Cognitive processes underlying the repetition-based truth effect: A diffusion model study

People are more likely to judge repeated (vs. novel) information as true. This illusory truth effect is commonly attributed to increased processing fluency, with perceptual and semantic aspects of repetition assumed to enhance perceptual and conceptual fluency, respectively. While prior research has shown that the truth effect is affected by the temporal gap between presentations, the cognitive mechanisms underlying this effect-and how they are shaped by retention interval-remain insufficiently understood. In Experiment 1 (N = 75), we manipulated repetition (repeated vs. new statements) and retention interval (10 min vs. 1 week) within participants. Using diffusion modeling, we found that repetition increased drift rate, reduced nondecision time, and induced a bias toward "true" responses-suggesting contributions from both conceptual and perceptual fluency. These effects diminished with increasing retention interval. In Experiment 2 (N = 81), participants judged the validity of one-word answers to previously shown questions, allowing separate measurement of reading times and tighter control over nondecision time. When modeling only the answer-related response times, repetition did not affect drift rate, but the repetition-enhanced response bias remained. Reading times for repeated questions were reduced, indicating facilitated encoding. An additional analysis using total trial reaction times (reading + response time) revealed a repetition effect on drift rate, suggesting that information accumulation may begin during question reading. Together, these findings indicate that the illusory truth effect results from a combination of perceptual facilitation, response bias, and increased speed of information accumulation supporting the truthfulness of a statement-each contributing at different stages of the decision process. (PsycInfo Database Record (c) 2026 APA, all rights reserved).