When people are normally exposed to a highly persuasive message (such as an engaging or persuasive television ad), their attitudes toward the advocacy of the message display a striking increase. Over time, however, their newly formed attitudes seem to gravitate back toward the position held prior to receiving the message, almost as if they were never exposed to the communication in the first place. This pattern of normal decay in attitudes has been documented as the most frequently observed longitudinal pattern in persuasion research (Eagly & Chaiken, 1993). In contrast, some messages are often accompanied with a discounting cue (e.g., a message disclaimer, or perhaps the message was delivered by a low-credibility source) that would arouse a recipient’s suspicion of the validity of the message, and ultimately suppress any attitude change that might occur with exposure to the message alone. Furthermore, when people are exposed to a persuasive message followed by such a cue, people tend to be more persuaded over time; this is referred to as the sleeper effect (Hovland & Weiss, 1951; Cook & Flay, 1978). For example, in political campaigns during important elections, undecided voters often see negative advertisements about a party or candidate running for office. At the end of the advertisement, they also might notice that the opposing candidate paid for the advertisement. Presumably, this would make voters question the truthfulness of the advertisement, and consequently, they may not be initially persuaded. However, even though the source of the advertisement lacked credibility, voters will still be more likely to be persuaded later, and ultimately, vote against the candidate in the advertisement. This pattern of attitude change has puzzled social psychologists for nearly half a century, primarily due to its counter-intuitive nature and for its potential to aid in understanding attitude processes (Eagly & Chaiken, 1993). In addition, it has been the most widely studied phenomenon in persuasion research (Kumkale & Albarracín, 2004; see also Cook & Flay, 1978).
One of the more challenging aspects that the sleeper effect posed to some researchers in early studies was the mere difficulty in obtaining the effect (e.g. Capon & Hulbert, 1973; Gillig & Greenwald, 1974). After attempting to replicate the effect and failing, some researchers went as far as suggesting that it might be better to accept the null hypothesis and conclude that the sleeper effect does not exist (Gillig & Greenwald, 1974). However, Cook and his associates (Cook, Gruder, Hennigan, & Flay, 1979) responded by suggesting that previous studies failed to obtain the sleeper effect because the requirements for a strong test were not met. Specifically, they argued that the sleeper effect will occur only if: (a) the message is persuasive, (b) the discounting cue has a strong enough impact to suppress initial attitude change, (c) enough time has passed between immediate and delayed post-tests, and (d) the message itself still has an impact on attitudes during the delayed post-test. Experimental studies conducted did, in fact, provide support for the sleeper effect occurring under such theoretically relevant conditions (Gruder, Cook, Hennigan, Flay, Alessis, & Halamaj, 1978). Furthermore, the sleeper effect did not occur when any of the four requirements were not met.
Because the sleeper effect has been considered to be counter-intuitive at face value, researchers since the early 1950s have attempted to explain how and why it occurs.
This relatively complicated literature has been synthesized recently in a meta-analysis (see Kumkale & Albarracin, 2004).
Capon, N., & Hubert, J. The sleeper effect - an awakening. Public Opinion Quarterly, 37, 333-358.
Cook, T. D., Gruder, C. L., Hennigan, K. M., & Flay, B. R. (1979). History of the sleeper effect: Some logical pitfalls in accepting the null hypothesis. Psychological Bulletin, 86, 662-679.
Cook, T. D. & Flay, B. R. (1978). The persistence of experimentally-induced attitude change. In L. Berkowitz (Ed.), Advances in experimental social psychology (pp.1-57). New York: Academic Press.
Eagly, A. K., & Chaiken, S. (1993). The psychology of attitudes. Fort Worth, TX: Harcourt Brace Jovanovich.
Gillig, P. M., & Greenwald, A. G. (1974). Is it time to lay the sleeper effect to rest? Journal of Personality and Social Psychology, 29, 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, 1061-1074.
Hovland, C. I., Lumsdaine, A. A., & Sheffield, F. D. (1949). Experiments on mass communication. Princeton, NJ: Princeton University Press.
Hovland, C. I., & Weiss, W. (1951). The influence of source credibility on communication effectiveness. Public Opinion Quarterly, 15, 635-650.
Kumkale, G. T., & Albarracín, D. (2004). The sleeper effect in persuasion: A meta-analytic review. Psychological Bulletin, 130, 143-172.
Pratkanis, A. R., Greenwald, A. G., Leippe, M. R., & Baumgardner, M. H. (1988). In search of reliable effects: III. The sleeper effect is dead. Long live the sleeper effect. Journal of Personality and Social Psychology, 54, 203-218.