Sleeper effect

A sleeper effect of a message can be defined as a delayed increase in the effect size of that message. The sleeper metaphor entails its concern with the awakening of persuasive power after a period of sleep. A sleeper effect of messages from low-credibility sources was established in the pioneering work of Carl Hovland and colleagues. Such an unconditioned effect was not found in follow-up research. A 2004 meta-study limited the sleeper effect to cases in which a highly credible message was discounted, either by its attribution to a low-credibility source or by message disclaimers. The explanation of the sleeper effect is the fast decay of message sources in memory compared to the slower decay of message memory. Scholars who investigated the strong persuasive power of exemplars hypothesized that the slow decay of exemplars would explain the sleeper effect. Other research on sleeper effects does not rely on memory decay, but on delayed events that trigger the awakening of the persuasive power of old messages. Negative news may immediately lead to distrust in incumbent political leaders, while party loyalty remains unaffected until a shocking event, such as the murder of an opposition leader, triggers the awakening of the impact of distrust on party choice (i.e., a loss for the incumbent parties). In the age of digital media, many different types of sleeper effects are to be expected. Investigating them and incorporating them into a single theory of sleeper effects is a major intellectual challenge.