Why Repeated Falsehoods Start To Feel True — The Science Of The Illusory Truth Effect

People often hear the claim that we use only about 10% of our brains. It sounds scientific, but it's a myth. Brain activity shifts with different tasks, and over time we engage nearly all regions of the brain. Yet surveys show many people — including large numbers of teachers — still accept the 10% story as fact.

How Repetition Warps Perception

One major reason falsehoods gain traction is repetition: the more often we encounter a claim, the more likely we are to judge it as true — even when objective evidence contradicts it. Psychologists call this the illusory truth effect, and it helps explain why misinformation spreads and sticks in the digital age.

“When we're exposed to a piece of information repeatedly, it seems truer than the first time we heard it,”

— Sarah Barber, associate professor of psychology, Georgia State University.

What the Research Finds

Numerous experiments show that repeated exposure — on social media, television, in conversation, or elsewhere — makes false claims feel more legitimate. Barber and a colleague reported in a 2021 Cognition Research paper that the largest jump in perceived truth occurs on the second encounter with a statement. After that, each additional repetition nudges perceived credibility upward, though the effect size diminishes.

Other studies, such as work by Shauna Bowes and Lisa Fazio, show the illusory truth effect influences belief in conspiracy theories as well as trivial facts. Importantly, neither a person’s predisposition toward conspiratorial thinking nor their tendency to reflect deeply eliminates the effect. Even reflective, rational people become slightly more accepting of repeated false claims.

Why Familiarity Feels Like Truth

The most commonly cited explanation is processing fluency: information we've seen before is easier for the brain to process, and the mind takes that ease as a cue to truth. From an evolutionary perspective, repetition via word of mouth often signaled reliability; in today’s information environment, however, this heuristic can mislead us.

Practical Steps To Reduce Vulnerability

Knowing about the illusory truth effect helps, but it doesn't eliminate the phenomenon. Here are practical defenses:

• Limit exposure to platforms and feeds that frequently circulate dubious claims.
• Pause before sharing: take a moment to check a credible fact-checking source when a sensational claim appears.
• Curate your feed: follow reputable outlets and diversify information sources to reduce repeated contact with the same false claims.
• Use tools: browser extensions and fact-checking services can flag repeated or debunked content.

On a larger scale, researchers and experts call for social platforms to reduce the amplification of false content and to elevate accurate reporting. As Shauna Bowes puts it:

“As long as algorithms are flooding our social media feeds with false content, we’re all vulnerable.”

Repetition doesn't usually convert outright disbelief into certainty — but it does make false claims feel less implausible. Awareness, deliberate exposure management, and better platform moderation are the most practical defenses we currently have.