Have you ever noticed how a vaguely familiar statement, something you remember hearing, makes you think “there has to be something to it” or “this has to be true, I have heard it before”? This is what social psychology calls the “illusory truth effect”, which means that a person attributes higher credibility and trustworthiness to information to which they have been exposed before. In a nutshell, repetition makes information more credible and trustworthy. Frequency, it seems, serves as a “criterion of certitude”.
What is really interesting about this is that this effect has not only been tested for plausible information but even for statements initially identified as false. And the effect is immediate: already reading a false statement once is enough to increase later perceptions of its accuracy. An experiment carried out by researchers in the US showed the truth effect even for highly implausible, entirely fabricated news stories. The researchers further were able to show that the effect holds true even if participants forgot having seen the information previously. Even if participants disagree with information, repetition made it more plausible.
But why does this effect exist? Research gives us several answers to this. First, familiarity with the information leads to faster processing of that information. Second, recognition of information, and coherency of statements with previous information in a person’s memory, affect our judgement. Third, there is a learned effect that faster processing of information and truthfulness of information can be positively correlated.
When it comes to misinformation and fake news, the importance of this effect cannot be stressed enough. Even warnings by fact-checkers or experts cannot counter it; the only way of protecting yourself and others from misinformation is to avoid sharing any piece of dubious information. So, one of the most important rules we identified as part of our guidelines for information hygiene is simply if in doubt, don’t share.
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Unkelbach, C., Koch, A., Silva, R. R., & Garcia-Marques, T. (2019). Truth by Repetition: Explanations and Implications. urrent Directions in Psychological Science, 28(3), 247-253.