The effectiveness of persuasion is very much dependent on the source of the information. Sources with high credibility are more persuasive than low-credibility sources (Pornpitakpan, 2004). In order for us to count a source as credible, they must be seen as being competent or having expertise, and they must be trustworthy (Hass, 1981). Therefore, the way that we interpret information is very much affected by the source that we are getting the information from.

Although the sources of our information very much affect how we interpret the information, the actual information itself is more important than the source. According to Pratkanis et al. (1988) we remember messages but we forget the source that they came from. This causes the sleeper effect to occur. The sleeper effect refers to the delayed impact of persuasion from sources that we find to be non-credible. So, in the long run, messages stay prominent in our minds but sources fade away. Recent research has shown that the sleeper effect is reliable as long as people receive information before learning who the source is (Kumkale & Albarracin, 2004). So, if someone hears a message and then hears the source, then the message will tend to remain while the source that it came from will fade. However, if the source is learned first, it will be immediately judged as credible or non-credible, and the information will be interpreted based on that judgment.

I can remember times in high school when I experienced the sleeper effect. My mom had a friend that liked to gossip a lot about things that were going on at my high school. For the purposes of the story, let's call her Lisa. I had a bit of a problem with Lisa and I definitely counted her as a non-credible source of information. I would often hear things from Lisa or my mom would tell me things that she said, and I would usually count them as being non-credible and dismiss the information. However, I can remember many times when I would find myself remembering information that I had heard from somewhere, but not being able to figure out where it came from and having a hard time deciding whether it was good information or not.

Looking back on it now, I think that I was probably experiencing the sleeper effect. I counted my mom as a credible source, but I did not count Lisa as a credible source. I know that my mom would often mention things to me in different ways. Sometimes she would say things like, "Lisa told me..." and then give me some information that I would dismiss because I knew it was coming from Lisa. Other times, though, my mom would just tell me things, and then I would ask her where the information came from after she had already told me. This is why I think I had a hard time figuring out where I got different bits of information from. Those bit of information presented before hearing who the source was would stay prominent in my memory while the source would fade.

Eventually, I began to just tell my mom that I didn't want to hear anything if it was coming from Lisa's mouth. For this reason, actually, I began to hate gossip more than anything. I actually begged my mom to stop being friends with Lisa. It is interesting, though, to look back and realize how, even though I dismissed Lisa as a source, the information that came from her still managed to persevere in my mind sometimes.

References
Hass, R. G. (1981). Effects of source characteristics on the cognitive processing of persuasive messages and attitude change. In R. Petty, T. Ostrom, & T. Brock (Eds.), Cognitive responses in persuasion (pp. 141-171). Hillsdale, NJ: Erlbaum.

Kumkale, G. T., & Albarracin, D. (2004). The sleeper effect in persuasion: A meta-analytic review. Psychological Bulletin, 130, (143-172).

Pornpitakpan, C. (2004). The persuasiveness of source credibility: A critical review of five decades' evidence. Journal of Applied Social Psychology, 34, 243-281

Pratkanis, A. R., Greenwald, A. G., Leippe, M. R., & Baumgardner, M. H. (1988). In search of reliable persuasion effects: III. The sleeper effect is dead. Long live the sleeper effect. Journal of Personality and Social Psychology, 54, 203-218.