In social psychology, this is used to describe the impact of a persuasive message. Generally, the power of a persuasive message will tend to fade over time. With the sleeper effect, a message from a low-authority source can gain momentum and increase in persuasiveness over time if the conditions are conducive.
Low authority may be due to a discounting cue like a prediction for sunny skies given by the TV weatherman (who is presumed to be biased and a people pleaser). However, if the message is disseminated from another source (by dissociation), it gains more credibility. While this sounds incredulous, it does work or at least the impact shows a significant slowing down.
How it works
The sleeper effect might sound like those psychological theories that defy sense or explanation. Naturally, the persuasion factor of a message should be at its best just after it is delivered. With time, the effect should fade and people should return to their original attitudes – while true for most cases, it has been proved otherwise by Kumkale & Albarracin, 2004.
However, there are specific conditions that should hold true for the sleeper effect to come into force:
Massive first impact
The first impact of the message would have to be immense for it to invoke the sleeper effect. If that does not occur, the message will simply filter right through in a while.
The source of the message should be obvious in its lack of credibility so that it can be easily disbelieved.
What is actually at work is that people are persuaded by the arguments presented until they realize that the source cannot be discredited. But as the discounting cue tends to fall through in most people, they tend to forget that they had discounted the message after some time. By now, the contents of the message have been completely digested by the recipient and it accomplishes its mission.
This is why persistence in sending a sales message will end in positive results over a period of time.