Sleeper effect

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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, typically being some negative connotation or lack of credibility in the message, while a positive message may evoke an immediate positive response which decays over time. The sleeper effect also 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.