The effects of repetition spacing on the illusory truth effect

The illusory truth effect refers to the fact that repetition increases perceptions of truth. In these experiments, we examined whether the magnitude of the illusory truth effect varies based upon repetition spacing. In Experiment 1, participants read facts that repeated twice, with a lag of 0, 1, 2, 4, 8, 16, or 32 intervening facts. Participants later rated the truthfulness of these facts in addition to new facts. Here, we observed a spacing effect: Truth ratings were higher when repetitions were spaced (i.e., lags of 1 through 32) rather than massed (i.e., lag of 0). We also observed a lag effect that followed a quadratic pattern: Truth ratings increased up to a lag of 16, after which they decreased. In Experiment 2 we tested whether the spacing effect in truth ratings depends upon the number of repetitions. In Experiment 2a we used a small number of repetitions (2, 3, or 4) and short lag lengths (0, 1, or 2). In Experiment 2b, we increased the number of repetitions (2 or 10) and the lag lengths (0 or 10). In Experiment 2a there was an illusory truth effect, but its magnitude did not depend upon lag length or repetition number. However, in Experiment 2b the magnitude of the illusory truth effect increased as lag length and repetition number increased, but there was no interaction between these two factors. Together, these findings show that repetition is most likely to increase perceived truth when repetitions are spaced with a moderate number of intervening items.