The current study undertook a first step to investigate the influence of alcohol on the detection of concealed information. To that means, we used a correlational field design, in which participants were recruited and tested in a night club in which alcohol consumption was voluntary.

The first notable result of our study is the observation of large RT CIT-effects obtained in a high noise environment with part of the participants even being intoxicated (d = 1.50). Other research has already shown that RT-CITs can be successfully administered via the internet25 and our results strengthen the conclusion that robust CIT effects can be obtained even when testing conditions differ from typical laboratory settings and when participants may not be fully concentrated. The second notable result is the correlation between RT CIT-effect and BAC. The more intoxicated participants were, the larger the RT difference between their “no” responses to their own identity compared to their “no” responses to neutral stimuli. This result is in contrast to the idea that alcohol reduces attention and processing of the probes and strengthens the idea that the time-consuming process of inhibiting the truthful response contributes to the RT-CIT effect. Of course, the influence of alcohol on response inhibition is only one explanation for the observed pattern. Other theoretical explanations are possible, with an example being that instead of purely reducing attention, alcohol may rather cause a shift towards a less focused, yet more diffuse and distributed attention, which may in the CIT result in decreased performance on targets, but at the same time facilitate processing of probe items26. Further analyses on the performance on target trials, that primarily served to investigate a potential more general effect of alcohol on working memory capacity and action selection do, however, not support such an explanation. Those analyses revealed no significant correlations between alcohol consumption and the performance on target trials (using the performance on neutral trials as baseline). Note that on the basis of these results, we can of course not rule out that correlations may turn significant with larger power (especially with the low p-value in the correlation in the error rate). However, those results do point in the direction that such correlations and thereby general effects of alcohol on working memory capacity and action selection may not be as strong as the effects of alcohol on response inhibition (which is needed for a correct performance on probes and not on targets). Unfortunately, our field design did not allow for a random allocation of BACs to participants, and due to strict time constraints, we could not asses potentially confounding variables such as impulsivity or general drinking behavior. Importantly, impulsivity did not correlate with acute alcohol intoxication in a similar field design13 and accumulating evidence suggests that it does represent an inhibition component that is different from the type of motor inhibition that is hypothesized to underlie RT-CIT effects27,28,29,30. In contrast, habitual alcohol intoxication has been shown to correlate with acute alcohol intoxication in a similar field design13 and also with response inhibition capacities31,32. We therefore cannot exclude that habitual alcohol use may have contributed to (but most likely does not fully explain, see ref.13) the increase in the RT-CIT effect, yet this does not necessarily invalidate the conclusion that response inhibition processes are driving RT CIT-effects. It would be interesting for further research to investigate whether this conclusion also holds for other types of concealed information. In the current experiment, we used very salient and deeply encoded identity information. Although there are situations in which such identity information is the information that investigators want to reveal (e.g., in cases where the identity of a suspect is unknown or an examinee is suspected of hiding his/her actual identity), such cases do not represent the most typical scenario for CIT use. More frequent situations in the field concern settings where involvement in a crime should be determined by assessing knowledge of crime details in a CIT. Research investigating the effects of alcohol on attentional processes suggests that such effects may be mediated by effects of alcohol on working memory33,34. It would therefore be of theoretical as well as applied interest to investigate how acute alcohol intoxication would modulate attention to less-deeply encoded information (e.g., information that has been incidentally acquired during a [mock] crime). Under such circumstances, alcohol may have more pronounced negative effects on memory and recall performance, which may, in turn, decrease response costs for critical information.

Further research should also assess potential dissociations between different concealed information measures (e.g., RTs and autonomic response measures). Interestingly, whereas alcohol has been found to impair attention measured in behavioral tasks or attention-related event-related potentials, it has also been shown to increase autonomic indices of the orienting response35. This would be especially interesting considering that recent research suggests a stronger influence of response inhibition on behavioral and neural measures of concealed information compared to autonomic measures16.

The current study provides first evidence for the impact of alcohol on the detection of concealed information from behavioral responses. This is not only interesting from the above mentioned theoretical perspective, but may also be relevant in applied contexts in which suspects or eye-witnesses may incidentally be intoxicated during first interrogations or when potential suspects may secretly use alcohol in the hope to “defeat” the test. If such alcohol use remains undetected or when CIT examinations cannot be postponed (e.g., in cases of terroristic threats or abductions), the current results indicate that the test is still valid and yields even larger RT CIT-effects. It should be explicitly noted though that we do not suggest to conclude from our results that alcohol should be given to examinees in order to increase CIT-effects. Aside from the fact that the effect of alcohol on innocent examinees is still unknown, ethical considerations definitely prevent such practice.

A few limitations of the current study should be mentioned. First, our results are in contrast with data from Bradley and Ainsworth (1984)7, who did not find effects of alcohol intoxication on autonomic responses in the CIT. Although these contrasting results may be explained by the considerably smaller sample size in the study of Bradley and Ainsworth (1984; n = 8 in the group that was intoxicated during the test) and by the aforementioned potential differences between behavioral and physiological measures, further research is necessary to explore those possibilities. Second, with n = 42, also the sample size of our study was restricted. Although there was a relatively high number of participants with zero BAC, the remaining BAC levels showed a sufficient variability across a relatively large range, indicating that the current sample was appropriate for estimating correlations with CIT responses. A replication of the study, preferably by another research group, is, however, indispensable to gain more reliable information in the existence and the size of the true effect. Third, as mentioned above, our field design did not allow for a random allocation of participants to the experimental condition (i.e., BACs). We hope our findings encourage future research in more controlled laboratory settings using random allocations of participants to either an alcohol or a placebo group, which could shed light on the question which of the highly entangled factors like acute alcohol intoxication, habitual alcohol use or impulsivity traits most strongly affects CIT performance.

Taken together, the current results demonstrate that robust CIT effects can be obtained even when testing conditions differ from typical laboratory settings. The positive correlation of RT-CIT effects with BAC furthermore suggests that response inhibition contributes to the RT-CIT effect.