Home > Cognitive Bias, Metacognition > Unraveling the mechanism behind “a lie repeated a thousand times becomes truth”: A cognitive account

Unraveling the mechanism behind “a lie repeated a thousand times becomes truth”: A cognitive account

Lies are lying in TRUTH.gif

What is the boundary between lies and truths? I bet this question is among the first philosophical queries sprouted during our “younger and more vulnerable years” and is securely seated on the top of the list right next to “what is the purpose of life” and “is death a start or an end”. Take a moment to hark back to your teenage theory about truth and lie before cognitive psychologists swoop in and kill the romanticism like wiping the tender mist off the window pane…… You’ve done reminiscing? Ok, I’ll start.

Lies and truths do not seem to be that different, much like you might have concluded as a teenager. Despite of a difference in their objective compatibility with reality, both truths and lies are just information to be processed. In fact, lies could be seasoned to come off as more truthful, and the recipe is very simple— repetition. You might have heard the pop wisdom that “a lie that is repeated a thousand times becomes truth” at some point in your life. This actually has a well-founded cognitive basis.

Although there’s hardly any evidence that Goebbels ever said this… You get the idea, it’s pop culture! (To read a paper that delves deeper into this phenomenon, which concerns false information transmission in cyberspace, click here) (Note: Joseph Goebbels was a nefarious human being who was the Reich Minister of Propaganda of Nazi Germany. This blog in no way identifies with him or his views about political propaganda.)

Hasher, Goldstein, and Toppino first observed in 1977 that repeated exposures to an unfamiliar piece of information could increase perceived truth rating of that information, regardless of whether it was actually true or false. For example, if I tell you that “the only crustacean that has serotonergic pathways is lobster” with other statements and then give you a truth rating task, you are likely to rate the statement that I just made up about lobsters as true, more so than other statements that you haven’t seen before. This phenomenon, coined as the illusory truth effect, is present for all kinds of statements that range from trivia (e.g. The highest mountain in Venezuela is Pico Bolívar) to opinion (e.g. Early schooling should be permitted for families with special needs) (Dechêne, Stahl, Hansen, & Wänke, 2010). It is also quite robust, judging from the fact that it exists even when the repeated statements come from non-credible sources (Begg, Anas, & Farinacci, 1992).

An educated guess about your attitude right now.jpg

At this point, you must be on the edge of your seat with an itch to dive into the experimenters’ pool of subjects and be a data point that invalidates this very finding, because, how could this be? Even though the idea that repetition breeds truths is not entirely strange to us— it’s been around our pop culture for some time, it’s still hard to imagine people actually succumbing to the effect of repetition in a simple laboratory task. So, what is it about repetition that can sway our judgment towards “true”?

Turns out, the effective ingredient in this dose of repetition is likely high processing fluency. In plain words, information that is processed faster and with more ease is more likely to be judged as true, which was elegantly demonstrated by Reber and Schwarz in 1999. Reber and Schwarz artificially manipulated processing fluency by tinkering with the visual contrast between statements and their background, with green/yellow words against white background being the low processing fluency condition and dark blue/red words against white background being the high processing fluency condition.

Try this for yourself. Look at the image below. Do you feel that the words in dark blue/red almost “pop out” of the background but not the ones in yellow or green? (FYI: Quantitatively speaking, according to Reber and Schwarz, the processing speed of green/yellow words almost doubles that of dark blue/red against a white background. This was measured by comparing the time it took for people to identify letters that were written in these different colors).

Some colors don’t need vocal cords to sound convincing.PictureImadeInPages 🙂

It was observed that participants in the high visual contrast condition rated the statements to be true more frequently than those in the low visual contrast condition, which means that high processing fluency alone is sufficient to produce the illusory truth effect. Repeated exposure to information, however, as one of many avenues that could lead to higher processing fluency, is no longer necessary.

Yet, the fundamental problem persists. Be it repetition-induced processing fluency or just direct processing fluency, what does it have to do with truth judgment? To answer this question, let’s first look at how processing fluency is related to judgment in general.

Consider the following example. If people are divided into two groups and then asked to come up with 6 or 12 examples of their own assertive behaviors respectively, which group do you think would rate themselves as more assertive? (Hint: “less is more” applies here.)

I guess you’d think that more examples of assertive behaviors, which means more evidence, surely would mount to a judgment of higher general assertiveness. Yet there is a plot twist— our judgment is evidence-based alright, but our thought content (i.e. opinions and events that

The kind of math that doesn’t apply in psychology.jpeg

we could spell out) is not the only thing that gets weighted in judgment making. The metacognitive experiences, for example, the ease or difficulty experienced during the process of generating these thoughts, can also be interpreted and used as evidence to form judgments.

In the assertiveness case, as people exhausted their memory to get to 12 examples, they gradually experienced more difficulty than people who only needed to come up with 6. The unconscious detection and interpretation of this experienced difficulty led people to decide that they might not be very assertive in the first place. Why is it so hard to come up with 12 examples— because there aren’t that many to start with (Schwarz, Bless, Strack et al., 1991)!

Metacognitive experiences and judgment making is, therefore, bridged by the potential for these experiences to be interpreted. So, processing fluency, which is essentially the ease experienced during information processing, can also be “informative in its own right” (Schwarz, 2004). The illusory truth effect, then, could be viewed as the aftermath of people interpreting the high processing fluency experienced for repeated information and then attributing it to the truth of that information.

The next question is, why don’t we attribute high processing fluency to the falsehood of that information? Why is there a general tendency for people to interpret high processing fluency as an indicator of truth?


One possibility that unravels this mystery, as proposed by Unkelbach in 2007, is that this tendency to interpret truth from high processing fluency was acquired from our life experience. This is much like how we learned to pay attention to whatever the pointy end of an arrow is pointing at but have little interest for where the butt of the arrow sits.

Here’s how Unkelbach tested his idea. Participants were first exposed to 60 statements. Then, in what could be called an “association study phase”, participants were presented with some new statements, the processing fluency of which was manipulated by changing their visual contrast. In this phase, participants were asked to judge each statement as true or false and were given immediate feedback about the veridical truth status of each statement (i.e. telling participants which statement is actually false/true). Each statement of high visual contrast, which was processed more fluently, was tagged as false during feedback and low visual contrast as true. In this way, high processing fluency became associated with false statements.

The upshot of the experiment was that, in the final test phase, when the participants encountered again the 60 statements that they were exposed to in the very beginning of the experiment, they were more likely to rate these repeated statements as false as compared to statements that they hadn’t seen before— the illusory truth effect was successfully reversed.

“Truth” is now the third-wheel 🙁  (reversed illusory truth effect).screenshot.HarryPotter AndThePrisonerOfAzkaban

It appears that a new interpretation of processing fluency could be learned. This provides the possibility that the interpretation we have right now was picked up in life. In other words, metacognitive experiences like processing fluency can be interpreted to inform judgments, but how or in what direction it will be interpreted is dependent on what pattern is extracted from life. And this begs the question— how did life teach us that high processing fluency goes together with truth?

Unkelbach proposed that, in this world, there is an infinite number of lies but only a limited number of truths. Do you still remember the example trivia that I gave? “The highest mountain in Venezuela is Pico Bolívar”. Truth concerning the highest mountain in Venezuela can only be “Pico Bolívar”, but lies can be virtually anything.

I only present the picture of Pico Bolívar here, because pictures of the mountains that are not the highest mountain in Venezuela can take me a lifetime to collect.jpg

I can easily create false information about the highest mountain in Venezuela to fill 1000 GB storage if need be, but I can hardly come up with more than one truth in this respect. As a result, the same truths are more likely to be encountered frequently than are lies, which have too many versions and too little practical values to be repeated again and again to afford high processing fluency (Unkelbach, 2007). Truth, therefore, becomes associated with high processing fluency.

(If you are not satisfied with this practical explanation and are interested in a more philosophical account concerning “how mental systems believe”, which talks about Spinoza’s idea about how understanding and acceptance are one and the same, and truth is the default consequence of understanding, click here.)

At this point of the blog, I could finally say that the mechanism underlying the illusory truth effect is likely as follows:

Based on our life experience that truths are more likely to have high processing fluency, we unconsciously infer that fluently processed information is likely to be truth. Or, in a more figurative light, lies are like hitchhikers who can board an express that was not designed for them, and high processing fluency afforded by repetition will be their ticket.

Even though we now have one pretty complete and probable account of the illusory truth effect, there’s still a lot that could be said about this effect and its mechanism, which seems to underlie a whole family of cognitive biases.

A question that is both literal and rhetorical.jpg

For instance, the low processing fluency of non-native speakers’ speech was suggested to account for why non-native speakers are taken as less credible (Lev-Ari & Keysar, 2010); on the contrary, sentences that rhyme (e.g. an apple a day keeps the doctors away) are deemed as more truthful, which is a phenomenon termed the rhyming-as-reason effect, is probably because rhyming sentences are more easily processed. And I personally feel that my barely legible handwriting is the true culprit behind my waning scores in exams with essay questions. Can you come up with an example that might be caused by a similar mechanism?

Hopefully, after reading this blog, you’ve gained a new perspective. And things that originally seemed counterintuitive to our theories of how we perceive and make sense of the world can now be appreciated and understood. While we intuitively believe that we are animals of rationality who make decisions following the tracks of reason, we need to recognize that judgment making is not solely a game of the “mind”; judgments are tied as much to the things that we are aware of (i.e. thoughts, intentions, knowledge and etc.) as to the things that we are not (i.e. unconscious interpretation of metacognitive experiences).




Begg, I. M., Anas, A., & Farinacci, S. (1992). Dissociation of processes in belief: Source recollection, statement familiarity, and the illusion of truth. Journal of Experimental Psychology: General, 121(4), 446–458. https://doi.org/10.1037/0096-3445.121.4.446

Dechêne, A., Stahl, C., Hansen, J., & Wänke, M. (2010). The truth about the truth: A meta-analytic review of the truth effect. Personality and Social Psychology Review, 14(2), 238–257. https://doi.org/10.1177/1088868309352251

Hasher, L., Goldstein, D., & Toppino, T. (1977). Frequency and the conference of referential validity. Journal of Verbal Learning and Verbal Behavior, 16(1), 107–112. https://doi.org/10.1016/S0022-5371(77)80012-1

Lev-Ari, S., & Keysar, B. (2010). Why don’t we believe non-native speakers? The influence of accent on credibility. Journal of Experimental Social Psychology, 46(6), 1093–1096. https://doi.org/10.1016/j.jesp.2010.05.025

Reber, R., & Schwarz, N. (1999). Effects of perceptual fluency on judgements of truth. Consciousness and Cognition, 8(3), 338–342. https://doi.org/10.1006/ccog.1999.0386

Schwarz, N. (2004). Metacognitive experiences in consumer judgement and decision making. Journal of Consumer Psychology, 14(4), 332–347. http://doi.org/10.1207/s15327663jcp1404_2

Schwarz, N., Bless, H., Strack, F., Klumpp, G., Rittenauer-Schatka, G., & Simons, A. (1991). Ease of retrieval as information: Another look at the availability heuristic. Journal of Personality and Social Psychology, 61(2), 195–202. https://doi.org/10.1037//0022-3514.61.2.195

Unkelbach, C. (2007). Reversing the truth effect: Learning the interpretation of processing fluency in judgments of truth. Journal of Experimental Psychology: Learning Memory and Cognition, 33(1), 219–230. https://doi.org/10.1037/0278-7393.33.1.219



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