The Effect of Repetition on Truth Judgments Across Development

According to numerous research studies, when adults hear a statement twice, they are more likely to think it is true compared with when they have heard it only once. Multiple theoretical explanations exist for this illusory-truth effect. However, none of the current theories fully explains how or why people begin to use repetition as a cue for truth. In this preregistered study, we investigated those developmental origins in twenty-four 5-year-olds, twenty-four 10-year-olds, and 32 adults. If the link between repetition and truth is learned implicitly, then even 5-year-olds should show the effect. Alternatively, realizing this connection may require metacognition and intentional reflection, skills acquired later in development. Repetition increased truth judgments for all three age groups, and prior knowledge did not protect participants from the effects of repetition. These results suggest that the illusory-truth effect is a universal effect learned at a young age.