Rates of unconscious plagiarism were investigated using Brown and Murphy's 3-stage paradigm. Initially, participants completed the creative Alternate Uses Test (generation phase) and then at test, recalled their original ideas (recall-own phase) and generated new ideas (generate-new phase). In both of the testing phases, participants plagiarised by reporting someone else's ideas as either their own idea or a new idea. Plagiarism rates increased over a one week retention interval (Experiment 2) and both active and passive participants were equally likely to plagiarise someone else's idea as a new idea (Experiment 1). When an elaboration phase was incorporated into the paradigm, following idea generation, different types of elaboration had clear and consistent effects on participant performance. Elaboration by rating ideas positively and negatively improved correct recall (Experiment 3) and rating the imaginability of ideas (Imagery-elaboration IE) and improving the ideas in three ways (generative-elaboration GE) also increased correct recall to a comparable degree (Experiment 4). In the generate-new phase, these different types of elaboration either reduced plagiarism (Experiment 4) or did not affect the level of plagiarism relative to control (Experiment 3, 5, 6, 7 & 8). However, in the recall-own phase, the GE alone consistently led to the highest levels of unconscious plagiarism (relative to IE or control, Experiment 4, 5, 6, 8). This pattern prevailed when participants were encouraged not to plagiarise by means of a financial incentive (Experiment 5) or when their memory was assessed more stringently by a source monitoring task (Experiment 9). IE did not result in such recalled intrusions, even when it was matched in terms of content to the GE (Experiment 6) or when IE was repeated (3 days after generation) and thus strengthened (Experiment 7). Also, strengthening IE did not affect plagiarism levels in a source monitoring task (Experiment 11). Strengthening GE, on the other hand served to dramatically inflate the observable intrusions in both a recall-own task (Experiment 8) and in a source monitoring task (Experiment 10). Therefore, contrary to a strength account, the probability of plagiarising another's ideas as one's own is linked to the generative nature of the elaboration performed on that idea, rather than its familiarity. The theoretical and practical implications of these findings will be discussed.

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