Similarity and inhibition in long-term memory: Evidence for a two-factor theory

Recalling a past experience often requires the suppression of related memories that compete with the retrieval target, causing memory impairment known as retrieval-induced forgetting. Two experiments examined how retrieval-induced forgetting varies with the similarity of the competitor and the target i em (target-competitor similarity) and with the similarity between the competitors themselves (competitor-competitor similarity). According to the pattern-suppression model (M. C. Anderson & B. A. SpeUman, 1995), high target-competitor similarity should reduce impairment, whereas high competitor-competitor similarity should increase it. Both predictions were supported: Encoding target-competitor similarities not only eliminated retrieval-induced forgetting but also reversed it, whereas encoding competitor-competitor similarities increased impairment. The differing effects of target-competitor and competitor-competitor similarity may resolve conflicting results concerning the effects of similarity on inhibition. Bringing a memory to consciousness often involves the discrim-ination of the event we want from other similar memory traces. Retrieving the memory for where we parked today, for instance, may require that we overcome the repeated recollection of where we parked yesterday. Instances of retrieval interference such a