The illusory truth effect is the tendency for any statement that is repeated frequently—whether it is factually true or not, whether it is even plausible or not—to acquire the ring of truth. Studies show that repetition increases the perception of validity—even when people start out knowing that the information is false, or when the source of the information is known to be suspect.
How the Illusory Truth Effect Works
When it comes to human judgment, we are influenced by more than just the informational value of content. Among other factors, we are swayed by our experience of information processing. Repeated statements, whether they are factually true or false, are easier to process—they create processing fluency, which lends them validity.
The illusory truth effect does not hinge on whether the repetitions occur moments apart or weeks apart. Above and beyond the declarative information in a statement, processing ease is itself a piece of information we use to evaluate the truth of claims.
We infer truth from fluency of processing because, in the natural world, truth and fluency are correlated. Processing fluency is so equated with the truth that the illusory truth effect can occur with other facilitators of fluency in the absence of repetition. For example, studies find that information presented in easy-to-read fonts is more often rated as true than the same information presented in low-contrast fonts.
The illusory truth effect is such a robust phenomenon that it operates independently of cognitive ability. Neither differences in cognitive ability, in need for closure, nor in cognitive thinking style influence the power of repeated statements to appear true. An analytical thinking style is no protection, and a need for cognitive closure is not a facilitator.
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