of the source in the movie, participants later reported a slight increase of persuasion (much to the researchers’ surprise). After examining the results, they initially hypothesized that forgetting of the discounting cue (in this case, the non-credible source) was causing the effect. Over time, however, the effect of the messages presented by credible sources decayed, whereas the effect of the messages presented by non-credible sources either remained the same or increased slightly. Despite evidence for the sleeper effect from this series of studies, the recall measures indicated that recipients could still remember the non-credible sources of the messages at the time of the delayed follow-up. This is when the forgetting hypothesis was replaced by the dissociation hypothesis. Now according to the dissociation hypothesis the sleeper effect does not need to imply that the discounting cue becomes permanently unavailable in memory. A weakened association between the cue and the message may be sufficient for the sleeper effect to occur. As the association weakens over time, rendering the cue less accessible in relation to the communication topic, there may be a delayed increase in persuasion as long as the message arguments are still memorable. To this extent, factors that facilitate retention of the message content should create settings conducive to the sleeper effect. According to this reasoning, the sleeper effect occurs because the association between the discounting cue and the message in one’s memory becomes weakened over time; hence, when the message is recalled for purposes of producing an attitude, the source is not readily associated. Differential decay Something that Hovland and his team ignored that is important is why over time, the discounting cue becomes less accessible than the message even when both pieces are similarly effective at the onset. To answer this question Greenwald, Pratkanis, and their team (Greenwald et al., 1986; Pratkanis et al., 1988) implemented a study to identify the conditions by which the sleeper effect does and does not occur. Pratkanis directed a series of seventeen experiments in which he presented the discounting cue either before or after the message and found that the sleeper effect occurred mostly when the cue followed the message but not when the cue was first. In order to explain his findings, Pratkanis and his team proposed a modified forgetting hypothesis, which suggested that the sleeper effect occurs because the effect of the message and the cues decay at different rates. Based