Truthiness and law: Non-probative information biases perceived credibility in forensic contexts

Non-probative but related photos have been shown to increase the perceived truth value of statements relative to when no photo is presented. In 2 experiments, I tested whether this truth bias generalizes to judgements of credibility in a forensic context. Participants read short vignettes in which a witness viewed an offence. The vignettes were presented with or without a non-probative, but related photo. In both experiments, participants gave higher witness credibility ratings on average in photo-present vignettes compared to photo-absent vignettes. In Experiment 2, some vignettes included additional non-probative information in the form of text. I replicated the effect of photo presence in Experiment 2, but the non-probative text did not have a significant effect on witness credibility. The results suggest that non-probative photos can increase the perceived credibility of witnesses in legal contexts.