Joseph Goebbels, minister of propaganda for the Nazi German government of the Third Reich, understood the power of repeating falsehoods. “If you tell a lie big enough and keep repeating it,” he asserted, “people will eventually come to believe it.” This phenomenon, pervasive in contemporary politics, advertising, and social media, is known in cognitive psychology as the “illusory truth effect.”
Though multiple studies have found that repeated statements seem more truthful than novel ones, the illusion was thought to be limited to uncertain statements, or those in which people had no other information available, such as prior knowledge.
A recent study published in Psychonomic Bulletin & Review indicates that, contrary to accepted knowledge, belief in all statements, be they plausible or implausible, increases with repetition.
Psychologist Lisa Fazio of Vanderbilt University, in collaboration with David Rand of the Massachusetts Institute of Technology and Gordon Pennycook of the University of Regina, Canada, set out to determine whether the illusory truth effect occurs across levels of plausibility, or whether it applies only to ambiguous statements. To find out, the researchers used computational simulations combined with a large online study, completed via Amazon’s Mechanical Turk large-scale testing system.
Five hundred and three participants evaluated 80 statements, designed to cover the full range of plausibility, from definitely false to definitely true. Examples of highly implausible statements included “Elephants weigh less than ants,” and “The Earth is a perfect square.” Highly plausible statements included “The Sistine chapel's ceiling was painted by Michelangelo,” and “Most Americans have ridden in a vehicle of some sort.”
The experiment started with an “exposure phase,” in which 40 of the 80 statements were presented individually to participants, who simply indicated how interesting each statement was on a scale of 1 to 6. Participants then began the “truth rating phase,” in which they had to judge if each of the 80 statements (half of which they saw previously in the exposure phase) were true or not true. The experimenters informed participants that some of the statements were true and others false, and that some of the statements would be repeated from the prior task.
As predicted, the results showed that repeated statements were more likely to be rated as true than novel statements. Further, even though the illusory truth effect was much more easily observed in the middle of the plausibility spectrum than at either extreme, the data did not suggest a significant asymmetry in the relationship between plausibility and the magnitude of the illusory truth effect. In other words, the results were consistent with a consistent boost to belief across all levels of plausibility.
The implications for daily life, where consumers of news and products are often repeatedly exposed to both plausible and implausible falsehoods, is that even patent lies may slowly become more credible, provided enough repetition. Considering this vulnerability, it becomes critically important to not repeat falsehoods, even while we attempt to debunk them—lest we legitimize lies by reiteration itself.