But that doesn't mean there's nothing we can do to protect ourselves against the illusion. A study in Cognition has found that using our own knowledge to fact-check a false claim can prevent us from believing it is true when it is later repeated. But we might need a bit of a nudge to get there.
The illusory truth effect stems from the fact that we process repeated statements more fluently: we mistake that feeling of fluency for a signal that the statement is true. And the effect occurs even when we should know better — when we repeatedly hear a statement that we know is wrong, for instance, like "The fastest land animal is the leopard". But Nadia Brashier at Harvard University and colleagues wondered whether asking people to focus on the accuracy of a statement could encourage them to use their knowledge instead, and avoid relying on feelings of fluency.
In the initial study, the team first asked 103 participants to read 60 widely-known facts, some of which were true (e.g. "The Italian city known for its canals is Venice"), and some of which were false (e.g. "The planet closest to the sun is Venus"). One group rated how interesting each statement was, while the other rated how true it was. Then in the second part of the study, both groups saw the same 60 statements along with 60 new ones — again a mixture of true and false — and rated their truthfulness.
Comment: See also: The illusion of truth: Believing something is true when it's not