The Sleeper Effect

· March 10, 2019
The sleeper effect is a psychological phenomenon that states that you believe information from an unreliable source sometime after you've heard it.

The sleeper effect is a term that refers to the influence that a piece of information that you initially discarded as false has on you. According to some theories, this effect involves someone initially ignoring a message that doesn’t seem to be credible. However, they eventually come to believe the information they believed to be false. This change can come about due to new external evidence that supports the claim. On the other hand, it can come from internal musings that push you to re-evaluate the information.

This strategy can seem a little contradictory because you tend to question messages that you initially don’t believe more than those you do. Nevertheless, this doesn’t mean that some pieces of information that are stored in your memory won’t someday be important, even if you initially believed them to be dubious. They start to become significant when you find other data that makes you change your mind.

A cloud on a blackboard representing a woman's thoughts.

The origins of the sleeper effect

In the 1940s, during World War II, governments rolled out many advertising campaigns to make people see the war in a positive light. Specifically, the United States Department of War wanted to know whether or not their propaganda films were being effective.

With this goal in mind, they developed a series of experiments to analyze how the films affected soldiers’ attitudes. The results were quite strange. The researchers discovered that the short films didn’t impact the attitudes of the soldiers as they had expected.

When the movies were of an informative nature, they strengthened some already existing attitudes. However, they generally didn’t make the soldiers more optimistic. The producers and psychologists hadn’t achieved the goal they’d created the short films for in the first place.

Oddly, what they discovered was that, after a few months, these short films exerted a curious effect on the soldiers. While they didn’t change their attitudes toward the war immediately, nine months after, the researchers noted some changes. For example, those soldiers who saw the film The Battle of Britain demonstrated slightly higher sympathy for the British. Nine weeks later, this level of sympathy increased. Carl Hovland, a professor at Yale University, called this phenomenon “the sleeper effect.”

As you would expect, this phenomenon has been broadly debated in scientific psychology because it’s hard to say precisely whether the changes in attitudes, after such a long period of time, should be attributed solely to the viewing of a short film.

Some reliable studies show that the persuasive effect of a message is at its highest right after you get the information. Accordingly, you would assume that the more time passes, the more the influence decreases. Advertisers know this. That’s why they often offer some reward to those who make purchases quickly.

Required conditions

In order for this phenomenon to manifest, two essential conditions are required:

  • A strong initial impact: the sleeper effect only emerges if the persuasive message has a strong initial impact. This is because a strong impression guarantees it’ll stay in memory and thoughts for longer.
  • A message we see as common sense: when the source of the information isn’t reliable, you tend to discredit the message. Nevertheless, if you find that the source isn’t credible only after having seen the movie, then you’ll be more receptive to the messages and also more suggestible.

Advertisers know this fact very well. For example, they can post an article on the benefits of chocolate to convince people to eat more of it. At the end of the article, they reveal that the writer’s affiliated with a company that manufactures chocolate. So when you get a persuasive message before knowing its source, you’ll be more liable to experience the sleeper effect.

The sleeper effect may come as a result of inconsistencies in your memory.

The explanation for this phenomenon might be very simple. Some say that your mind, as time goes on, forgets that the source of the information wasn’t totally trustworthy. Even so, the information itself remains. This is the reason why you become more susceptible to believing data from unreliable sources later on as opposed to when you first read it.

The sleeper effect is one of the ways in which advertisements and the media can persuade you to pay attention to something. It can also make you buy things or vote for a specific candidate. Additionally, this phenomenon can make you ignore the bad parts of the product they’re offering.

Tarcan Kumkale, G., & Albarracín, D. (2004). The Sleeper Effect in Persuasion: A Meta-Analytic Review. Psychological Bulletin.

Pratkanis, A. R., Greenwald, A. G., Leippe, M. R., & Baumgardner, M. H. (1988). In Search of Reliable Persuasion Effects: III. The Sleeper Effect is Dead. Long Live the Sleeper Effect. Journal of Personality and Social Psychology.

Lariscy, R. A. W., & Tinkham, S. F. (1999). The sleeper effect and negative political advertising. Journal of Advertising.

Albarracín, D., Kumkale, G. T., & Vento, P. P. Del. (2017). How people can become persuaded by weak messages presented by credible communicators: Not all sleeper effects are created equal. Journal of Experimental Social Psychology.