Retrieval-Induced Forgetting in a Multiple-Trace Memory Model

Retrieval-Induced Forgetting in a Multiple-Trace Memory Model Collin Green (cgreen@arc.nasa.gov) Human Factors Research & Technology, NASA Ames Research Center, Moffett Field, CA 94035 Aniket Kittur (nkittur@ucla.edu) Department of Psychology, University of California, Los Angeles, CA 90095 ticed items in practiced categories (target items), unprac- ticed items in practiced categories (competitor items), and unpracticed items in unpracticed categories (unpracticed items). After a delay, there was a category-cued recall test for all items. Results indicated that target items were recalled better than unpracticed items. Competitor items were recalled less often than unpracticed items. The latter result is surprising given that competitors were categorically related to targets; a spreading activation model would have predicted better recall for competitors than for unpracticed items. Anderson, Bjork, and Bjork (1994) explained this result in terms of an inhibitory mechanism. They postulated that during retrieval practice, competitors became active and competed with tar- gets for retrieval. To facilitate retrieval of targets, competi- tors were inhibited, and inhibition had a lasting negative impact on the availability of competitors. This effect is called Retrieval-Induced Forgetting (RIF). Abstract Behavioral studies (e.g., Anderson, Bjork, & Bjork, 1994) suggest that competition between relevant and irrelevant memory information is resolved in part through the inhibition of competing irrelevant information, an effect dubbed Re- trieval-Induced Forgetting (RIF). Green and Kittur (2004) outlined MNEM, a model of human memory that exhibits many retrieval dynamics observed in empirical studies (e.g., spacing and practice effects, forgetting over time, spontane- ous recovery, serial position effects), but did not account for RIF. In this paper, we describe a modified version of MNEM that incorporates an inhibitory mechanism and simulates some basic RIF effects. Prior work that implicates a feature-specific inhibitory mechanism provides a context for the model and simulations. Keywords: memory, modeling, similarity, retrieval, inhibi- tion, forgetting Introduction Similarity and the Pattern Suppression Model This article describes a computational memory model that incorporates an inhibitory mechanism. We begin by describ- ing retrieval-induced forgetting (RIF) and discussing one proposed form of an inhibitory mechanism (feature-based inhibition) that is suggested by behavioral data. We then describe our model, simulation results consistent with em- pirical findings, and our ongoing work on this project. Retrieval-Induced Forgetting Anderson and Spellman (1995) posited that RIF effects might rely on inhibition of one of two types: the associative link between a category cue and an exemplar might be weakened or the exemplar representation itself could be weakened. To choose between these hypotheses they used new, unstudied cues (called independent probes) during the test phase of RIF experiments to probe memory for studied items. For example, when Fruit-Apple was a competitor item, later recall of Apple could be tested with an independ- ent probe (Red-Ap_____). RIF effects were observed even when independent probes were used to test memory for studied items, ruling out inhibition of the associative link as an explanation. Anderson and Spellman (1995) concluded that inhibition acted directly on the representations of competitor items. They suggested that the inhibitory mechanism underlying RIF might act on individual features (sub-symbolic ele- ments) of memory representations and proposed the pattern suppression model (PSM) in which the featural representa- tion of a memory item is suppressed. The PSM postulates that features that are activated during retrieval but that are not components of the target are inhibited. Because com- petitor items are activated during retrieval many of their features are subject to inhibition, leading to RIF effects. The PSM also predicts that the featural overlap (similarity) of targets and competitors should affect the magnitude of RIF (see Figure 1). In Figure 1a, the competitor Banana has many features Many details of an average day are only subtly different than details of the day before. For instance, you may park your car in the same lot every day. The location of your car within that lot probably varies from day to day. With many memories linked to your car’s location in the lot, how are you able to recall the current spot? To retrieve today’s park- ing spot, your memory system must discriminate that target memory from many related, competing memories. Research has suggested that such discrimination is facilitated by the inhibition of competing memories, and that such inhibition has lasting effects. Anderson, Bjork, and Bjork (1994) demonstrated that retrieving a memory results in reduced subsequent recall for related memories. Their participants were required to study a set of category-exemplar pairs (e.g., Fruit-Apple, Fruit- Orange, Tool-Hammer, Tool-Wrench). The study phase provided equal encoding for all items. During a retrieval practice phase, half of the exemplars in half of the catego- ries were practiced in a category-and-stem-cued recall task (e.g., Fruit-Or____ cued Orange). Thus, there were prac-