The Effect of Repetition on Truth Judgments Across Development

Abstract

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.

Keywords

truth repetition illusory truth children misinformation open data open materials preregistered

When deciding whether statements are true or false in laboratory settings, adults who hear a statement twice are more likely to think that it is true compared with when they have heard it only once. This illusory-truth effect has been found in over 100 studies over the past 40 years (see Dechêne, Stahl, Hansen, & Wänke, 2010, for a meta-analytic review). The effect occurs with trivia facts (Hasher, Goldstein, & Toppino, 1977), political opinions (Arkes, Hackett, & Boehm, 1989), and even false news headlines (Pennycook, Cannon, & Rand, 2018). It also occurs with statements that contradict people’s existing knowledge—for example, “The skirt that Scottish men wear is called a sari” (Fazio, 2020; Fazio, Brashier, Payne, & Marsh, 2015). These findings have taken on new importance in the modern world, where misinformation and false statements are repeatedly presented by politicians and on social media.

Multiple theories exist about why repetition increases perceived truth (see Unkelbach, Koch, Silva, & Garcia-Marques, 2019, for a review). One explanation is that repetition increases the familiarity of a statement, and people believe that things they have heard before are likely true (Arkes et al., 1989). A second is that repeated statements are more easily processed and understood than novel statements and that this ease of processing, or fluency, is used as a signal for truth in a similar way that it is used as a signal for memory and other judgments (e.g., Alter & Oppenheimer, 2006; Jacoby, Kelley, Brown, & Jasechko, 1989; Jacoby, Kelley, & Dywan, 1989; Tversky & Kahneman, 1973; Unkelbach, 2007; Unkelbach & Greifeneder, 2013). Thus, other manipulations that increase ease of processing, such as high-contrast font colors or predictable rhymes, also increase truth ratings (McGlone & Tofighbakhsh, 2000; Reber & Schwarz, 1999; Silva, Garcia-Marques, & Mello, 2016). Finally, recent research suggests that repetition may increase the cohesiveness of the concepts represented in the statement in memory and that this cohesiveness is used as a signal for truth (Unkelbach & Rom, 2017). Manipulations that increase the cohesiveness of the network, such as deeper processing, increase the illusory-truth effect (Unkelbach & Rom, 2017). All three theories are related and somewhat overlapping; increasing the cohesiveness of the representation through deeper processing also likely increases ease of processing, and repetition increases familiarity, fluency, and cohesiveness. It is likely that all of these processes play a role in the illusory-truth effect.

For all three theories, however, a key unexplained step is how people first begin to associate familiarity, fluency, or a coherent referential network with truth. Examining the development of the repetition-induced truth effect can help answer this question. One possibility is that our brains naturally and automatically track the relevant statistics and quickly realize the correlation between these proximal cues and truth. That is, through implicit or statistical learning, people realize that statements that are familiar, cohesive, and fluent are also likely to be true (e.g., Aslin, 2017; Frost, Armstrong, Siegelman, & Christiansen, 2015; Thiessen, Kronstein, & Hufnagle, 2013). Note that this is similar to the learning-from-feedback account provided by Unkelbach and Greifeneder (2013). If this is the case, children should begin to show the effect as soon as they understand the concept of truth. Alternatively, the effect may occur only for older children who have more experience intentionally reflecting on their experiences and what is true or false. That is, through metacognition, people may develop a naive theory that these proximal cues are a signal for truth (e.g., Schwarz, 2010).

Children’s Metacognitive Abilities and Their Understanding of Truth

Children begin to notice inaccurate statements at a young age. Sixteen-month-olds look longer at speakers who mislabel familiar objects (Koenig & Echols, 2003), and preschoolers can accurately indicate whether a speaker is labeling objects correctly or incorrectly (Koenig, Clément, & Harris, 2004). By the age of 5, children use their knowledge of the world to judge the reality status of novel creatures. Novel animals with typical features (e.g., “A Jarpat is kind of like a lion. It roars.”) are judged as real, and novel animals with atypical or impossible features (e.g., “A Calak is kind of like a horse. It climbs trees.”) are judged as not real (Lopez-Mobilia & Woolley, 2016). Similarly, 5- and 6-year-old children reject the idea that novel animals can accomplish counterintuitive actions (e.g., “Spalts can jump very high. They can jump so high that they can jump over hills.”; Lane & Harris, 2015).

However, 5-year-olds are still developing their metacognitive skills (see Schneider, 2008, for a review). In particular, they are still learning the relation between different internal cues and later memory or belief. For example, 7- and 8-year-olds do not yet realize that there is an inverse relation between study time and later recall (items that require more effort to encode are less likely to be recalled on a later test; Koriat, Ackerman, Lockl, & Schneider, 2009a, 2009b). These metacognitive abilities continue to improve during adolescence; older teens are better able to monitor the accuracy of their task performance than younger teens (Weil et al., 2013).

Statement of Relevance

In a world where misinformation is prevalent and spreads rapidly throughout society, it is essential to be able to distinguish truth from falsehood. Yet prior research demonstrates that people often use unreliable cues, such as repetition, to judge truth rather than more accurate cues, such as their prior knowledge or the source of the information. In this study, we examined the developmental origins of this illusory-truth effect. Among 5-year-olds, 10-year-olds, and adults, we found that repeated statements were more likely to be judged as true compared with statements presented only one time. In addition, prior knowledge did not protect against this effect. Even adults were more likely to say that the false statement “a calf is a baby horse” was true when it was repeated. These findings suggest that the illusory-truth effect occurs across development and for a variety of statements. We should all be wary of the dangers of repeating false information.

There is some preliminary evidence that young children may use processing fluency as a signal for truth. When guessing where a ball was hidden, 4- and 5-year-olds were more likely to rely on the testimony of a character who spoke fluently compared with a disfluent character whose speech was overlaid with digital noise (Bernard, Proust, & Clément, 2014). However, there were a number of differences between this paradigm and the typical illusory-truth effect. The most important is that the spoken messages were in direct conflict, so the child was forced to side with only one of the characters. When forced to choose between a fluent and disfluent speaker, young children relied on the fluent testimony, but if the speakers were presented sequentially, the children may have believed both speakers. Thus, it is unclear how young children will react in the illusory-truth paradigm, in which each statement is presented individually and children are asked whether it is true or false.

Effects of Prior Knowledge

A secondary goal of this research was to replicate previous research on the effects of prior knowledge on the illusory-truth effect. Studies have shown that repetition increases perceived truth, even when people have prior knowledge that contradicts the repeated falsehood (Fazio, 2020; Fazio et al., 2015), and that repetition affects belief similarly for both plausible and implausible statements (Fazio, Rand, & Pennycook, 2019). To confirm and extend these findings, we designed our stimuli so that each age group would have relevant prior knowledge for some statements and limited knowledge about others.

This manipulation also allowed us to examine how knowledge and repetition interact to produce truth judgments. Our previous research suggests that people do not always consult their prior knowledge when making truth judgments and instead rely only on fluency or other proximal signals (Fazio et al., 2015). That work contrasted two different processing-tree models. In each model, the parameters represent the probability that a specific unobserved cognitive process contributes to the observed behavior. In the knowledge-conditional model (Fig. 1, top), people primarily use their prior knowledge to make truth judgments; only when that knowledge search fails do people rely on fluency. In contrast, in the fluency-conditional model (Fig. 1, bottom), people are able to rely on fluency alone to make their judgments (without consulting prior knowledge). Note that although we use the term fluency in the models, participants may be relying on any cue that increases with repetition (fluency, familiarity, or cohesion). With adults, the fluency-conditional model provided a good fit for participants’ responses, but the knowledge-conditional model did not (Fazio et al., 2015). In the current study, we used the same two models to examine the response patterns of both children and adults.

Fig. 1.

Knowledge-conditional and fluency-conditional models of illusory truth. Parameter values represent the probability that the cognitive process contributes to the behavior. K = knowledge; F = fluency; G = guess “true.”

The Current Study

The current study examined the effect of repetition on the truth ratings of 5-year-olds, 10-year-olds, and college students. Our main question was whether 5- and 10-year-old children use repetition as a cue for truth. As a secondary interest, we also examined whether prior knowledge protects against the illusory-truth effect. The experiment consisted of two phases. During an exposure phase, participants rated true and false statements as “interesting” or “not interesting.” Then, during the truth phase, participants were asked to judge whether statements were “true” or “not true.” Some of these statements were new, and some were repeated from the exposure phase. To examine the interaction between the effects of prior knowledge and repetition, we varied the difficulty of the statements. For some, even the 5-year-olds should have prior knowledge to confirm or disprove the statements. For others, the truth status was likely unknown even to the adults. If the connection between repetition and truth is learned relatively quickly and implicitly, then all age groups should be more likely to rate the repeated statements as true than the new statements. If, however, people slowly develop a naive theory of truth through reflection and metacognition, then repetition may not have an effect until later in development.

Method

Participants

The participants were twenty-four 5-year-old children (age: M = 5.39, SD = 0.27), twenty-four 10-year-old children (age: M = 10.57, SD = 0.29), and 32 adults. We preregistered our intention to recruit 25 participants for each age group, but we decided to stop at 24 in order to have even numbers in each condition. Our past research with a binary true/not-true decision yielded an illusory-truth effect size (d) of 0.58 (Fazio et al., 2015). A power analysis using G*Power suggested that for a one-sided t test (predicting more “true” judgments for repeated statements), 20 participants per group would be required to detect an effect of that size with 80% power and an alpha of .05 (Faul, Erdfelder, Lang, & Buchner, 2007). We recruited a larger-than-expected number of adult participants because an overzealous research assistant posted extra time slots. The children were recruited using state birth records from Nashville, Tennessee, and from community events. Each child received a small toy worth less than $5 as compensation. The adult participants were recruited from Vanderbilt University’s participant pool and received course credit for their participation. An additional four 5-year-olds were excluded for missing at least two of the three practice questions (a preregistered exclusion criterion).

Design

The experiment was conducted in the laboratory during a single session and consisted of two phases: an exposure phase and a truth phase. The experiment had a 2 (repetition: new, repeated) × 2 (statement truth: truth, falsehood) × 3 (knowledge level: preschool, elementary school, middle school) × 3 (age: 5-year-olds, 10-year-olds, adults) mixed design. Repetition, statement truth, and knowledge level were all manipulated within subjects, and age was a between-subjects factor.

Materials

We selected 48 nature facts as stimuli. To ensure that some facts would be known by all of the participants and others would be unknown, we selected items from three versions of the game Brain Quest. One third of the statements came from the preschool and kindergarten games (Feder & Bishay, 2016b, 2016c), one third came from the game designed for third graders (Feder & Bishay, 2012), and the rest came from the game designed for seventh graders (Feder & Bishay, 2016a). Because of the limited number of nature-related facts in the seventh-grade game, we added eight nature facts from an online article (Stryker, 2014) and two from a set of general-knowledge norms (Tauber, Dunlosky, Rawson, Rhodes, & Sitzman, 2013). For each correct fact, we created a matching falsehood that referred to a plausible but incorrect alternative (e.g., “A spider has six legs”). Sample statements can be seen in Table 1, and the full set of materials is available online (https://osf.io/hw3gy).

Table 1.

Sample True and False Statements From Each Knowledge Level

True	False
Knowledge level: preschool
A calf is a baby cow.	A calf is a baby horse.
Tomatoes grow above ground.	Potatoes grow above ground.
A sheep is the animal that wool comes from.	A goat is the animal that wool comes from.
Knowledge level: elementary school
The dodo is an animal that is extinct.	The emu is an animal that is extinct.
Reptiles are cold-blooded animals.	Birds are cold-blooded animals.
Porcupines raise their quills to defend themselves.	Porcupines shoot their quills to defend themselves.
Knowledge level: middle school
Cumulonimbus clouds often bring thunderstorms.	Cirrus clouds often bring thunderstorms.
All clownfish are born male.	All clownfish are born female.
Antarctica is the largest desert on Earth.	The Sahara is the largest desert on Earth.

To counterbalance statement truth and repetition across participants, we divided the 16 statements in each knowledge level into four sets of four statements. For each participant, we presented one set as new truths, one set as new falsehoods, one set as repeated truths, and one set as repeated falsehoods. Which set appeared in each format was counterbalanced across participants.

Procedure

For the child participants, informed consent was obtained from the parent or guardian, and verbal or written assent was obtained from each participant. The entire experiment was presented on a touch-screen computer, and both the instructions and the statements were presented verbally. (The instructions were provided by the experimenter, and the statements were presented by the computer.)

The experiment began with the exposure phase. The children were introduced to a digital cartoon character named Ruby the Robot, who was going to tell them about animals and nature. They were told that “Ruby knows a lot about some things, and not a lot about other things. So, some of the things Ruby tells you will be true, and some will be not true.” The child’s job was to listen to each statement and decide whether it was “interesting” or “not interesting.” The children indicated their choice by pressing the relevant button on the touch screen (see Fig. 2). For the first few trials, the “interesting” and “not interesting” buttons were labeled by the experimenter to ensure that the younger children knew which was which. Twenty-four of the 48 statements were presented during the exposure phase. After the exposure phase, participants had a quick break, during which they worked on mazes or connect-the-dots activities for approximately 90 s.

Fig. 2.

Screenshot from the exposure phase. Participants listened to a statement that was spoken aloud by Ruby the Robot and then indicated whether the statement was “interesting” or “not interesting” on the touch screen. Screenshots from the truth phase are available online at https://osf.io/hw3gy.

After the filler task, participants were asked to listen to more statements from the same cartoon character. They were reminded that “Ruby knows a lot about some things and not a lot about other things, so some of what you hear will be true and some will be not true.” The children were also told, “Ruby will tell you some things that you have already heard today and some new things.” For each statement, the children first decided whether it was “true” or “not true” and then whether they were “very sure” or “not so sure.” To ensure that the children understood the task and the rating scale, we first presented three very simple non-nature-related practice statements from the preschool and kindergarten Brain Quest games (e.g., “A hat goes on your feet”). Following our preregistration, we excluded any participant who incorrectly identified the truth of two or more practice statements. After the practice items, participants were presented with all 48 statements.

The adult study was similar, but the instructions were presented visually on the screen rather than verbally by the experimenter. At the start of the experiment, adults were told that “This adult study was created from a child study which is why Ruby, our talking robot, is used.” They then were given the exact same instructions and completed the exact same procedures as the child participants, although they responded using a mouse instead of the touch screen. In addition, instead of solving mazes, the adults worked on visuospatial puzzles between the exposure and truth phases.

Results

All data and supplemental analyses are available online at OSF, along with our preregistration of the primary analyses and sample size (https://osf.io/hw3gy).

Do 5- and 10-year-old children use repetition as a cue for truth?

As shown in Figure 3, all three age groups were more likely to rate repeated statements as true than new statements. As detailed in our preregistration, the primary analysis was a 2 (repetition: new, repeated) × 2 (statement truth: truth, falsehood) × 2 (age: 5-year-olds, 10-year-olds, adults) analysis of variance (ANOVA) on the proportion of statements that were rated as true. As would be expected, true statements (M = .78, 95% confidence interval, or CI = [.75, .81]) were more often rated as true than were false statements (M = .52, 95% CI = [.49, .55]), F(1, 77) = 255.19, p < .001, η_p² = .77. We also replicated the typical illusory-truth effect; repeated statements (M = .69, 95% CI = [.66, .73]) were more likely to be rated as true than new statements (M = .61, 95% CI = [.58, .64]), F(1, 77) = 32.37, p < .001, η_p² = .30. In addition, there was no interaction between repetition and age, F(2, 77) = 0.28, p = .754, η_p² = .01; the size of the illusory-truth effect was similar across the three age groups. (Note, however, that the study was underpowered to detect differences in the size of the effect between age groups.) The age groups did differ in their ability to distinguish between the true and false facts, F(2, 77) = 30.96, p < .001, η_p² = .45. As shown in Table 2, 10-year-olds and adults were better able to distinguish between the true and false statements than 5-year-olds. In addition, there was a marginal interaction between repetition and statement truth, F(1, 77) = 2.98, p = .088, η_p² = .04. Probably because of ceiling effects for the easier items, the illusory-truth effect was slightly larger for false statements than true statements. No other main effects or interactions were significant, largest F = 0.90, p = .412.

Fig. 3.

Proportion of new and repeated statements rated as true by each age group. Each dot represents one participant. The filled diamond represents the group mean, and error bars represent standard errors.

Table 2.

Average Proportion of Statements Rated as True, Split by Age Group, Knowledge Level, Repetition, and Statement Truth

Knowledge level and statement truth	5-year-olds		10-year-olds		Adults
Knowledge level and statement truth	New	Repeated	New	Repeated	New	Repeated
Preschool
True	.75 (.27)	.82 (.19)	.93 (.12)	.98 (.07)	.91 (.15)	.95 (.12)
False	.53 (.29)	.59 (.31)	.22 (.20)	.35 (.26)	.23 (.22)	.38 (.33)
Elementary school
True	.65 (.23)	.71 (.28)	.83 (.19)	.89 (.16)	.85 (.18)	.95 (.14)
False	.57 (.21)	.68 (.23)	.43 (.21)	.55 (.31)	.46 (.21)	.46 (.25)
Middle school
True	.55 (.29)	.59 (.33)	.65 (.23)	.70 (.27)	.64 (.30)	.73 (.24)
False	.58 (.27)	.67 (.24)	.54 (.26)	.72 (.27)	.65 (.28)	.77 (.21)
M
True	.65 (.19)	.71 (.22)	.80 (.10)	.85 (.10)	.80 (.14)	.87 (.11)
False	.56 (.19)	.65 (.18)	.40 (.15)	.54 (.19)	.45 (.15)	.54 (.20)

Note: Standard deviations are given in parentheses.

Similar results were found when we recoded participants’ responses into a 4-point scale (1= very-sure false, 2 = not-so-sure false, 3 = not-so-sure true, 4 = very-sure true). The full ANOVA results are presented in the Supplemental Analyses file at https://osf.io/hw3gy, but our key findings included an overall illusory-truth effect, F(1, 77) = 36.06, p < .001, η_p² = .32: repeated statements (M = 3.06, 95% CI = [2.99, 3.14]) were given higher truth ratings than new statements (M = 2.85, 95% CI = [2.76, 2.92]), and there was no interaction between age and repetition, F(2, 77) = 0.89, p = .413, η_p² = .02.

Finally, we examined whether repetition significantly increased the proportion of statements rated as true for each of the three age groups. Following the analyses outlined in our preregistration, we found a significant illusory-truth effect for the 5-year-olds (new: M = .61, repeated: M = .68), t(23) = 2.76, p = .011, 95% CI for the mean difference = [.02, .14], d = 0.56; 10-year-olds (new: M = .60, repeated: M = .70), t(23) = 3.20, p = .004, 95% CI for the mean difference = [.04, .16], d = 0.65; and adults (new: M = .62, repeated: M = .70), t(31) = 3.96, p < .001, 95% CI for the mean difference = [.04, .12], d = 0.70. Similar results with the full scale are reported in the Supplemental Analyses file at https://osf.io/hw3gy.

Does prior knowledge protect against the illusory-truth effect?

Next, we examined whether the effect of repetition depended on participants’ prior knowledge. As shown in Table 2, repetition increased perceived truth for statements across all three knowledge levels: preschool, elementary school, and middle school. This was confirmed by a preregistered 2 (repetition: new, repeated) × 2 (statement truth: truth, falsehood) × 3 (knowledge level: preschool, elementary school, middle school) × 2 (age: 5-year-olds, 10-year-olds, adults) ANOVA on the proportion of statements that were rated as true. Similar analyses using the full rating scale are presented in the Supplemental Analyses file at https://osf.io/hw3gy.

First, our selection of stimuli on the basis of knowledge level was successful. Participants had the most knowledge about the preschool statements, followed by the elementary school statements, and then the middle school statements. This pattern was reflected in an interaction between statement truth and knowledge level, F(2, 154) = 112.72, p < .001, η_p² = .59. Participants were able to easily distinguish between true and false preschool statements (true: M = .89, 95% CI = [.85, .93]; false: M = .39, 95% CI = [.34, .43]) and could distinguish between true and false elementary school statements (true: M = .81, 95% CI = [.77, .85]; false: M = .53, 95% CI = [.49, .57]), but true and false middle school statements were rated similarly (true: M = .64, 95% CI = [.60, .69]; false: M = .66, 95% CI = [.62, .70]).

The three age groups did differ in their ability to distinguish the true and false statements at each knowledge level. As reflected by interactions between age and knowledge level, F(4, 154) = 3.72, p = .006, η_p² = .09, and statement truth by age by knowledge level, F(4, 154) = 7.54, p < .001, η_p² = .16, the 5-year-olds were less able to distinguish between true and false statements than the 10-year-olds and adults. This was particularly true for the preschool statements. As shown in Table 2, adults’ and 10-year-olds’ truth ratings were very similar for statements at each knowledge level.

Most importantly, repetition did not interact with knowledge level, either on its own, F(2, 154) = 0.20, p = .818, η_p² = .00, or in conjunction with age, F(4, 154) = 0.27, p = .894, η_p² = .01. As in prior research (Fazio, 2020; Fazio et al., 2015), prior knowledge did not protect against the illusory-truth effect. Repetition affected all statements equally.

To further confirm that the effect of repetition did not vary with knowledge, we conducted a preregistered 2 (repetition: new, repeated) × 2 (statement truth: truth, falsehood) × 3 (knowledge level: preschool, elementary school, middle school) ANOVA on the proportion of statements that were rated as true within each age group. The interaction between repetition and knowledge level was not significant for the 5-year-olds, F(2, 46) = 0.09, p = .915, η_p² = .00; the 10-year-olds, F(2, 46) = 0.09, p = .911, η_p² = .00; or the adults, F(2, 62) = 0.59, p = .559, η_p² = .02. The full results of the ANOVAs are presented in the Supplemental Analyses file at https://osf.io/hw3gy. As shown in Table 2, repetition increased adults’ truth judgments even for falsehoods that contradicted preschool-level knowledge (e.g., “A wasp is an insect that makes honey”; new: M = .23, repeated: M = .38), t(31) = 2.51, p = .018, 95% CI for the mean difference = [.03, .26], d = 0.44.

Model testing

Finally, we examined how well the knowledge-conditional and fluency-conditional multinomial models fitted the participants’ binary true/not true responses. As a reminder, the knowledge-conditional model assumes that participants rely on fluency only when they do not have relevant prior knowledge, whereas the fluency-conditional model assumes that participants sometimes rely on fluency, even when they have relevant prior knowledge (Fig. 1). Previous studies have found that adults’ responses are best fitted with a fluency-conditional model (Fazio et al., 2015).

Using multiTree software (Version 0.46; Moshagen, 2010), we estimated the model parameters by minimizing the distance between the observed and estimated response frequencies. That difference was measured by G², and thus smaller G² values indicate a better model fit. The null hypothesis is that the model fits the data, so p values less than .05 indicate a poor fit. As in prior work (Fazio et al., 2015), we placed theoretically informed constraints on the parameters to conserve degrees of freedom. The fluency parameter (F) varied across new and repeated items but was constrained to be the same for preschool, elementary school, and middle school facts and for truths and falsehoods. The knowledge parameter (K) varied across the different knowledge levels but was constrained to be the same for new and repeated items and for truths and falsehoods. Finally, the guessing parameter (G) was constrained to be equivalent for all statements. Thus, there were six free parameters—fluency for new items, fluency for repeated items, knowledge for preschool items, knowledge for elementary school items, knowledge for middle school items, and a guessing parameter. In the baseline models below, we allowed all six parameters to vary across the three age groups.

As expected, given previous research, the knowledge-conditional model provided a poor fit for the data, G²(18) = 54.43, p < .001. In contrast, the fluency-conditional model fit the data well, G²(18) = 22.41, p = .214. Because the analyses above indicated that fluency may affect each of the age groups similarly, we examined whether there was a decrease in model fit when we constrained the fluency parameters to be equivalent across the three age groups. The resulting model still provided a good fit to the data, G²(22) = 28.71, p = .153, and this constraint did not significantly reduce the model fit, ΔG²(4) = 6.30, p = .178. Thus, all three age groups were equally reliant on fluency to make their decisions. In contrast, constraining knowledge to be equivalent across the three age groups while allowing the fluency and guessing parameters to vary produced a model that significantly decreased the model fit, ΔG²(6) = 65.70, p < .001, and in fact no longer fit the data, G²(24) = 88.10, p < .001.

Table 3 shows the parameter estimates from the fluency-conditional model with the fluency parameters equivalent across the three age groups. Each parameter can be interpreted as the probability that the cognitive process contributes to the observed behavior. Importantly, the parameters varied as one would expect, providing further evidence for the model. First, participants were less likely to rely on their prior knowledge for middle school facts than for preschool facts. In addition, participants were more likely to rely on fluency for repeated statements than for novel statements. Finally, the younger children were less likely to rely on their prior knowledge than the older children and adults (likely because they had less prior knowledge).

Table 3.

Parameter Estimates for the Fluency-Conditional Model With the Fluency Parameters Equivalent Across the Age Groups

Parameter	5-year-olds	10-year-olds	Adults
F: new	.17 [.10, .24]	.17 [.10, .24]	.17 [.10, .24]
F: repeated	.33 [.27, .39]	.33 [.27, .39]	.33 [.27, .39]
K: preschool	.31 [.17, .44]	.88 [.80, .95]	.80 [.72, .88]
K: elementary school	.07 [−.06, .20]	.50 [.38, .63]	.58 [.47, .69]
K: middle school	.00 [−.12, .12]	.06 [−.06, .19]	.00 [−.10, .10]
G	.52 [.46, .58]	.56 [.48, .64]	.60 [.54, .67]

Note: Values shown in brackets are 95% confidence intervals. “F: new” refers to reliance on fluency for new statements; “F: repeated” refers to reliance on fluency for repeated statements; “K: preschool” refers to reliance on knowledge for preschool statements; “K: elementary school” refers to reliance on knowledge for elementary school statements; “K: middle school” refers to reliance on knowledge for middle school statements; and “G” refers to “guess ‘true.’”

Discussion

Repetition increased perceived truth across development. Five-year-olds, 10-year-olds, and college students were all more likely to judge repeated statements as true than novel statements. These results suggest that the connection between repetition and truth is learned at a young age. Instead of requiring a naive theory of fluency that is developed through reflection and metacognition, children learn the relation between repetition and truth implicitly through their interactions with the world around them. Before children are able to reflect on their internal feeling of familiarity or fluency and how it relates to the truth of a statement, children use repetition as a signal for truth.

These results fit with prior research suggesting that people connect repetition with truth because, in general, statements that we hear multiple times are likely to be true. Thus, when we are presented with a situation in which this correlation does not hold (e.g., repeated items are more likely to be false), our judgments change accordingly (Unkelbach, 2007). Our results demonstrate that, just like adults, young children are attentive to this connection between repetition and truth.

We also replicated previous findings suggesting that prior knowledge does not protect against the illusory-truth effect (Fazio et al., 2015; Fazio et al., 2019). Across all three age groups, repetition increased truth judgments equally for known statements and unknown statements. In fact, even college students who heard false preschool-level statements (e.g., “A wasp is an insect that makes honey”) twice were more likely to judge them as true compared with when they heard these statements only once.

Multinomial processing-tree models supported these two conclusions. For all age groups, the best-fitting model was one in which participants sometimes relied on fluency alone without consulting their prior knowledge. Thus, repetition can affect truth judgments even when participants have prior knowledge. In addition, the fluency-first model provided a good fit to the data even when the fluency values were restricted to be equivalent across the three age groups. Despite large developmental differences among 5-year-olds, 10-year-olds, and adults, all three age groups relied on fluency, familiarity, or cohesion similarly to make their truth judgments.

These findings fit with prior evidence that the illusory-truth effect is universal—occurring for all people and all stimuli. For example, a number of individual-difference measures—including fluid and verbal intelligence, need for closure, experiential and rational processing styles, preference for intuition and deliberation, and cognitive reflection—all fail to explain variation in the size of the illusory-truth effect across participants (De keersmaecker et al., 2020). In addition, repetition affects belief in political false-news headlines equally regardless of whether the headline supports or opposes the reader’s preferred candidate (Pennycook et al., 2018). Similarly, in this study, we found that repetition affects belief across development and prior knowledge. We conclude that the illusory-truth effect is a universal effect learned at a young age.

Supplemental Material

Fazio_OpenPracticesDisclosure_rev – Supplemental material for The Effect of Repetition on Truth Judgments Across Development

Supplemental material, Fazio_OpenPracticesDisclosure_rev for The Effect of Repetition on Truth Judgments Across Development by Lisa K. Fazio and Carrie L. Sherry in Psychological Science

Footnotes

Acknowledgements

We thank Taylor Boothby for her help in designing the stimuli for the experiment.

Transparency

Action Editor: D. Stephen Lindsay

Editor: D. Stephen Lindsay

Author Contributions

L. K. Fazio developed the study concept. Data collection was supervised by C. L. Sherry. Analyses were conducted by L. K. Fazio. Both authors contributed to writing the manuscript, with L. K. Fazio taking the lead role. Both authors approved the final manuscript for submission.

ORCID iD

Lisa K. Fazio

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