Repetition increases belief in climate-skeptical claims, even for climate science endorsers

consequences of repeating false information. It is therefore important to emphasize and repeat what is true and not to repeat what is false. These findings are consistent with a growing body of research showing that people draw on both declarative information (the content of the claims) and experiential information (how easy it is to process the claims) in forming judgments of truth [6, 7, 13–15, 47, 48]. In the pres- ent studies, our climate science endorsing participants perceived claims aligned with climate scientists as more truthful than claims aligned with climate skepticism, a difference that reflects the content of the claims. However, both types of claims seemed truer when they were repeated than when they were not, reflecting the influence of repetition-based fluency. The influence of repetition held even for claims that participants self-classified as counter-attitudinal when we asked them to categorize each claim as climate scientist-aligning or climate skeptic-aligning (Experiment 2). When we used participants’ own classifications—thus ensuring that they knew a claim was skeptic-aligning—our climate science endorsing participants still considered repeated skeptic-aligning claims more truthful. This confirms that the influence of repetition on the acceptance of counter-attitudinal claims was not driven by misconceptions of the con- tent of claims; instead, repeated exposure has a profound effect on people’s judgments even when they can personally identify a given claim as being at odds with their own position. Com-

patible with this conclusion, related work suggests that repeated exposure to fake news head- lines featuring polarizing political figures increases acceptance of the fake news, even when the fake headline themes are likely at odds with the perceivers’ own political orientation [27]. Such pervasive effects are compatible with the observation that people have little insight into the influence of metacognitive experiences, in particular when those experiences are elicited by subtle incidental manipulations like repetition [12], color contrast [13], print fonts [49], or acoustic quality [7, 50]. This lack of insight limits people’s ability to protect against their impact, as indicated by the observation that individual differences in critical reasoning do not moderate the influence of claim repetition [51, 52]. Our findings have mixed implications for theories of motivated reasoning that assume that people with pre-existing beliefs treat pro-attitudinal information with a confirmation bias and counter-attitudinal information with a disconfirmation bias [29, 53–56]. Compatible with such theories, our participants perceived claims that were aligned with climate scientists as truer than claims aligned with climate skeptics. But challenging such theories, the motivated acceptance and rejection of claims was still susceptible to the effects of repetition. This observa- tion is especially noteworthy because our experimental procedures rendered participants’ own pre-experimental attitudes highly salient—we asked them to rate their own attitudes towards

climate science right before seeing any of the claims. As Cotter and colleagues [57] noted in their discussion of boundary conditions of moti- vated reasoning, motivated biases are strongest under conditions of identity threat [58] and people are more receptive to counter-attitudinal information when self-affirmation procedures attenuate threats to the self [59, 60]. From this perspective, the exposure to a mix of counter- attitudinal and pro-attitudinal claims may not have been sufficiently threatening to elicit a strong disconfirmation bias. Future research may fruitfully explore whether a more confronta- tional presentation of counter-attitudinal claims renders repetition less influential. Blocking counter-attitudinal claims—rather than interspersing them with pro-attitudinal claims—may increase their threat effect, as may more extreme wordings or manipulations that highlight the identity relevance of one’s pre-existing attitudes. Further extensions of this research might also consider the combined effect of counter-attitudinal claims shared by low credibility sources as another possible condition that increases identity threat. While the illusory truth effect litera- ture generally shows that repetition continues to increase perceptions of truth regardless of PLOS ONE Illusory truth effect for climate-skeptical claims PLOS ONE | https://doi.org/10.1371/journal.pone.0307294 August 7, 2024 14 / 19