How does information's repetition affect its believability?

UCL and MIT neuroscience professor Tali Sharot discusses a mistake we can make when we're exposed to the same information repeatedly

When I was a kid, most of my information about the world came straight from trusted sources: The PBS NewsHour, The Washington Post, and The New York Times. My parents subscribed to the Post and the Times, and every evening we’d watch the NewsHour together during or after dinner. It was a simpler time.

Fast forward to today, and my information diet looks wildly different. Now, I find myself frequently scrolling through LinkedIn, X, BlueSky, Threads, and Instagram. These platforms aggregate content for me from outlets like The New York Times, PBS, and The Washington Post but they also mix in a flood of updates from friends, colleagues, acquaintances, and even celebrities. In this new media landscape, it’s easy to lose track of where I’ve heard something—whether it came from a credible news source or someone who might have been misinformed.

There are many reasons this is a bit scary, but one relates to a psychological bias in the way we process information that we hear over and over again. That is the focus of today’s Q&A. 

But before we dive in, I have a bit of good news to share, along with a few hand-picked listens and reads I think you’ll enjoy…

Good News

Earlier this month, Choiceology with Katy Milkman was named an official selection at #BrandStorytelling2025, which is part of the Sundance Film Festival! We’re over the moon about this honor! Thank you for all of your support. If you’ll be in Park City for Sundance this year, please check out the brand storytelling panel and give three cheers for Choiceology. 

This Month’s Recommended Listens and Reads

• A Hero’s Journey: Our Choiceology season finale might be my favorite episode ever! Backed by fascinating research, it explores how reframing your life story as a classic Hero’s Journey can yield surprising benefits.

• Trying to Quantify Everything is Hurting our Decisions: This Bloomberg piece delves into new research I co-authored, revealing the outsize emphasis our decisions place on anything that’s quantified (e.g., the number of ratings a product has on Amazon) over qualitative factors (e.g., the product’s star rating or written reviews).

• Love Factually: Behavioral scientists Eli Finkel and Paul Eastwick host the witty and evidence-based new podcast Love Factually. Each episode analyzes a different romantic comedy—discussing its plot and what it gets right and wrong about the science of relationships. 

• Why and How to Change Your Exercise Routine: This Time feature explains how and why to break out of stale workout routines and build more satisfying ones and includes practical tips from my research.

Q&A: What Happens When We Encounter the Same Information Repeatedly?

In this Q&A from Choiceology, UCL and MIT neuroscience professor Tali Sharot discusses her research exploring a mistake we can make when we’re exposed to the same information repeatedly.

Me: First, could you describe “the illusory truth effect”?

Tali: If you hear something repeatedly, you're more likely to believe it regardless of whether it's true or if it's false. That's one reason that we believe things that are not true. A lot of people believe that you use 10% of your brain or that vitamin C can prevent the common cold. So the more you hear it, the more you believe it.

Me: What’s your favorite classic study that illustrates the illusory truth effect? 

Tali: I think maybe the first study is the best to illustrate it. The first study was published in 1977. They gave people 60 different statements. Some of them were true, and some of them were not, and 20 of them were repeated across three weeks, and the others were not repeated. What they found is that those statements repeated at least once were more likely to be believed.

So that's the first demonstration. But since then, this illusory truth effect has been shown many times. It's been shown in different populations, different gaps of time between the first time and the second time you hear it. So it's a very, very strong effect.

Me: Why is it that when I see or hear the same statement multiple times, I am more likely to believe it's true?

Tali: There's probably a few reasons. One reason is that when you hear something again and again, your brain processes it less and less. The first time you hear something absolutely new, like for example: “a shrimp's gut is in its head,” your brain has a lot to process. It maybe comes up with an image of a shrimp or the last time you ate a shrimp. So your mind does a lot of processing.

But the second time I tell you a shrimp's gut is in its head, the brain doesn't process it as much. And what happens when we process something less? It feels more familiar. It's less surprising. And we're used to familiar things being true. And so the result is that you're more likely to accept something the more familiar it is – the “truthier” it is. We don't stop to think about it. We've heard it before, the brain doesn't respond, and we just accept it as it is.

Now, a related reason is that we're quite good at remembering what we've heard before, but not necessarily where we've heard it. So you can hear statements from a lot of different places, and some of the sources can be quite dodgy, but you don't necessarily remember what the source was. So it's harder for you to figure out, "Well, I've heard this before, but was it a reliable source, or wasn't it a reliable source?"

Me: That’s fascinating, and this phenomenon fits into the heuristics and biases literature because it seems like familiar things probably are more likely true than new things, on average. It's just that this is going to lead us astray in situations, particularly where someone is deliberately trying to mislead us or where there's an often-repeated rumor that isn't true. Could you describe your recent research suggesting that the illusory truth effect can drive the spread of inaccurate information?

Tali: It's been shown so many times that things that you've heard more than once, you believe more. And so we thought, "Well, if you believe it more, are you going to share it more?" Because it turns out there's a lot of research that shows that people actually want to share true information. Yes, people sometimes go online to share misinformation. There are mal-agents. But most of us: we want to share true information. So we thought, "Well, let's see if we show people statements more than once, not only will they believe it more, they would want to share it more?"

So we did something quite simple. We showed people 60 different statements. We actually did two experiments. One experiment was all health statements. The other experiment was really a combination of statements from history and biology and so on. Half of the statements were repeated, and half were not repeated.

Me: How were they repeated? Was it just in the course of taking a survey experiment, or were they repeated over the course of time?

Tali: It was all in a short amount of time. It was all within one hour.  Next, for each statement, we asked two questions, and the order was random. Either we ask you how accurate it is first, or we ask you, "Do you want to share it?" And we found that statements that were repeated more than once, people believed them more, and they wanted to share them more. And the reason that people shared repeated statements more was because they believed those statements were more accurate.

Me: That’s fascinating.  Do you have advice for people on how they can try to avoid making mistakes related to the illusory truth effect now that they're aware of it?

Tali: The best way is: check the source. If something feels a little bit suspicious, check it out. If it's not important, it's not important. But if you're going to act based on the information, it's good to take a few seconds to just Google it. See: do you get hits from reputable sources?

Katy: So, what you're saying is once we start to understand that there are biases that can contort how well we assess the truthfulness of information, that should make us more skeptical of any information that we might instinctively want to believe. And so if we can just be a bit more skeptical generally, that's going to be protective, not just against the illusory truth effect, but probably against a whole range of biases in the way we judge what's accurate.

Thank you for the really interesting research you've done and for telling us about the illusory truth effect. I really appreciate it.

Tali: Thanks for having me. 

This interview has been edited for clarity and length.

To learn more about Tali’s work, listen to the episode of Choiceology where we dig into the illusory truth effect or check out her wonderful book, LOOK AGAIN: The Power of Noticing What Was Always There.

That’s all for this month’s newsletter. See you in December!

Katy Milkman, PhD

Professor at Wharton, Host of Choiceology, an original podcast from Charles Schwab, and Bestselling Author of How to Change

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