There is widespread belief in the legal system that alcohol impairs witness testimony.Nevertheless, most laboratory studies examining the effects of alcohol on witness testimony suggest that alcohol may affect the number of correct but not incorrect details recalled. However, it is difficult to draw conclusions because sample sizes, testing paradigms, and recall measures vary between individual studies. We conducted a metaanalysis to address this issue. We found alcohol intoxication had a significant and moderate sized effect on the number of correct details recalled (g = 0.40). The effect of alcohol on the number of incorrect details recalled was not significant. Further, the effect of alcohol on the recall of correct details was significantly moderated by multiple factors like intoxication level, the retention interval length between encoding and recall, and the types of questions asked (i.e., free recall vs. cued recall). We discuss the applied implications of the results.

RationaleCannabis use is widespread and has previously been associated with memory impairments. However, the role of cannabis in relation to false memory production, i.e., memories of events that were not experienced, is less well-understood.ObjectiveThe aim of the current field study was to examine the impact of cannabis use on false memory production.MethodsThe Deese/Roediger-McDermott (DRM) paradigm was used to induce false memories. In this paradigm, participants study word lists that are associatively related to a non-presented word, termed the critical lure. In a later memory test, true recognition rates and false alarm rates toward critical lures and unrelated items are assessed. Memory performance was compared between three groups: regular cannabis consumers who were acutely intoxicated (n = 53), regular cannabis consumers who were sober (n = 50), and cannabis-naïve controls (n = 53). The participants were approached in Dutch coffee shops (cannabis outlets) and cafes and asked to participate in our study. After collecting general information on their cannabis use, they were subjected to the DRM procedure.ResultsAlthough false memory rates for critical lures did not statistically differ between groups, both intoxicated and sober cannabis consumers falsely recognized more unrelated items than control participants. Also, individuals without a history of cannabis use demonstrated higher memory accuracy compared with the intoxicated group.ConclusionIt is concluded that cannabis intoxication and history of cannabis use induce a liberal response criterion for newly presented words for which the level of association with previously learned words is low and uncertainty is high.

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With the growing global acceptance of cannabis and its widespread use by eyewitnesses and suspects in legal cases, understanding the popular drug’s ramifications for memory is a pressing need. In a double-blind, randomized, placebo-controlled trial, we examined the acute and delayed effects of Δ9-tetrahydrocannabinol (THC) intoxication on susceptibility to false memory in 64 healthy volunteers. Memory was tested immediately (encoding and retrieval under drug influence) and 1 wk later (retrieval sober). We used three different methods (associative word lists and two misinformation tasks using virtual reality). Across all methods, we found evidence for enhanced false-memory effects in intoxicated participants. Specifically, intoxicated participants showed higher false recognition in the associative word-list task both at immediate and delayed test than controls. This yes bias became increasingly strong with decreasing levels of association between studied and test items. In a misinformation task, intoxicated participants were more susceptible to false-memory creation using a virtual-reality eyewitness scenario and virtual-reality perpetrator scenario. False-memory effects were mostly restricted to the acute-intoxication phase. Cannabis seems to increase false-memory proneness, with decreasing strength of association between an event and a test item, as assessed by different false-memory paradigms. Our findings have implications for how and when the police should interview suspects and eyewitnesses.

Police perceptions of eyewitness impairment due to alcohol and other drug use: a cross-cultural comparison.Victims, witnesses, and suspects of crime are frequently intoxicated by Alcohol or Other Drugs (AOD) during the event. How intoxication is perceived by investigating officers, and the manner in which this is handled during interview procedures, can affect the quality of information obtained and therefore investigative outcomes. Various factors are likely to contribute to how intoxication is handled during the investigation of a crime, including standard procedures, familiarity with the effects of different substances, and cultural attitudes. While findings with respect to the effect of different substances on memory are still emerging, it is important to investigate whether police beliefs are consistent with available evidence. In this study, Australian and Indonesian police officers were surveyed about their perceptions of memory accuracy and credibility of victims and witnesses intoxicated with various substances (e.g., alcohol, cannabis, amphetamines, and opioids). A higher proportion of Australian police identified larger negative memory effects associated with alcohol intoxication. At the same time, Indonesian police were found to be more likely to report that intoxication with alcohol would make a victim or witness less credible.With regard to timing, across multiple substances, larger proportions of Australian police reported believing that information obtained from witnesses that were still intoxicated would be more accurate than if interviewed after they became sober. It is concluded that, in order to rectify misconceptions about the impact of AOD intoxication on memory and improve investigative practices, both Australian and Indonesian police would benefit from additional training on the effects of intoxication.

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Memory experts are sometimes asked to evaluate the validity of accounts of witnesses, victims, or suspects. In some of these cases, they are asked what effect alcohol has on the validity of such accounts. In this article, we offer a guide on what expert witnesses can reliably say about how alcohol affects memory. We do so by resorting to effect sizes from previous studies and meta-analytic work, and address this novel question: Are these effect sizes meaningful in legal cases? More specifically, we argue that any determination of whether individual studies about alcohol and memory are practically relevant for legal cases, scientists must focus on the smallest effect size of interest. We make the case that a decrease or increase of only 1 detail, especially an incorrect detail, should be regarded as the smallest effect size of interest in this line of research. In line with this idea, we show that effect sizes in the alcohol and memory literature are often larger than this smallest effect size of interest. This finding is important because it implies that alcohol often exerts a practically relevant and meaningful detrimental effect on the reporting of both correct and incorrect details, which in turn negatively affects the validity of witness testimony.

Alcohol use is frequently involved in crime, making it crucial to understand the role of alcohol in facial recognition to maximize correct perpetrator identifications. Although the majority of the alcohol and face recognition research has investigated recognition with retrospective confidence judgments, we examined the effects of alcohol intoxication on face recognition with prospective metacognitive judgments. Participants (N = 54 university students without a history of hazardous alcohol/substance use) consumed either alcohol (mean breath alcohol concentration of 0.06 at pretest and 0.07 at post-test) or a non-alcoholic placebo drink. Participants then studied unfamiliar male and female faces and made judgments of learning (JOLs) for each face (i.e., predicted the likelihood of recognizing that face on a future memory test). After a brief distractor task, participants completed an old-new recognition test on which they attempted to distinguish the studied faces from new faces. It was found that the alcohol manipulation had minimal effect on face recognition performance or judgments of learning. Our results suggest that theory-based cues about the effects of alcohol might play a greater role in retrospective judgments than prospective judgments. Although not a primary focus of the study, face recognition was better for male faces than female faces, and this occurred for both female and male participants.Limitations and implications of the research are discussed.