Seeing double: levels of processing can cause false memory.

Ordinarily, deeper levels of processing in a study session increase the accuracy of later remembering. We modified the standard levels-of-processing procedure by presenting items either once or twice in the study phase, each item being the subject of a semantic, phonemic, or graphemic question. At test, the subjects judged the frequency with which each word had occurred in the study phase. Deeper processing during encoding increased accuracy in judging twice-presented items. However, it also caused an illusion of repetition for items presented only once. The result underlines the importance of thinking of remembering as a process of evaluation and inference, rather than simple retrieval.