Running head: MEMORY UNITIZATION AND RIF 1 MEMORY UNITIZATION AND RETRIEVAL-INDUCED FORGETTING FOR DRM WORD LISTS

As a target memory is recalled or practiced, its competitors are suppressed, making them more difficult to recall in future attempts. This is called retrieval-induced forgetting (RIF; Anderson, Björk, & Björk, 1994), and is evidenced by lesser recall for unpracticed members of a partially practiced list (RPitems) than for members of an unpracticed list (NRP items). The RIF effect, while extremely robust, is not immutable. Directed integration of items into a unified knowledge structure has been shown to greatly reduce or even eliminate the RIF effect (Anderson & McCulloch, 1999). Additionally, high associate word lists, those with greater semantic relatedness, have been shown to result in spontaneous integration (Bäuml & Kuhbandner, 2003). In this study, we combined these factors, along with delay, into a 3 x 2 x 2 x 2 (integration x associativity x delay x set) mixed-model design, using Deese-Roediger-McDermott (DRM) word lists (Stadler, Roediger, & McDermott, 1999), in order to examine the operation of these mediating factors. While set (RIF effect) and delay were statistically significant, we observed no main effects of either integration or associativity. Additionally, there were no statistically significant interactions, indicating that RIF can be robust even to those factors, like integration and associativity, which under certain circumstances reduce its effects. MEMORY UNITIZATION AND RIF 4 Memory Unitization and Retrieval-induced forgetting for DRM Word Lists Human memory has a remarkably large capacity and our ability to quickly and accurately retrieve target memories amidst a sea of competitors is nothing short of astounding. Recently, research has turned to examining the specific characteristics of retrieval processes that allow our memory systems to perform at this level. Anderson, Bjork, and Bjork (1994) postulated that a process of inhibition is incumbent within our memory system; when individuals retrieve a target memory, they necessarily inhibit its numerous competitors. This allows for the speed and precision displayed by our memory systems despite their operation within a complex retrieval environment. Inhibitory processes, however, do not exist without drawbacks. Those items in direct competition with a target item are suppressed in order to expedite access to the target items, but this suppression lingers beyond one specific act of retrieval. Future attempts to retrieve the previously inhibited items will be less successful than if they had not been inhibited, evidenced by stronger recall performance on unrelated than inhibited items. Anderson and colleagues termed this effect retrieval-induced forgetting (RIF). Theoretically, RIF occurs under every circumstance of partial recall of a related list (Anderson et al., 1994). In RIF research, relatedness is typically, though not necessarily, semantic. Anderson and colleagues (1994) developed a three-step methodological paradigm expected to reliably reproduce the RIF effect. This paradigm consists of a study phase, wherein individuals are introduced to the totality of the body of related items, a retrieval-practice phase, wherein individuals practice retrieving a subset of the items in the items, and a test phase wherein individuals are asked to recall as many of the list items as they can. To simplistically illustrate this paradigm in a way directly relevant to the current study, an individual might be given a list of category – exemplar word pairs from varying categories during the study phase. MEMORY UNITIZATION AND RIF 5 After the study phase, they would engage in retrieval practice of a subset of the items. Typically, they would be given word stems (e.g., COLD – free_ _), in order to facilitate the retrieval of target (RP+) items in the list (i.e., freeze). In the test phase, the RIF effect would account for better overall performance on unpracticed, unrelated (NRP) items (e.g., CHAIR – couch) than on unpracticed, related (RP-) items (e.g., COLD – ice) which have been inhibited in order to facilitate retrieval of the target items. This variance in performance is due to the suppression of the unpracticed, related (RP-) item at the retrieval practice phase, and the tendency for this suppression to remain well beyond the specific retrieval trial. Most importantly for the current study, RIF is not uniform. It varies with the presentation or removal of specific conditions during the study and retrieval practice phases. For example, MacLeod and Macrae (2001) failed to observe RIF when introducing a 24 hour delay between the retrieval practice phase and the test phase, despite the fact that the same conditions produced RIF when tested immediately. MacLeod and Macrae concluded that RIF is transient, or quicklydisappearing. In other contexts, RIF can be extremely robust and insensitive. For example, Storm, Bjork, and Bjork (2012) observed continuing RIF for delays of up to one week. Conflicting findings like these are common within the RIF literature, perhaps indicating that RIF is erratic in its appearance and disappearance. Rather than thinking of RIF as transient, we would perhaps better conceive of it as fickle. Rather than being short-lasting, RIF is instead long lasting, but is very susceptible to minute situational variations which might make it appear shortlasting. Several mediating factors, namely integration, associativity, and delay, have been tested and identified in terms of their mitigating effect on RIF.