The sleeper effect is a psychological phenomenon that relates to persuasion. It is a delayed increase in the effect of a message that is accompanied by a discounting cue. A discounting cue being some negative connotation or lack of credibility in the message. Where a positive message may evoke an immediate positive response which decays over time, the sleeper effect refers to a delayed positive response that is maintained over time. The effect was first noticed among US Army soldiers exposed to army propaganda. It was hypothesized that over time the soldiers forgot that the message was propaganda. The effect has been widely studied but notoriously difficult to reproduce, leading to some doubt over its existence. The sleeper effect When people are exposed normally to a persuasive message (such as an engaging or persuasive television advertisement), their attitudes toward the advocacy of the message display a significant increase. Over time, however, their newly formed attitudes seem to gravitate back toward the opinion held prior to receiving the message, almost as if they were never exposed to the communication. This pattern of normal decay in attitudes has been documented as the most frequently observed longitudinal pattern of persuasion research (Eagly & Chaiken, 1993). In contrast, some messages are often accompanied with a discounting cue (e.g., a message disclaimer, a low-credibility source) that would arouse a recipient’s suspicion of the validity of the message and suppress any attitude change that might occur by exposure to the message alone. Furthermore, when people are exposed to a persuasive message followed by a discounting 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 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 persuaded initially. However, even though the source of the advertisement lacked credibility, voters will be more likely to be persuaded later (and ultimately, vote against the candidate disfavored by 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