During World War II, every nation employed propaganda to rally the masses, particularly soldiers, to fight for their country. These films, intended to boost morale and encourage soldiers to lay down their lives for a noble cause, were essential to wartime efforts. The U.S. government, spending millions of dollars on these films, eventually questioned whether this substantial investment was paying off. To find an answer, they initiated a series of studies to assess the effectiveness of propaganda on regular soldiers.
The findings were initially disheartening. Soldiers who watched these propaganda films showed no increased enthusiasm for war. The immediate conclusion? The films weren’t convincing enough. However, this reasonable conclusion failed to account for a peculiar twist that would eventually redefine the understanding of persuasive messaging.
The Dismissal of Propaganda: Why It Didn’t Work At First
During World War II, nations across the globe invested heavily in propaganda films, hoping to inspire their populations, especially soldiers, to embrace the war effort with enthusiasm. The U.S. government, in particular, devoted vast sums of money to producing films designed to elicit patriotic fervor, bolster morale, and encourage soldiers to fight with zeal. The assumption was that these films would effectively promote the cause and inspire soldiers to fight for their country, even to the point of sacrificing their lives.
However, the initial results were far from encouraging. When soldiers were exposed to these propaganda films, their support for the war effort increased little to no. This was puzzling to the researchers conducting the studies. How could such a well-funded, carefully crafted campaign fail to galvanize soldiers, who were arguably the most important audience?
The issue was not with the quality of the films themselves. In many cases, these films were expertly made, with high production values and compelling narratives. Rather, the failure could be attributed to the soldiers’ awareness of the films’ true purpose. The soldiers were fully aware that these films were propaganda—intended to manipulate them into supporting the war effort. The moment the soldiers recognized the films as tools of persuasion, their defenses went up. They mentally categorized the content as biased and manipulative and dismissed it.
Propaganda works best when it is perceived as neutral or factual. The soldiers’ skepticism toward the films stemmed from their understanding that they were being targeted for emotional manipulation. Despite the compelling arguments, stirring images, and heroic portrayals of war, they could not shake the feeling that they were being sold a message rather than asked to consider an objective truth. This awareness of manipulation caused them to reject the films, making their persuasive power null and void in the immediate term.
The Unexpected Twist: A Change in Attitude Over Time
Despite the films’ initial failure to alter soldiers’ attitudes, something remarkable occurred in the following weeks. After nine weeks, researchers revisited the soldiers to reassess their views on the war. The surprising result was that those who had viewed the propaganda films expressed much more support for the war effort than those who had not.
At first glance, this might seem counterintuitive. If the films failed to create an immediate emotional response and were dismissed outright as propaganda, why would they have any lasting effect? Normally, the influence of persuasive messages decreases over time. People forget details, lose interest, and move on. Yet, in this case, the opposite occurred. Instead of the soldiers’ attitudes waning, their support for the war seemed to grow stronger as time passed.
The key insight here is that time uniquely affected the soldiers’ responses. While the content of the films was initially dismissed due to their perceived manipulation, over time, the soldiers’ memories of the films began to lose their context. They no longer saw the films as propaganda; instead, they remembered only the messages and themes conveyed. In other words, the films’ discrediting force—being identified as propaganda—faded, while the persuasive message that the war was noble and necessary remained in the soldiers’ minds.
This phenomenon was both unexpected and profound. It demonstrated that persuasive messages can have an enduring effect even if initially rejected. The longer the delay between exposure and attitude change, the more potent the effect seemed to be, leading to a reassessment of how persuasive messages work over time.
The Birth of the Sleeper Effect
Psychologist Carl Hovland, who led the U.S. government’s research into propaganda during World War II, coined the term “sleeper effect” to describe this phenomenon. The sleeper effect refers to the delayed influence of a persuasive message, where its impact increases over time, even though the message’s source loses its credibility.
In simple terms, the sleeper effect suggests that we forget the source of the information more quickly than we forget the content of the message itself. For example, we may encounter a persuasive argument, and although we are initially aware of the source’s potential bias or agenda, this awareness fades over time. What remains is the argument or the message itself, which can continue to influence our attitudes or beliefs long after the source has been forgotten.
In the case of propaganda films, the soldiers were aware of the manipulative intent behind the messages. However, their memory of the films’ source—the war department—diminished as time passed. What remained were the persuasive arguments: the idea that the war was a noble cause worth fighting for. Over time, the soldiers began to internalize these arguments, and their support for the war increased despite their initial skepticism toward the films.
This groundbreaking discovery contradicted the prevailing understanding that persuasive messages lose power over time. The sleeper effect showed that, in some cases, time works in favor of the message, allowing it to resonate more deeply as the context fades. This insight has profound implications for understanding how persuasion works in wartime propaganda and all forms of communication.
The Sleeper Effect in Modern Advertising and Politics
The sleeper effect has continued to be a powerful force in modern-day advertising and political campaigns. While propaganda in the traditional sense may be less common, the principles of persuasion and influence remain at the heart of contemporary media. Political ads, in particular, have become infamous for their negative content, where candidates aim to tarnish their opponents’ reputations rather than promote their virtues.
Despite the transparency of political ads—where the sponsor is identified at the end—these ads still profoundly impact voters. The negative claims about a candidate or opponent can linger in voters’ minds, even when they forget who sponsored the ad. This is where the sleeper effect comes into play. As the viewer forgets the message’s source, the negative portrayal of the opponent persists. Over time, the influence of these ads can grow, especially among undecided voters, who are more likely to be influenced by the emotional content of the ads.
The sleeper effect also plays a significant role in advertising beyond politics. Consumers are bombarded with ads daily, whether watching television, browsing the internet, or scrolling through social media. Most people recognize ads for what they are—attempts to manipulate purchasing decisions. However, despite this awareness, ads still have an impact because of the sleeper effect. Over time, consumers may forget the advertiser’s motives but continue to internalize the message. A catchy slogan or an emotionally appealing ad can stick in the mind, influencing future purchasing decisions long after the source has been forgotten.
This phenomenon is particularly evident in the context of brand loyalty. Consumers may prefer a brand not because of any direct reasoned argument but because they have been exposed to consistent positive messaging. The source of the brand’s influence—the advertising campaign—becomes irrelevant over time, leaving only the brand’s identity and message to shape consumer behavior.
Why Advertising Still Works: The Power of the Sleeper Effect
Even though we may be aware of the persuasive intent behind advertising, it still works. Why? The sleeper effect provides a clear explanation for this paradox. Advertising works not because we are gullible but because our memories of the source fade, leaving behind only the message.
When we watch an ad, we often recognize it for what it is—an attempt to persuade us to buy a product or adopt a certain viewpoint. However, even the most discerning individuals are not immune to the sleeper effect. Over time, the memory of the ad’s source diminishes, leaving us with the message. The emotional appeal, the catchy jingle, or the striking imagery lingers in our minds, influencing our future behavior.
For example, a consumer might see an advertisement for a luxury car, and even though they know it’s an ad, they may still associate the car with status and success. Over time, the brand’s name may become associated with these positive attributes, even if the consumer forgets that the advertisement originally planted the idea. The message—that this car represents success and prestige—persists, while the fact that it was an ad fades into the background.
This is why advertising works even in the face of skepticism. The message sticks because of the sleeper effect, and as time passes, the ad’s persuasive power grows stronger, even if the consumer is aware of its intent. The challenge for marketers is not to convince consumers to buy immediately but to plant a seed that will grow over time, as the consumer forgets the source and internalizes the message.
How to Protect Yourself from the Sleeper Effect
While the sleeper effect is a powerful force, there are several strategies you can use to protect yourself from being unduly influenced by persuasive messages. The first step is to be mindful of unsolicited advice. Unsolicited advice often carries hidden motives, Whether from friends, family, or strangers. People may offer guidance because they stand to gain from influencing your behavior. You can protect yourself from being manipulated by questioning the source of any advice you receive.
The second strategy is to avoid sources that are heavily influenced by advertising. Many websites, news outlets, and media platforms are funded by advertisements, which can subtly shape the content they produce. While it’s nearly impossible to avoid ads entirely, you can be more selective about where you get your information. Books, for example, are generally free from the commercial influences that taint online content. By sticking to these ad-free sources, you can minimize your exposure to biased or manipulative messaging.
Finally, one of the most effective ways to guard against the sleeper effect is to actively question the source of the information you encounter. Whether you’re reading an article, watching a commercial, or listening to a speech, take the time to ask yourself: Who is behind this message? What are their motives? Why are they presenting this argument? By evaluating the source of every argument you encounter, you can avoid being swayed by persuasive messages that might otherwise take hold of your memory.
This process requires time and effort, but it will ultimately help you become a more discerning consumer of information. By constantly scrutinizing the source of the messages you encounter, you can reduce the likelihood of falling prey to the sleeper effect and make more informed, rational decisions.
Conclusion
The sleeper effect demonstrates the power of memory and the surprising endurance of persuasive messages. An argument’s influence can grow stronger through political propaganda, advertising, or the media, even when its source is discredited. Understanding how the sleeper effect works, we can better protect ourselves from its subtle power and make more informed, rational decisions. In a world where persuasive messages are ubiquitous, awareness of this phenomenon is crucial to maintaining autonomy over our beliefs and choices.
This article is part of The Art of Thinking Clearly Series based on Rolf Dobelli’s book.