The Illusory Truth Effect is a cognitive bias in which people tend to believe that a statement is true if they have encountered it before. The phenomenon happens whether the interval between repetitions is minutes, weeks, or even months. Furthermore, the effect is independent of the source of the remarks and occurs even when participants are expressly informed that the source of the assertions is untrustworthy.
Also called the validity effect, the illusion of truth effect, or the reiteration effect, The illusory truth effect plays a role in how individuals process and recall information from their previous experiences. It also plays an important role in news media, advertising, social media, and political propaganda. It is one of the reasons why fake news spreads and misinformation retractions fail.
A key factor contributing to the Illusory Truth Effect is the ease of processing, or fluency, with which individuals can recall the information. When people encounter information repeatedly, they are more likely to process it more easily. This increased fluency often leads to a mistaken belief that the information is true, even if it is actually false or misleading.
The effect works because when people evaluate reality, they base their decision on whether the material matches their understanding or feels familiar.
The first condition makes sense because people compare new information to what they already know to be true and weigh the reliability of both sources. However, researchers observed that familiarity may overwhelm rationality — to the point where repeatedly hearing that a specific truth is incorrect can make it feel right.
Impact on Implicit Memory
Implicit memory plays a significant role in the Illusory Truth Effect. Unlike explicit memory, which deals with the conscious recollection of facts, implicit memory involves the unconscious influence of past experiences on one’s behaviour.
When individuals are exposed to a piece of information multiple times, it becomes ingrained in their implicit memory, shaping their cognitive processes and affecting their perceptions of truth.
One study on the effects of repetition frequency on the Illusory Truth Effect found that with each additional repetition, the perceived truthfulness of a statement incrementally increased. This shows that repeated exposure to information, whether factual or not, impacts one’s implicit memory and contributes to the Illusory Truth Effect.
Illusory Truth Effect Initial Study
The effect was named and defined for the first time based on the findings of a 1977 study at Villanova University and Temple University in which participants were asked to rate a series of trivial statements as true or false. Lynn Hasher, David Goldstein, and Thomas Toppino presented the same group of college students with lists of sixty plausible statements, some of which were true and some of which were false, on three separate occasions.
The second list was distributed two weeks following the first, and the third list was distributed two weeks afterwards. Twenty statements occurred on all three lists; the remaining forty entries on each list were unique.
Participants were asked how certain they were of the truth or falsity of statements about which they likely had little knowledge. For example,
“The gestation period of a giraffe is 425 days”
“One out of five people worldwide lack confidence in non-govermental organizations”.
On a scale of one to seven, participants were asked to rate their belief in the veracity of each statement. While participants’ trust in the truth of non-repeated assertions remained constant, it grew from the first to the second and second to third sessions. The researchers came to the conclusion that repeating a statement increases the likelihood that it will be perceived as true.
Initially, the truth effect was thought to occur only when people were extremely uncertain about a given assertion. Psychologists also anticipated that “outlandish” headlines would not have this effect, but new research demonstrates that the illusory truth effect is present with misleading news.
The findings of a 2015 study by Lisa K. Fazio, Nadia M. Brasier, B. Keith Payne, and Elizabeth J. Marsh called this premise into question. The study, published in the Journal of Experimental Psychology, suggested that the truth effect can influence participants who already knew the correct answer but were swayed to believe otherwise by the repetition of an untruth.
For example, when participants heard the statement “A sari is the name of the short plaid skirt worn by Scots” on multiple occasions, some of them were likely to believe it was true, even though these same people had no difficulty correctly answering the question “What is the name of the short pleated skirt worn by Scots?”
After replicating these findings in another experiment, Fazio and her colleagues attributed this strange phenomenon to processing fluency – the ease with which people comprehend statements. Repetition makes statements easier to comprehend (fluent) in comparison to new ones, prompting individuals to believe (often incorrectly) that they are more accurate, explained Fazio.
- De keersmaecker, J., Dunning, D., Pennycook, G., Rand, D. G., Sanchez, C., Unkelbach, C., & Roets, A. (2020). Investigating the Robustness of the Illusory Truth Effect Across Individual Differences in Cognitive Ability, Need for Cognitive Closure, and Cognitive Style. Personality and Social Psychology Bulletin, 46(2), 204–215
- Fazio, Lisa K.; Brashier, Nadia M.; Payne, B. Keith; Marsh, Elizabeth J. (2015). Knowledge does not protect against illusory truth. Journal of Experimental Psychology: General. 144 (5): 993–1002. doi:10.1037/xge0000098
- Hasher, Lynn; Goldstein, David; Toppino, Thomas (1977). Frequency and the conference of referential validity. Journal of Verbal Learning and Verbal Behavior. 16 (1): 107–112. doi:10.1016/S0022-5371(77)80012-1
- Hassan, A., Barber, S.J. The effects of repetition frequency on the illusory truth effect. Cogn. Research 6, 38 (2021)
- Unkelbach, C. (2007). Reversing the truth effect: Learning the interpretation of processing fluency in judgments of truth. Journal of Experimental Psychology: Learning, Memory, and Cognition, 33, 219–230