The Influence of Pre-existing Memories on Retrieval-Induced Forgetting

When people form episodic connections between memories that share a common retrieval cue, the tendency for those memories to interfere in later retrieval is often eliminated, and forgetting of the interfering information is reduced. For example, episodic integration protects memories from retrieval-induced forgetting (RIF), a phenomenon in which practicing retrieving some associates of a cue leads to the suppression of others that interfere with retrieval (Anderson, Green, & McCulloch, 2000). The purpose of this study was to determine whether semantic integration, as a result of pre-existing associations between practiced items and their unpracticed competitors, also moderates RIF. This research was motivated by the existence of many pre-existing associations between the practiced and unpracticed sets in one study that failed to replicate the RIF effect with item specific cues (Butler, William, Zacks, & Maki, 2001). It was hypothesized that pre-existing associations increase the implicit, semantic integration among the items, “insulating” them from inhibitory effects. The results were consistent with this hypothesis: when associations between the practiced and nonpracticed sets were maximized, no forgetting was observed, however when such associations were minimized, there were reliable levels of RIF. The benefits of semantic integration were replicated across four experiments including one that used Butler’s original materials and design. Furthermore, when Butler’s items were simply re-arranged in order to minimize the associations and thus reduce semantic integration, the typical RIF effect was observed. Additional results revealed that the moderating effects of semantic integration are not mediated by explicit integration strategies. Participants who received incidental learning instructions and so reported very low levels of episodic integration, still exhibited the same benefits of semantic integration. Finally, it was also shown that increasing the use of explicit integration strategies by increasing the study time, also reduced the RIF effect. The results of the current set of studies reveal that failure to control for pre-existing associations may account for variability in the RIF phenomenon. The results also suggest that the memory system is adaptive to the needs of the organism, in that it operates to keep related memories that are necessary for cognition active, but suppresses interfering memories