What is the sleeper effect in simple terms?

You dismiss something at first because it came from an unreliable source, but over time you forget the source, remember the content, and gradually start to believe it.

Does the sleeper effect always occur?

No. It mainly appears when the message itself is persuasive, the information discrediting the source comes after the message, and people processed the content carefully. Reminding people of the source weakens it.

Sleeper Effect

🧠 Psychology By CampusDown Wiki Editorial Team Last updated October 27, 2026

The sleeper effect is the phenomenon in which a message from an untrustworthy source, or one flagged with a warning that it is false, barely changes attitudes at first but becomes more persuasive over time. It is explained by the message content staying in memory while its link to discounting cues, such as the source or the warning, weakens. Carl Hovland's research team first reported it while studying the effects of US Army propaganda films during World War II.

Contents

1. Discovery and the classic explanation
2. Debate and the dissociation hypothesis
3. Meta-analysis and misinformation research
4. FAQ
5. References

Discovery and the classic explanation

Hovland, Lumsdaine and Sheffield (1949) showed US soldiers the propaganda films Why We Fight and found that some opinion changes were larger nine weeks later than after five days. Hovland and Weiss (1951) presented the same articles under the names of high- and low-credibility sources. At first the high-credibility source was far more persuasive, but four weeks later the difference had nearly vanished. They explained this with the discounting cue hypothesis: over time people remember what was said better than who said it. Kelman and Hovland (1953) supported this account by showing that reminding people of the source later eliminated the sleeper effect.

Debate and the dissociation hypothesis

The sleeper effect later became controversial because it proved hard to replicate. Gillig and Greenwald (1974) failed to find it in seven experiments and asked whether it was time to lay the sleeper effect to rest. However, Gruder and colleagues (1978) and Cook and Flay (1978) identified conditions under which it reliably appears: the message is strong enough, the discounting cue comes after the message, and people process the content carefully. Pratkanis and colleagues (1988) proposed a differential decay hypothesis, in which a cue presented after the message is stored separately from the content in memory, so its influence fades faster. This ties into central route processing in the elaboration likelihood model (Petty and Cacioppo, 1986).

Meta-analysis and misinformation research

A meta-analysis of 72 experiments by Kumkale and Albarracín (2004) confirmed that the sleeper effect appears reliably when conditions are right. It is especially large when the message's arguments are strong, recipients are highly involved and able, and the discounting cue follows the message. The phenomenon matters today for misinformation research. Johnson and Seifert (1994) demonstrated the continued influence effect, in which corrected misinformation keeps shaping later inferences, and Lewandowsky and colleagues (2012) concluded that simple corrections or warnings that a source is untrustworthy are not enough to block misinformation's influence. Underwood and Pezdek (1998) reported a pattern resembling the sleeper effect in eyewitness memory, where misinformation from a low-credibility source grows more influential over time.

FAQ

What is the sleeper effect in simple terms?: You dismiss something at first because it came from an unreliable source, but over time you forget the source, remember the content, and gradually start to believe it.
Does the sleeper effect always occur?: No. It mainly appears when the message itself is persuasive, the information discrediting the source comes after the message, and people processed the content carefully. Reminding people of the source weakens it.

Sources reviewed: 2026-10-26

References

Hovland, C. I., Lumsdaine, A. A., & Sheffield, F. D. (1949). Experiments on Mass Communication. Princeton: Princeton University Press.
Hovland, C. I., & Weiss, W. (1951). The influence of source credibility on communication effectiveness. Public Opinion Quarterly, 15(4), 635–650.
Kelman, H. C., & Hovland, C. I. (1953). 'Reinstatement' of the communicator in delayed measurement of opinion change. Journal of Abnormal and Social Psychology, 48(3), 327–335.
Gillig, P. M., & Greenwald, A. G. (1974). Is it time to lay the sleeper effect to rest? Journal of Personality and Social Psychology, 29(1), 132–139.
Gruder, C. L., Cook, T. D., Hennigan, K. M., Flay, B. R., Alessis, C., & Halamaj, J. (1978). Empirical tests of the absolute sleeper effect predicted from the discounting cue hypothesis. Journal of Personality and Social Psychology, 36(10), 1061–1074.
Cook, T. D., & Flay, B. R. (1978). The persistence of experimentally induced attitude change. Advances in Experimental Social Psychology, 11, 1–57.
Petty, R. E., & Cacioppo, J. T. (1986). Communication and Persuasion: Central and Peripheral Routes to Attitude Change. New York: Springer.
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, 54(2), 203–218.
Johnson, H. M., & Seifert, C. M. (1994). Sources of the continued influence effect: When misinformation in memory affects later inferences. Journal of Experimental Psychology: Learning, Memory, and Cognition, 20(6), 1420–1436.
Underwood, J., & Pezdek, K. (1998). Memory suggestibility as an example of the sleeper effect. Psychonomic Bulletin & Review, 5(3), 449–453.
Kumkale, G. T., & Albarracín, D. (2004). The sleeper effect in persuasion: A meta-analytic review. Psychological Bulletin, 130(1), 143–172.
Lewandowsky, S., Ecker, U. K. H., Seifert, C. M., Schwarz, N., & Cook, J. (2012). Misinformation and its correction: Continued influence and successful debiasing. Psychological Science in the Public Interest, 13(3), 106–131.

Reports and materials that use this theory (Korean)

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Elaboration Likelihood ModelThe Elaboration Likelihood Model explained: Petty and Cacioppo's (1986) theory of persuasion with a central route of careful argument processing and a peripheral route of cues such as attractiveness or expertise. Covers motivation, ability and advertising.🧠 Psychology Misinformation and Confirmation BiasWhy false information spreads and why people accept it. Covers mis-, dis- and mal-information, confirmation bias from Wason's task onward, filter bubbles and echo chambers, the continued influence effect, and remedies such as fact-checking and prebunking.🎨 Media, Arts & Culture Cognitive Dissonance TheoryFestinger's cognitive dissonance theory explained: definition, dissonance reduction, the $1/$20 experiment, effort justification, free choice, criticisms, and report examples.🧠 Psychology Cialdini's principles of persuasionRobert Cialdini's six principles of influence from his 1984 book Influence—reciprocity, commitment and consistency, social proof, liking, authority, and scarcity—plus the seventh principle, unity (2016), the research behind them, and how to resist them.🧠 Psychology Streisand EffectWhat the Streisand effect is: attempts to hide or remove information end up spreading it far wider. Covers its origin, reactance theory and censorship backfire, empirical studies of online censorship in China and Saudi Arabia, and when it fails to occur.👥 Sociology

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This article was last updated on October 27, 2026. It is based on widely recognized original works and textbooks; when citing it in a paper, please check the original sources listed in the references.