Effects of cannabis on eyewitness memory: A field study

Abstract

SummaryEyewitnesses to crimes are regularly under the influence of drugs, such as cannabis. Yet there is very little research on how the use of cannabis affects eyewitness memory. In the present study, we assessed the effects of cannabis on eyewitness recall and lineup identification performance in a field setting. One hundred twenty visitors of coffee shops in Amsterdam viewed a videotaped criminal event, were interviewed about the event, and viewed a target‐present or target‐absent lineup. Witnesses under the influence of cannabis remembered significantly fewer correct details about the witnessed event than did sober witnesses, with no difference in incorrect recall. Cannabis use was not significantly associated with lineup identification performance, but intoxicated witnesses were significantly better at judging whether their lineup identification was accurate. Theoretical and practical implications of the findings are discussed.

False memory formation in cannabis users: a field study

“…Previous studies have been useful in illuminating the role of cannabis in false memory production but have several drawbacks: Specifically, in Riba et al (2015), the participants were abstinent for at least 4 weeks, making it difficult to determine acute intoxication effects, whereas in Ballard et al (2012), the participants received a specific dose that may not account for individual differences in tolerance levels. While the Vredeveldt et al (2018) study advanced on this design by testing participants who chose their own cannabis dose, false memory was not measured directly using a method known to successfully lead to reliable levels of false memories. These drawbacks have been addressed in the current design.…”

“…Individuals who use cannabis may be involved in legal cases as witnesses or suspects where they have to provide accurate accounts of events. To date, two studies examining the acute effects of cannabis on eyewitness memory (e.g., memory for a crime film or staged crime) have been conducted (Vredeveldt et al 2018; Yuille et al 1998). These studies did not find that cannabis intoxication led to a higher rate of incorrect recall.…”

Cannabis increases susceptibility to false memory

“…Another element of the current experiment was that we used virtual reality (VR) as a way to test the misinformation effect in subjects acting as eyewitnesses and perpetrators. Studies have traditionally employed methods such as case vignettes or videos (22), but also staged events (23), to expose participants to a mock crime event, presenting a trade-off of either maximizing internal or external validity. The scenarios in this study were administered in VR, a fully immersive technology that can overcome this trade-off by combining high experimental control and reusability with high degrees of realism, ecological validity, and feelings of presence (24).…”

Hazy memories

“…In sum, there is evidence that acute cannabis but also residual use can increase false memory proneness and suggestibility, which seems to be driven largely by THC at retrieval elevating response bias but also increasing the potential for false memories when an event was experienced while intoxicated. For general studies on cannabis and eyewitness memory see Vredeveldt et al (2018), Pezdek et al (2020) and Yuille et al (1998).…”

“…Only a handful of studies however exist with research methodologies specifically aimed at inducing and testing false memories and suggestibility (see Chapter 2). Recently, researchers have turned to studying cannabis in an eyewitness memory context (Pezdek et al, 2020;Vredeveldt et al, 2018; with one early exception by Yuille et al, 1998), but studies on false memory are scarce.…”