Journal of Experimental Psychology: Learning, Memory, and Cognition 1994, Vol. 20, No. 5,1063-1087 Copyright 1994 by the American Psychological Association, Inc. 0278-7393/94/13.00 Remembering Can Cause Forgetting: Retrieval Dynamics in Long-Term Memory Michael C. Anderson, Robert A. Bjork, and Elizabeth L. Bjork Three studies show that the retrieval process itself causes long-lasting forgetting. Ss studied 8 categories (e.g., Fruit). Half the members of half the categories were then repeatedly practiced through retrieval tests (e.g., Fruit Or ). Category-cued recall of unpracticed members of practiced categories was impaired on a delayed test. Experiments 2 and 3 identified 2 significant features of this retrieval-induced forgetting: The impairment remains when output interference is controlled, suggesting a retrieval-based suppression that endures for 20 min or more, and the impairment appears restricted to high-frequency members. Low-frequency members show little impairment, even in the presence of strong, practiced competitors that might be expected to block access to those items. These findings suggest a critical role for suppression in models of retrieval inhibition and implicate the retrieval process itself in everyday forgetting. A striking implication of current memory theory is that the very act of remembering may cause forgetting. It is not that the remembered item itself becomes more susceptible to forget- ting; in fact, recalling an item increases the likelihood that it will be recallable again at a later time. Rather, it is other items—items that are associated to the same cue or cues guiding retrieval—that may be put in greater jeopardy of being forgotten. Impaired recall of such related items may arise if access to them is blocked by the newly acquired strength of their successfully retrieved competitors (Blaxton & Neely, 1983; Brown, 1981; Brown, Whiteman, Cattoi, & Bradley, 1985; Roediger, 1974, 1978; Roediger & Schmidt, 1980; Run- dus, 1973). This implication follows from three assumptions underlying what we herein refer to as strength-dependent competition models of interference: (a) the competition assumption—that memories associated to a common cue compete for access to conscious recall when that cue is presented; (b) the strength- dependence assumption—that the cued recall of an item will decrease as a function of increases in the strengths of its Michael C. Anderson, Robert A. Bjork, and Elizabeth L. Bjork, Department of Psychology, University of California, Los Angeles. The research reported herein was supported in part by Grant 4-564040-RB-19900 to Robert A. Bjork and Grant 4-564040-EB-19900 to Elizabeth L. Bjork from the Committee on Research, University of California, Los Angeles, and by Grant MDA 903-89-K-0179 to Keith Holyoak from the Army Research Institute. The article appears on University Microfilms as part of a dissertation submitted to the University of California, Los Angeles, in fulfillment of the degree of PhD for Michael C. Anderson. We gratefully acknowledge the assistance of Myra Jimenez, Steven Machado, and Shirley Yu in the collection of data and of Catherine Fritz, Dina Ghodsian, Keith Holyoak, Keith Horton, John Shaw, Bobbie Spellman, and Tom Wickens for comments on drafts of this article. We also thank Todd Gross, Steven Machado, Anthony Wag- ner, and especially Bobbie Spellman for many thoughtful conversa- tions on the topic of retrieval inhibition. Correspondence concerning this article should be addressed to Michael C. Anderson, Department of Psychology, University of California, 405 Hilgard Avenue, Los Angeles, California 90024-1563. competitors' associations to the cue; and (c) the retrieval-based learning assumption—that the act of retrieval is a learning event in the sense that it enhances subsequent recall of the retrieved item. Taken together, these assumptions imply that repeated retrieval of a given item will strengthen that item, causing loss of retrieval access to other related items. We refer to this possibility as retrieval-induced forgetting. In this article, we explore two questions regarding retrieval-induced forget- ting, one empirical and the other theoretical: (a) Is retrieval- induced forgetting a significant factor producing fluctuations in the long-term accessibility of knowledge? and (b) To what extent do such effects support the strength-dependence assump- tion? We believe that exploring these questions may help solve the puzzle of why so little of the knowledge available in long-term memory remains consistently accessible. Many studies illustrate that prior retrievals can make subse- quent retrieval of related information more difficult, at least within the context of a single testing session. For example, in the domain of episodic memory, the study of output interfer- ence has shown that an item's recall probability declines linearly as a function of its serial position in a testing sequence. This decline has been demonstrated with recall of paired associates (Arbuckle, 1966; Roediger & Schmidt, 1980; Tulv- ing & Arbuckle, 1963,1966) and categorized word lists (Dong, 1972; Roediger, 1973; Roediger & Schmidt, 1980; Smith, 1971, 1973; Smith, D'Agostino, & Reid, 1970); it occurs regardless of a category's serial position in the learning list (Smith, 1973), and it does not result from the loss of items from primary memory over time (Smith, 1971). In semantic memory, speeded generation of several category exemplars on the basis of letter cues (e.g., Fruit A ) slows generation of later exemplars and increases the number of generation failures (Blaxton & Neely, 1983; Brown, 1981; Brown et al., 1985). These effects of output interference in both episodic and semantic memory violate expectations derived on the basis of semantic priming and spreading activation, according to which retrieval should facilitate recall of related knowledge, not impair it (Loftus, 1973; Loftus & Loftus, 1974; Neely, 1976; Warren, 1977). These effects show that retrieval-induced forgetting does occur, at least within a single testing session, which some 1063