Monetary incentives do not reduce the repetition-induced truth effect

People rate and judge repeated information more true than novel information. This truth-by-repetition effect is of relevance for explaining belief in fake news, conspiracy theories, or misinformation effects. To ascertain whether increased motivation could reduce this effect, we tested the influence of monetary incentives on participants’ truth judgments. We used a standard truth paradigm, consisting of a presentation and judgment phase with factually true and false information, and incentivized every truth judgment. Monetary incentives may influence truth judgments in two ways. First, participants may rely more on relevant knowledge, leading to better discrimination between true and false statements. Second, participants may rely less on repetition, leading to a lower bias to respond “true.” We tested these predictions in a preregistered and high-powered experiment. However, incentives did not influence the percentage of “true” judgments or correct responses in general, despite participants’ longer response times in the incentivized conditions and evidence for knowledge about the statements. Our findings show that even monetary consequences do not protect against the truth-by-repetition effect, further substantiating its robustness and relevance and highlighting its potential hazardous effects when used in purposeful misinformation.

A reproducible systematic map of research on the illusory truth effect

People believe information more if they have encountered it before, a finding known as the illusory truth effect. But what is the evidence for the generality and pervasiveness of the illusory truth effect? Our preregistered systematic map describes the existing knowledge base and objectively assesses the quality, completeness and interpretability of the evidence provided by empirical studies in the literature. A systematic search of 16 bibliographic and grey literature databases identified 93 reports with a total of 181 eligible studies. All studies were conducted at Western universities, and most used convenience samples. Most studies used verbatim repetition of trivia statements in a single testing session with a minimal delay between exposure and test. The exposure tasks, filler tasks and truth measures varied substantially across studies, with no standardisation of materials or procedures. Many reports lacked transparency, both in terms of open science practices and reporting of descriptive statistics and exclusions. Systematic mapping resulted in a searchable database of illusory truth effect studies (https://osf.io/37xma/). Key limitations of the current literature include the need for greater diversity of materials as stimuli (e.g., political or health contents), more participants from non-Western countries, studies examining effects of multiple repetitions and longer intersession intervals, and closer examination of the dependency of effects on the choice of exposure task and truth measure. These gaps could be investigated using carefully designed multi-lab studies. With a lack of external replications, preregistrations, data and code, verifying replicability and robustness is only possible for a small number of studies.

Judgments of truth are independently modulated by affect and repetition

People believe repeated statements more than new ones—the repetition-induced truth effect. It is prominently explained with processing fluency: The subjective ease of processing repeated versus new information. To date, the role of affective processes for the truth effect is rather unclear. From a theoretical perspective, people should rely more on fluency under positive than under negative affect. Here, we tested whether an affective picture presented before a statement influences the repetition-induced truth effect. Thirty-five participants took part in two sessions that were a week apart. In both sessions, they rated the truth status of statements. In session 2, repeated and new statements were intermixed, and each statement was preceded by a positive, negative, or neutral picture. We expected participants to rely more on fluency as a cue to truth in the positive than in the negative affective condition. However, although we replicated the repetition-induced truth effect, the interaction between affect and repetition was insignificant, but we observed a significant main effect of affect—statements were rated as truer after a positive rather than a negative or neutral picture. Our results suggest two independent mechanisms that enhance the subjective truth of statements: repetition and positive affect.

Illusory Truth Occurs Even with Incentives for Accuracy

Fake news sites, politicians, and advertisers often make false claims believable by repeating them. Repeated statements feel easier to process, and thus truer, than new ones. In two large experiments (N = 1188), we investigated whether monetary incentives for accuracy reduce this 'illusory truth effect.' Repetition misled people regardless of whether they could earn money for correct answers. The illusion occurred even when participants received item-by-item reminders about possible rewards. Our findings suggest that motivation is not always enough to disengage people from using heuristics to evaluate truth, with implications for a “post-truth world.”

Truth by Repetition … without repetition: Testing the effect of instructed repetition on truth judgments

Past research indicates that people judge repeated statements as more true than new ones. An experiential consequence of repetition that may underly this “truth effect” is processing fluency: processing statements feels easier following their repetition. Here, we examine the effect of merely instructed (i.e., not experienced) repetition on truth judgments, which we compared to the effect of factual repetition. In two preregistered experiments (N=468), we found a larger truth effect for factual repetition compared to instructed repetition. However, we also found a non-experiential contribution to truth judgments: statements instructed to be repeated were judged more true than those instructed to be new. Experiment 2 further clarified that adding a repetition status tag in the factual repetition condition did not impact truth judgments. Moreover, for both experienced and instructed repetition, the effect on truth was qualified by subjective recognition. We discuss the mechanisms that can explain the impact of instructed repetition on truth and its implications for a better understanding of the truth effect.

Backfire effects after correcting misinformation are strongly associated with reliability

The backfire effect is when a correction increases belief in the very misconception it is attempting to correct, and it is often used as a reason not to correct misinformation. The current study aimed to test whether correcting misinformation increases belief more than a no-correction control. Furthermore, we aimed to examine whether item-level differences in backfire rates were associated with test-retest reliability or theoretically meaningful factors. These factors included worldview-related attributes, namely perceived importance and strength of pre-correction belief, and familiarity-related attributes, namely perceived novelty and the illusory truth effect. In two nearly identical experiments, we conducted a longitudinal pre/post design with N = 388 and 532 participants. Participants rated 21 misinformation items and were assigned to a correction condition or test-retest control. We found that no items backfired more in the correction condition compared to test-retest control or initial belief ratings. Item backfire rates were strongly negatively correlated with item reliability (⍴ = -.61 / -.73) and did not correlate with worldview-related attributes. Familiarity-related attributes were significantly correlated with backfire rate, though they did not consistently account for unique variance beyond reliability. While there have been previous papers highlighting the non-replicable nature of backfire effects, the current findings provide a potential mechanism for this poor replicability. It is crucial for future research into backfire effects to use reliable measures, report the reliability of their measures, and take reliability into account in analyses. Furthermore, fact-checkers and communicators should not avoid giving corrective information due to backfire concerns.

The effects of repetition frequency on the illusory truth effect

Repeated information is often perceived as more truthful than new information. This finding is known as the illusory truth effect, and it is typically thought to occur because repetition increases processing fluency. Because fluency and truth are frequently correlated in the real world, people learn to use processing fluency as a marker for truthfulness. Although the illusory truth effect is a robust phenomenon, almost all studies examining it have used three or fewer repetitions. To address this limitation, we conducted two experiments using a larger number of repetitions. In Experiment 1, we showed participants trivia statements up to 9 times and in Experiment 2 statements were shown up to 27 times. Later, participants rated the truthfulness of the previously seen statements and of new statements. In both experiments, we found that perceived truthfulness increased as the number of repetitions increased. However, these truth rating increases were logarithmic in shape. The largest increase in perceived truth came from encountering a statement for the second time, and beyond this were incrementally smaller increases in perceived truth for each additional repetition. These findings add to our theoretical understanding of the illusory truth effect and have applications for advertising, politics, and the propagation of “fake news.”

How Repetition Affects What Kids and Adults Believe

How do you know that something is true? Is it because you learned it in school? Is it because you heard it before? Our brains can remember a lot of information, but we do not always use this information when deciding what is true. Sometimes we use shortcuts like, “Have I heard this before?” rather than thinking about what we know. These shortcuts can lead us to make mistakes—like thinking that a false statement is true just because you have heard it many times. Researchers call this the illusory truth effect. People are more likely to believe information they have heard multiple times. This happens even when people should know that what they are hearing is wrong! They already have the correct information stored in memory, but repetition makes them think that false information is true. In this article, we discuss why this happens, and how this might affect kids like you!

Is it all about the feeling? Affective and (meta-)cognitive mechanisms underlying the truth effect

People are more likely to judge repeatedly perceived statements as true. A decisive explanation for this so-called truth effect is that the repeated information can be processed more fluently than new information and that this fluency experience renders the information more familiar and trustworthy. Little is known, however, regarding whether and how affective states and dispositional cognitive preferences influence the truth effect. To this end, we conducted two experiments in which we manipulated (a) processing fluency via repetition, (b) the time interval (10 min vs. 1 week) between repetitions, and (c) short-term affective states using the presentation of emotional faces (Experiment 1) or the presence of an irrelevant source for changes in affective states (Experiment 2). Additionally, we assessed the dispositional variables need for cognitive closure (NCC), preference for deliberation (PD) and preference for intuition (PI). Results of Experiment 1 showed that the truth effect was significantly reduced for statements that were followed by a negative prime, although this was the case only for the longer repetition lag. Furthermore, higher NCC and lower PD scores were associated with an increased truth effect. Results of Experiment 2 replicated the moderating role of NCC and further showed that participants, who were provided with an alternative source for changes in their affective states, showed a reduced truth effect. Together, the findings suggest that (a) fluency-related changes in affective states may be (co-)responsible for the truth effect, (b) the truth effect is decreased when the repetition interval is long rather than short, and (c) the truth effect is increased for individuals with a higher need for cognitive closure. Theoretical implications of these findings are discussed.

Judging fast and slow: The truth effect does not increase under time-pressure conditions

Dual-process theories propose that information can be processed in two different ways: fast and intuitively or slow and deliberatively. Based on this idea, we tested whether time pressure increases the repetition-based truth effect—the tendency to judge repeatedly encountered statements more likely as “true” than novel statements. We expected that time pressure would boost the truth effect by increasing reliance on processing fluency as a presumably intuitive cue for truth, and by decreasing knowledge retrieval as a presumably slow and analytic process that determines truth judgments. Contrary to these predictions, however, a series of three experiments did not provide any empirical evidence that the truth effect is moderated by time pressure. We interpret our results in terms of the referential theory of the truth effect which assumes that truth judgments depend on the coherence of localized networks in people’s semantic memory that a statement activates. Building on this account we conclude that truth judgments largely depend on automatic processes, at least when people evaluate isolated statements.