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

truth of climate-science and climate-skeptic aligned claims for all recipients, theorizing about motivated cognition suggests that recipients’ pre-exposure attitudes should limit the impact of counter-attitudinal claims. We address both lines of theorizing in turn. Metacognitive theorizing: The illusory truth effect Metacognitive research shows that people attend to the content of a claim and the subjective experiences that accompany its processing when they evaluate its merits [6]. When information feels easy to process—a claim is easy to perceive, easy to imagine, or easy to retrieve—people judge it as more likely to be true [7]. Feelings of ease or difficulty can arise from attributes that provide valid information about a claim as well as from purely incidental influences. For exam- ple, a coherent and logically valid argument is easier to comprehend than an incoherent one and may warrant a higher rating of truth [8]. But an experience of easy processing can also arise from tangential influences that are not diagnostic of truth, such as the simple repetition of a claim. Repeated claims are processed more quickly, a classic (and robust) finding in repetition priming [9]. Because people are more sensitive to their feelings than to the source that elicited them, they usually draw on their momentary feelings when forming a judgment [10]. Hence, they use ease of processing as an informative cue to truth, regardless of whether the argument was coherent [11], has been repeated [12], or was simply presented in an easier to read color

contrast [13–15]—whenever a claim is easy to process, it is more likely to “feel right” [6]. The power of mere repetition is captured in a classic paradigm from cognitive psychology named the illusory truth effect (ITE) [2, 12, 16]. In the ITE paradigm, people view a series of claims during an initial exposure phase. After a short delay, they rate the perceived truth of another series of claims, half of which they have seen during the exposure phase (repeated claims) and half of which are new (non-repeated). Which claims are repeated or new is coun- terbalanced across participants, allowing researchers to assess the impact of repetition on judged truth. Since its discovery in 1977 [12], the key finding is among the most robust results in cognitive psychology: a given claim is more likely to be judged true when it has been encountered before. Moreover, a single repetition is sufficient to produce this illusory truth effect [2]. Recent reviews have highlighted the robustness of the ITE across different contexts and domains of judgment. The tendency to believe repeated claims holds not only for unfamiliar claims, but also for claims that people can later identify as false on the basis of their general knowledge [17]. Informing people about the influence of repetition [18], warning them that some of the statements are false [19] or come from a low credibility source [20, 21], attenuates the ITE but does not eliminate it. ITE effects have been observed in many domains, including trivia statements [22], opinions of others [23], product-related claims [24, 25], strong and

weak arguments [26], and fake news headlines [27]. However, little is known about the extent to which repetition affects people’s assessments of truth when claims are clearly counter-attitu- dinal and at odds with strongly held prior beliefs. Motivated cognition In contrast, strongly held prior beliefs have received extensive attention in motivated cognition research. In this domain, researchers assume that people are likely to reject claims that run counter to their own beliefs and exhibit a disconfirmation bias [28–31]. Arguments that are inconsistent with recipients’ beliefs or political ideology are processed more slowly, as indi- cated by longer reading times, and elicit more counter-arguing [32–34], which limits their acceptance [35, for a review]. People also perceive counter-attitudinal claims as less accurate than pro-attitudinal claims that are aligned with their own position on a given topic [36, 37]. PLOS ONE Illusory truth effect for climate-skeptical claims PLOS ONE | https://doi.org/10.1371/journal.pone.0307294 August 7, 2024 2 / 19