Expert opinions on the smallest effect size of interest in false memory research

External and internal influences yield similar memory effects: the role of deception and suggestion

In legal cases, testimonies can become contaminated because of an amalgam of external and internal influences on memory. It is well-established that external influences (e.g., suggestive interviews) can hurt memory. However, less focus has been placed on the impact of internal influences (e.g., lying) on memory. In the current review, we show that the available evidence suggests that both external and internal influences exert similar effects on memory. That is, we review studies showing that suggesting non-occurrences and suggesting non-experiences can lead to omission errors and false memories, respectively. Likewise, these memory effects are also observed when focusing on internal influences. That is, false denials, feigning amnesia and fabrication have been shown to affect memory in terms of forgetting (i.e., omissions) and false memories (i.e., commissions). Also, we show that both external and internal influences can lead to changes in the belief that an event occurred. We argue that in legal cases, triers of fact should concentrate on whether both types of influences might have affected testimonial accuracy in witnesses, victims, and suspects.

No gesture too small: An investigation into the ability of gestural information to mislead eyewitness accounts by 5- to 8-year-olds

The accuracy of eyewitness interviews has legal and clinical implications within the criminal justice system. Leading verbal suggestions have been shown to give rise to false memories and inaccurate testimonies in children, but only a small body of research exists regarding non-verbal communication. The present study examined whether 5- to 8-year-olds in the UK could be misled about their memory of an event through exposure to leading gestural information, which suggested an incorrect response, using a variety of question and gesture types. Results showed that leading gestures significantly corrupted participants' memory compared to the control group (MD = 0.60, p < 0.001), with participants being misled by at least one question nearly three-quarters of the time. Questions about peripheral details, and gestures that were more visible and expressive, increased false memory further, with even subtle gestures demonstrating a strong misleading influence. We discuss the implications of these findings for the guidelines governing eyewitness interviews.

The importance of the smallest effect size of interest in expert witness testimony on alcohol and memory

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.