respond deceptively (i.e., the truth proportion effect). In the present study, we investigated two possible underlying mechanisms of the truth proportion effect. In Experiment 1 (N = 121), we controlled for the impact of switch costs by keeping the number of switches between deceptive and truthful responses constant. We found that people who often responded deceptively made fewer errors when responding deceptively than people who only occasionally responded deceptively, replicating the truth proportion effect. Thus, while the truth proportion effect in earlier studies may be partially driven by the cost of switching between truthful and deceptive responses, we still found evidence for the truth proportion effect while controlling for switch costs. In Experiment 2 (N = 68), we assessed whether the truth proportion effect is influenced by goal neglect. According to this view, the truth proportion effect should be reduced if participants are cued to maintain the task goals, while it should be larger when participants are allowed to neglect the task goals. In line with this hypothesis, we found a smaller truth proportion effect when participants were cued with the task goals compared to when they were not cued. This study shows that the truth proportion effect is influenced by goal neglect, implying that frequent deceptive responding strengthens the goal of responding deceptively. Our findings imply that the accuracy of lie detection tests could be increased by using a majority of truth-items (i.e., induce the truth proportion effect), and that the truth proportion effect should be maximized by (1) increasing the number of truth-lie task switches and (2) inducing goal neglect.