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What is Sleeper Effect?


During World War II, every nation produced propaganda movies. These were devised to fill the population, especially soldiers, with enthusiasm for their country and, if necessary, to bolster them to lay down their lives. The U.S. spent so much money on propaganda that the war department decided to find out whether the expense was really worth it. A number of studies were carried out to investigate how the movies affected regular soldiers. The result was disappointing: they did not intensify the privates’ enthusiasm for war in the slightest. 

Was it because they were poorly made? Hardly. Rather, the soldiers were aware that the movies were propaganda, which discredited their message even before they were rolling. Even if the movie argued a point reasonably or managed to stir the audience, it didn’t matter; its content was deemed hollow from the outset and dismissed. 

Nine weeks later, something unexpected happened. The psychologists measured the soldiers’ attitudes a second time. The result: whoever had seen the movie expressed much more support for the war than those who had not viewed it. Apparently, propaganda did work after all! 

The scientists were baffled, especially since they knew that an argument’s persuasiveness decreased over time. It has a half-life like a radioactive substance. Surely you have experienced this yourself: let’s say you read an article on the benefits of gene therapy. Immediately after reading it you are a zealous convert, but after a few weeks, you don’t really remember why. More time passes until, finally, only a tiny fraction of enthusiasm remains. 

Amazingly, just the opposite is true for propaganda. If it strikes a chord with someone, this influence will only increase over time. Why? Psychologist Carl Hovland, who led the study for the war department, named this phenomenon the sleeper effect. To date, the best explanation is that, in our memories, the source of the argument fades faster than the argument. In other words, your brain quickly forgets where the information came from (e.g. from the department of propaganda). Meanwhile, the message itself (i.e., war is necessary and noble) fades only slowly or even endures. Therefore, any knowledge that stems from an untrustworthy source gains credibility over time. The discrediting force melts away faster than the message does.

In the U.S., elections increasingly revolve around nasty advertisements, in which candidates seek to tarnish each another’s record or reputation. However, by law, each political ad must disclose its sponsor at the end so that it is clearly distinguishable as an electioneering message. However, countless studies show that the sleeper effect does its job here, too, especially among undecided voters. The messenger fades from memory; the ugly accusations persevere. 

I’ve often wondered why advertising works at all. Any logical person must recognise ads for what they are, and suitably categorise and disqualify them. But even you as a discerning and intelligent reader won’t always succeed at this. It’s quite possible that, after a few weeks, you won’t remember if you picked up certain information from a well-researched article or from a tacky advertorial.

How can you thwart the sleeper effect? First, don’t accept any unsolicited advice, even if it seems well meant. Doing so, you protect yourself to a certain degree from manipulation. Second, avoid ad-contaminated sources like the plague. How fortunate we are that books are (still) ad-free! Third, try to remember the source of every argument you encounter. Whose opinions are these? And why do they think that way? Probe the issue like an investigator would: cui bono? Who benefits? Admittedly, this is a lot of work and will slow down your decision making. But it will also refine it.

Alternative Blindness – WHY IT’S NEVER JUST A TWO-HORSE RACE

Similar Biases:
Primacy and Recency Effects – WHY FIRST IMPRESSIONS DECEIVE


The above article is from the book The Art of Thinking Clearly by Rolf Dobelli. The article is only for educational and informative purposes to explain and understand cognitive biases. It is a great book, definitely worth a read!