Science suggests that frequently repeating a lie creates “the illusion of truth”

The techniques of propagandists work for good reason. Studies show that the more often we hear a statement, the more likely we are to believe it is true—regardless of the underlying facts.

Tom Stafford, a professor of psychology and cognitive science at the University of Sheffield and author of For argument’s sake: Evidence that reason can change minds, wrote in BBC Future that the “illusion of truth” is created from frequently hearing a statement repeated. Stafford points to a 2015 Vanderbilt University study showing that this illusion works even when the person hearing the statement is aware of a contradictory fact.

The study, published in the Journal of Experimental Psychology, asked 80 participants to judge whether or not a statement is true. In the first study, 40 participants were asked to rate how true a statement was on a six-point scale, whereas in the second, a different set of 40 participants were asked to simply state whether the statement was true or false. In both cases, repetition made a statement more likely to be categorized as true. This was the case even for statements that contradict well-known facts, such as, “Oslo is the capital of Finland,” (when in fact, Helsinki is the Finnish capital).

“The present research demonstrates that fluency can influence people’s judgments, even in contexts that allow them to draw upon their stored knowledge,” wrote the Vanderbilt study’s authors. Deciding a statement is untrue takes “a second, resource-demanding step,” write the authors and, rather than use this energy, it seems we’re naturally inclined not to question falsehoods.

Stafford argues that logically analyzing each new piece of information would take far too much time, and so it makes sense that we rely on repetition as a judgment shortcut. “Any universe where truth gets repeated more often than lies, even if only 51% vs 49% will be one where this is a quick and dirty rule for judging facts,” he writes.

But he also points out that, though repetition influences whether we regard a statement as true, so does truth. In the Vanderbilt study, true statements were still more widely believed than often-repeated false ones.

The idea that we’re not blind to the truth is heartening. Humans are perfectly capable of reasonable judgments, and can use logical capabilities to guard against the effects of repetition. But in an age characterized by competing political narratives and spin, there’s no room to be lazy about questioning the facts.

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