Underwood, J. & Pezdek, K. (1998). Memory suggestibility as an example of the sleeper effect. Psychonomic Bulletin & Review, 5, 449-453.
- This study investigates the suggestibility of memory and the effects of source credibility and time delay.
- High-credibility communicators are rated as more effective than low-credibility communicators even when presentations are identical. After a four-week delay, both communicators were rated similarly. Thus, source credibility was no longer significant due to the sleeper effect.
- Availability-valence hypothesis -- A particular message is encoded along with the source credibility. If this information is quickly recalled, the individual will associate the source with the message. After some time, the more memorable message can be recalled, but the less memorable source is forgotten. Therefore, the message may be cited with confidence (because of high availability and weaker association) even if the source had low-credibility.
- When subjects receive misleading information, the probability that they will later falsely recognize the information as true increases, especially when the source is highly credible.
- Lampinen and Smith found that when children received misleading information from a credible source, they were more likely to be suggestively influenced than children who received misleading information from a low-credibility source.
- Hypothesis: The number of falsely recognized misleading items shoulc be greater for misled subjects than the control group. This effect should be especially strong for misled subjects in the delay condition.
- The design was 2(source credibility) X 2(time) X 2(misled vs. control condition) with the first two factors varied between subjects. There were four groups: high-credibility immediate test, high-credibility delay test, low-credibility immediate test, and low-credibility delay test.
- Presentation phase: Two slide sequences were presented. Each sequence contained 2 target slides out of 26.
- Suggestion phase: Two postevent narratives were read back to back, and subjects were told to visualize the slides while reading. Each of the two narratives had a correct description of one target slide and a misleading description of the other target slide.
· Low-credibility condition: A four-year-old boy was credited for the narrative.
· High-credibility condition: A memory psychologist was credited for the narrative.
- Recognition memory test phase: Subjects in the immediate condition completed the recognition memory task, and subjects in the delay condition completed it one month later.
· The test had 12 yes or no questions -- 3 for each target slide.
- Subjects in the low-credibility condition falsely recognized more misled items after the delay than those who were tested immediately. The rate at which these items were recognized was similar to the rate at which subjects recognized items described by a highly credible source. (See Figure 1)
- The hypothesis was confirmed that misleading information and its source will become disassociated as time passes, therefore increasing the chance that a subject will be suggestively misled, especially by a low-credibility source.
- The cognitive processes underlying the sleeper affect appear to be similar to those underlying memory suggestibility.
- Source-monitoring interpretation: It is possible that when subjects heard both narratives they confused which source described them. Therefore, there would be less association between source credibility and the information during encoding.
- The study suggests that initially, people can discriminate between a low- and high-credibility source and are less likely to be misled by a low-credibility source. After the passage of time, the ability to discriminate diminishes leading to the formation of false memories.
· This finding can be applied to jury decision making, deceptive tabloid stories, and misinterpreted scientific data analysis.