Voice parade procedures: optimising witness performance

A meta-analysis on study and sample characteristics modulating mock earwitness performance

Mock earwitness performance mainly addresses cognitive functions like free recall and recognition of auditory information. Based on primary studies a-priori experimental moderator effects on mock earwitness performance have been hypothesized. Including 46 articles with k = 66 experimental studies, a bare-bones and a random-effects, artefact-corrected meta-analysis have been performed. The results show a substantial ratio of the population effect size and the standard deviation of the population effect size (δ/SDδ) for the a-priori moderators bimodal compared to unimodal stimuli and for gender of listener. These results indicate that bimodal stimuli compared to unimodal stimuli yield substantially better mock earwitness performance. Women outperform men in mock earwitness performance. The fail-safe number demonstrates robust population effects for both a-priori moderators. As a post-hoc moderator, line-ups with target-present revealed substantial δ/SDδ ratios for stimulus length and gender of listener. These results for post-hoc moderators suggest that longer compared to shorter stimuli reveal better mock earwitness performance. The gender of listener effect is in target-present line-ups comparabale to the before mentioned gender of listener effect. G*Power calculations for future primary studies suggest that sample sizes in several primary studies were too small. Single-person earwitness assessments should be substantiated by reality monitoring and disentangled from hearsay evidence (i.e., situations in that individuals have heard information from other persons). The data recommend that best-practice options for earwitnesses in court settings should be derived from meta-analytic results, corresponding to the jurisdictions of the countries and exclusively for results that were substantial (δ/SDδ ratios) and robust (fail-safe number).

Identifying unfamiliar voices: Examining the system variables of sample duration and parade size

Voice identification parades can be unreliable due to the error-prone nature of earwitness responses. UK government guidelines recommend that voice parades should have nine voices, each played for 60 s. This makes parades resource-consuming to construct. In this article, we conducted two experiments to see if voice parade procedures could be simplified. In Experiment 1 (N = 271, 135 female), we investigated if reducing the duration of the voice samples on a nine-voice parade would negatively affect identification performance using both conventional logistic and signal detection approaches. In Experiment 2 (N = 270, 136 female), we first explored if the same sample duration conditions used in Experiment 1 would lead to different outcomes if we reduced the parade size to include only six voices. Following this, we pooled the data from both experiments to investigate the influence of target-position effects. The results show that 15-s sample durations result in statistically equivalent voice identification performance to the longer 60-s sample durations, but that the 30-s sample duration suffers in terms of overall signal sensitivity. This pattern of results was replicated using both a nine- and a six-voice parade. Performance on target-absent parades were at chance levels in both parade sizes, and response criteria were mostly liberal. In addition, unwanted position effects were present. The results provide initial evidence that the sample duration used in a voice parade may be reduced, but we argue that the guidelines recommending a parade with nine voices should be maintained to provide additional protection for a potentially innocent suspect given the low target-absent accuracy.

Assessing the Specificity and Accuracy of Accent Judgments by Lay Listeners

Historically, there has been less research carried out on earwitness than eyewitness testimony. However, in some cases, earwitness evidence might play an important role in securing a conviction. This paper focuses on accent which is a central characteristic of voices in a forensic linguistic context. The paper focuses on two experiments (Experiment 1, n = 41; Experiment 2, n = 57) carried out with participants from a wide range of various locations around the United Kingdom to rate the accuracy and confidence in recognizing accents from voices from England, Scotland, Wales, Northern Ireland, and Ireland as well as looking at specificity of answers given and how this varies for these regions. Our findings show that accuracy is variable and that participants are more likely to be accurate when using vaguer descriptions (such as "Scottish") than being more specific. Furthermore, although participants lack the meta-linguistic ability to describe the features of accents, they are able to name particular words and pronunciations which helped them make their decision.

Evaluating earwitness identification procedures: adapting pre-parade instructions and parade procedure

Voice identification parades can be unreliable, as earwitness responses are error-prone. In this paper we tested performance across serial and sequential procedures, and varied pre-parade instructions, with the aim of reducing errors. The participants heard a target voice and later attempted to identify it from a parade. In Experiment 1 they were either warned that the target may or may not be present (standard warning) or encouraged to consider responding "not present" because of the associated risk of a wrongful conviction (strong warning). Strong warnings prompted a conservative criterion shift, with participants less likely to make a positive identification regardless of whether the target was present. In contrast to previous findings, we found no statistically reliable difference in accuracy between serial and sequential parades. Experiment 2 ruled out a potential confound in Experiment 1. Taken together, our results suggest that adapting pre-parade instructions provides a simple way of reducing the risk of false identifications.