Why Repetition Makes Lies Stick: The Illusory Truth Effect

“Why do they keep repeating these lies?!” It’s called the illusory truth effect, and frankly, it’s kind of terrifying.

The Dangerous Power of Hearing Things Twice

Our brains are lazy, efficient machines. They’re constantly looking for shortcuts. One of the sneakiest shortcuts they take involves repetition. When we hear a statement multiple times, even if it’s pure garbage, we’re more likely to believe it’s true compared to something we’re hearing for the first time. This is happening all around you, all the time, in everything from political messaging to junk science claims about some supplements.

This phenomenon, the illusory truth effect, pops up with consumer ads, political blather, and everyday rumors. It works whether you hear something just minutes apart, or after weeks or even months. It’s been replicated countless times and across different types of information, like trivia, health claims, product pitches, opinions, and yes, fake news headlines. The effect isn’t just for things we don’t know anything about either; it can happen even when you possess knowledge that contradicts the statement. Think about that for a second: Hearing something repeated can make you believe it, even if you know, deep down, it’s wrong.

Why Does This Keep Happening? The Brain’s Efficiency Hack

The most accepted explanation for this mess boils down to something called processing fluency. Basically, when your brain has encountered a piece of information before, it processes it more easily the next time around. It feels smoother, more familiar. And because, in a generally truthful world, things that are easier to process are often true, our brains use that feeling of ease – that fluency – as a stand-in cue for truth. It’s a mental shortcut, and it works pretty well most of the time, making it a reasonable, “cognitively inexpensive” strategy.

This isn’t just about repetition either. Anything that makes information easier to process can give it a boost in perceived truthfulness. Like statements presented in an easy-to-read font, for example (NOT THIS FONT). The brain just feels that “ease” and tags it with a “looks true” sticker.

Who’s Affected and What Slows It Down?

Here’s the really unsettling part: The illusory truth effect appears to be pretty robust. It doesn’t seem to rely much on individual differences in things like cognitive ability (how smart you are), your need for simple answers, or whether you tend to think intuitively versus analytically. Even people who are generally skeptical might only be slightly less susceptible. This suggests it’s a pretty basic cognitive process. Studies show it happens for older adults too.

However, it’s not completely bulletproof. The strength of the effect does seem to diminish over time as the delay between repetitions gets longer. The biggest jump in perceived truth comes from the very first time you hear something and then hear it again. After that, each additional repetition adds a smaller increase.

Also, how you process the information initially can make a difference. If you’re just passively reading something (a “low-involvement” task), the effect might be stronger. But if you’re actively engaged, like trying to figure out if something is a fact or an opinion, or acting as a fact-checker (and you have the knowledge to do it), that deeper processing can reduce or even eliminate the effect. One interesting finding is that if people encode opinions specifically as opinions, this can protect against the illusory truth effect, sometimes even reversing it for general opinions. So, if you recognize something is just a subjective take, repetition might not boost its perceived truth.

While some early work suggested the effect might not happen for extremely implausible statements, later research argues that repetition still increases your internal belief in those statements. You just might not see that increase on a rating scale if the statement is already viewed as basically zero truth, creating an “inverted U-shaped curve” where statements in the middle range of plausibility show the biggest observable effect. Basically, once something is seen as utterly ridiculous, repetition might not visibly make it “more true” on a scale, but the underlying mental tag might still shift slightly.

And warnings? Forget it. Telling people something might be false or warning them about the effect itself can reduce it, but it won’t make it disappear entirely.

The Real-World Disaster Zone

This is where it gets hairy. The illusory truth effect is a core mechanic exploited by anyone trying to sell you something, whether it’s a product, an ideology, or a politician. It’s a tactic used by propagandists to make their messages stick, regardless of whether they are accurate. Simply repeating something, even if it’s wrong, can increase belief.

In the age of social media, where information zips around and gets repeated constantly, the impact of this effect is significantly amplified. It helps explain why fake news can gain traction; prior exposure increases the perceived accuracy of fake news headlines, even if they’re implausible or politically charged. It even seems that seeing fake news repeated might make people feel less unethical about sharing it themselves. This effect, where familiarity can seemingly trump rationality, is a serious problem.

The Bottom Line

The illusory truth effect is a powerful, pervasive cognitive quirk. Our brains mistake familiarity for truth because it’s an efficient shortcut. This makes us vulnerable to repeated misinformation, propaganda, and advertising claims, regardless of whether we have the knowledge to know better. While deeper processing and recognizing something as opinion can offer some protection, the fundamental vulnerability remains.

In a world saturated with information, much of it intentionally misleading, understanding this effect offers some insights. Because while facts might outweigh opinions when opinions are recognized as such, simple repetition, tragically, makes almost anything sound a little more like the truth.

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