The illusory truth effect was first identified in a 1977 study by psychologists Lynn Hasher, David Goldstein, and Thomas Toppino. They found that repetition increases the perceived truthfulness of statements, even when people know the information is false or have prior knowledge to the contrary.

This effect is powerful because it operates subconsciously. Repetition makes information easier to process (a phenomenon called “fluency”), and our brains often mistake this ease for accuracy or truth.

Examples

• Political propaganda and advertising often rely on this effect, repeating slogans or claims until they are accepted as fact.
• Urban legends and misinformation spread online can become widely believed simply through frequent sharing.

The illusory truth effect highlights the importance of critical thinking and fact-checking, especially in the age of social media.

Being aware of this bias can help guard against believing false or misleading information just because it is familiar.