False memories are more likely to be planted for plausible than for implausible events, but does just knowing about an implausible event make individuals more likely to think that the event happened to them? Two experiments assessed the independent contributions of plausibility and background knowledge to planting false beliefs. In Experiment 1, subjects rated 20 childhood events as to the likelihood of each event having happened to them. The list included the implausible target event "received an enema," a critical target event of Pezdek, Finger, and Hodge (1997). Two weeks later, subjects were presented with (1) information regarding the high prevalence rate of enemas; (2) background information on how to administer an enema; (3) neither type of information; or (4) both. Immediately or 2 weeks later, they rated the 20 childhood events again. Only plausibility significantly increased occurrence ratings. In Experiment 2, the target event was changed from "barium enema administered in a hospital" to "home enema for constipation"; significant effects of both plausibility and background knowledge resulted. The results suggest that providing background knowledge can increase beliefs about personal events, but that its impact is limited by the extent of the individual's familiarity with the context of the suggested target event.

Numerous studies have increased people's confidence in the occurrence of various childhood events, however, Pezdek, Finger, and Hodge (1997) were able to successfully increase participants' confidence in one event (e.g., being lost in a mall), but not another (e.g., having received an enema). Two experiments considered two factors, plausibility and schematicity, as explanations for this differential suggestibility. In Experiment 1, participants completed a questionnaire regarding the likelihood of experiencing various childhood events, including receiving an enema. Two weeks later, they were given schematic or plausibility information about enemas, or both, or neither. Finally, participants again completed the previous questionnaire regarding childhood experiences. Only plausibility increased participants' beliefs that they had experienced an enema during childhood. In Experiment 2, participants were additionally asked about whether they had a memory of the event. While participants still responded with greater confidence that they had experienced an enema when given plausibility information, it did not increase their memory for the event, and schematicity actually decreased reported memory for the experience. The potential implications of these findings for the formation of false memories of sexual abuse are considered.

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