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The Sleeper Effect

One of the phenomena discovered by Hovland and colleagues was called the sleeper effect. It is based on the insight that source credibility effects are temporary. After some time passes, the message is remembered but the source may be forgotten, so any effect from source degradation or similar tactics is lost. Kelman and Hovland (1953) found that initially high-credibility sources were more persuasive than low-credibility sources, but after a few weeks the difference disappeared. Then messages from a low-credibility source were rated as equally persuasive.

What is the "sleeper effect"?

Hovland and Weiss documented the sleeper effect in a study where people read an essay about the effectiveness of atomic submarines. Some of the subjects were told the essay came from an untrustworthy source. (The Soviet newspaper Pravda was chosen for this role, reflecting the cold war atmosphere of the 1950s.) Other subjects were told the information came from Fortune magazine, a source that students of the 1950s regarded as fairly reliable, but not a place they would expect to find expert information about nuclear submarines. Still other subjects were told the information came from a Nobel Prize-winning nuclear physicist, a highly credible source of information on this issue.

How did Hovland and Weiss document the sleeper effect, using information about nuclear submarines?

Source credibility made a big difference at first. However, after a month had passed, two things happened. First, the difference in attitudes between the groups disappeared. Now the Pravda group had as much admiration for the ideas expressed in the article as the nuclear physicist group. Second, people could no longer name the source. This was called the sleeper effect because it implied that propaganda from an unreliable source might be ineffective at first, but it would sleep in the background, and eventually—after the memory for the source was gone—the information from an unreliable source might be just as persuasive as information from an expert source.

How did Pratkanis and colleagues demonstrate the cause of the sleeper effect?

In a series of 17 studies, Pratkanis and colleagues (1988) produced data that documented and explained the sleeper effect. They found that memory for the "discounting cue" (information that the messenger was unreliable) disappeared more quickly than memory for the message. Naturally, when the negative information about the source was forgotten, but the message itself was remembered, the message gained more credibility.

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