We’ve understood for centuries, maybe longer, that repetition breeds belief: ideas that we hear frequently repeated are far more readily accepted as truth than those we only hear once.

The Illusory Truth Effect

But it wasn’t until 1977 that this phenomenon actually entered the academic realm, subsequently dubbed the illusory truth effect. Here’s how it worked: a group of students were presented with a series of statements, and asked to rate how likely they thought each statement was to be true, from 1 to 7. Some of the statements were true and some false, but all of them were fairly obscure facts that few people were likely to know. Those same students were presented with another list of facts two weeks later, and then again two weeks after that. While some of the statements were different, there were some repeated false statements from earlier lists. The researchers found that, upon repetition, students were increasingly likely to rate those false statements as true.

Many subsequent studies have echoed this finding that repetition breeds belief. (This is apparently true even when you know the statement to be false at the outset—if you hear it over and over again, you start to question your original conviction and believe it anyway!)

Illusory Truth and Perceptual Fluency

The concept of illusory truth is related to the idea of perceptual fluency, which is an academic way to say that the easier it is for us to understand the idea being presented, the more likely we are to believe it. In this study, participants were asked to read various statements against various colored backgrounds, some easier and some harder to read. The statements that were easiest to read were also rated most likely to be true! 

Illusory truth is considered to be another aspect of perceptual fluency: the more often we hear an idea, the faster the associated neurons in our brains fire when presented with that idea. Repeated exposure therefore generates perceptual fluency.

You Can Only Pay Attention to So Much

This isn’t a bad thing–in fact, one might argue that it’s a necessary shortcut. The human brain gets bombarded with, according to one recent study, 34 gigabytes of information every day. (I don’t know about you, but I’m not terribly technical, so I don’t even have a concept of how big that number is.) We can’t possibly process that much information at once, so we have to make shortcuts, or biases, to determine where we’re going to place our attention.

This book breaks down these cognitive biases, and how it relates to illusory truth: given how much information our brains have to process in a given day, we can’t possibly question everything. (Imagine how much energy that would take!) So we’re biased to assume that statements are true. If we do question them, though, we tend to assume that if we’ve heard a statement before, it’s more likely true (and isn’t that the case, more often than not?) 

Illusory Truth and Affirmations

Ok, so let’s apply this. The self-help industry pushes the concept of “affirmations”: writing down positive statements about oneself and reviewing them on a regular basis. The concept is, the more often we review a statement, the more likely we are to grow to believe it. (This is also called meditation, by the way—repeatedly turning an idea over in your mind.)

The concept of illusory truth helps to explain why this is so powerful. If you can come to believe an oft-repeated esoteric statement of fact with no significance to your life, just by repetition (or if you can start to buy into someone else’s agenda for the same reason), can’t the same approach be used to reprogram your mind intentionally? I’d propose that this is why it’s so important to choose positive ideas with which to fill our minds. (And that’s why half of my podcasts are scripture meditations.) As the Apostle Paul says, “Finally, brothers and sisters, whatever is true, whatever is noble, whatever is right, whatever is pure, whatever is lovely, whatever is admirable—if anything is excellent or praiseworthy—think about such things” (Phil 4:8). 

I’d also propose that this is why positive self-affirmations can be so effective. Unlike external truths, we do have some control over who and what we become—hence the whole concept of the “self-fulfilling prophecy.” The more you say them, the more you believe them. The more you believe them, the more you will act in accordance with your new self-concept.

The Upshot

Illusory truth is just a cognitive bias, and it is neutral, in and of itself—it can work for, or against you. Be intentional about what you’re putting in your mind. Make sure it’s something you want to come to believe.