The Influence of Expertise and Language Proficiency on Lie Truth Detection and Truth Bias in the Legal System

ABSTRACT The present study examined how professional expertise and language proficiency affect lie‐truth detection accuracy and truth bias in a legal context by comparing experts (court judges, prosecutors, lawyers; n = 97) with laypersons ( n = 95). To this end, a preregistered mixed‐design online study was conducted in which participants judged the credibility of 16 video messages delivered by native and non‐native German speakers in an interrogation situation. Contrary to expectations, no group difference was found in overall detection accuracy or response bias. Furthermore, non‐native speakers were not perceived as less credible overall. However, experts were more likely to judge messages from native speakers as truthful, whereas laypersons were more inclined to judge messages from non‐native speakers as truthful. These findings highlight the potential for response bias in experts' veracity judgments of non‐native speakers and underscore the need for further research aimed at reducing discrimination in legal decision‐making.