1 Interference Resolution in Retrieval-Induced Forgetting : Behavioral

Retrieving memories renders related memories less accessible. This phenomenon, termed retrieval-induced forgetting (RIF), is thought to be the result of processes that resolve interference during competitive retrieval. Several studies have manipulated the level of interference to test different theoretical accounts of RIF (e.g. inhibitory vs. non-inhibitory). However, the nature of how interference and RIF are related has not been systematically investigated. Here, we introduce a design that allows for assessing interference during competitive retrieval through measuring recall RTs associated to target recall. Using such a design, we found that RIF occurred only when interference during competitive retrieval reached moderate levels, but not when it was too low or too high. This finding might indicate that low levels of interference do not trigger interference resolution, whereas interference resolution might fail when interference reaches extremely high levels. Keywords: retrieval, forgetting, retrieval-induced forgetting, interference, inhibition Running head: INTERFERENCE RESOLUTION DURING RETRIEVAL 3 Interference Resolution in Retrieval-Induced Forgetting: Behavioral evidence for a nonmonotonic relationship between interference and forgetting Interference as a cause of forgetting has long captured the interest of scholars of memory. One specific question that has resurfaced in scientific discussions concerns the way interference during memory retrieval is resolved (for a review of interference theories from this perspective, see for instance Anderson & Bjork, 1994). The focus in these discussions was not solely on how interference causes memory failures during retrieval. Rather, it centred around the consequences of interference resolution. What happens to memory representations when a target memory is to be retrieved in the face of competing memories? How do we achieve retrieval of the correct target memory, and what happens to competing memories? In a seminal paper, Anderson (2003) suggested an executive process – analogous to response override – that resolves interference by weakening memory representations that interfere with target memories at the time of recall. This weakened representation would be evident in the decreased probability of recall of the interfering memory when it is tested at a later time. This model was the first to hypothesize an active executive process that can act to weaken memory representations so that these memories become less accessible for retrieval. Early on, Anderson, Bjork, and Bjork (1994) devised a procedure, the retrieval practice paradigm, that could separate a recall phase at time t, when interference from competing memories has to be resolved, from a recall phase at time t+1, when the accessibility of these competing memory representations can be measured. In this paradigm, participants are shown several category–member word pairs (e.g. animal–tiger, furniture– couch, animal–chicken, etc.) then practice retrieval of half of the members from half of the categories with category plus stem cues (e.g. animal – ti.? ). Anderson and colleagues (1994) reasoned that, during retrieval practice, non-practiced members of practiced categories (e.g. chicken) interfere with the recall of practiced members, and therefore have to be inhibited. Running head: INTERFERENCE RESOLUTION DURING RETRIEVAL 4 This should be evident from later testing, and that is exactly what they found: participants’ recall of non-practised members of practised categories was worse than their recall of members of categories that had not appeared in the retrieval practice phase. Anderson and colleagues (1994) termed this effect retrieval-induced forgetting (RIF). Inhibition, in this theoretical approach, is a process that operates when a relatively strong competing item interferes with the retrieval of a target memory. This approach involves three testable properties of RIF that are relevant for our study. First, RIF is interference-dependent, i.e., only items interfering with the retrieval of a target memory would suffer inhibition. Second, RIF is retrieval specific, i.e., manipulating target strength without retrieval of the target does not induce competition-based forgetting. Third, RIF is strength-independent, i.e., even when targets are retrieved, target strength does not influence RIF (e.g. Anderson, 2003). Together, these assumptions imply that RIF is the product of executive processes that resolve interference during competitive retrieval. The Relationship Between Interference and Interference Resolution Although interference dependence of RIF seems to be well established, we know little about how interference resolving processes operate in the face of increasing interference. Proponents of different inhibitory accounts of RIF conceive this relationship quite differently. Anderson (2003, p. 421) suggests that: ‘The more strongly associated to the category an unpracticed competitor was, the more impairment was found’. This implies a linear function between interference and the result of inhibition: the more an item interferes with retrieval, the more inhibition it suffers. Bäuml, Pastötter, and Hanslmayr (2010, p. 1049) suggest that ‘very low levels of interference may not trigger inhibitory processes when competing material is retrieval practiced’, but otherwise the strength of interference a competing item causes during retrieval has only a minor role in defining the level of forgetting. In their interpretation, inhibition Running head: INTERFERENCE RESOLUTION DURING RETRIEVAL 5 would be a process that kicks in only when interference reaches a certain threshold. They also theorise that, over this threshold level, the effect of inhibition does not change significantly with increasing interference. Norman and colleagues (2007) programmed a neural network model of RIF in which increasing competitor strength increases the effect of inhibition, but, over a certain point, can lead to a decrease in its success, (i.e., a decrease in RIF). Similarly, Anderson and Levy (2010) suggested that there is a positive linear relationship between the level of interference and inhibition demand, and a negative linear relationship between the level of interference and inhibition success. Together, these opposing relationships lead to a demand-success trade-off where very low levels of interference do not lead to RIF because the level of inhibition demand remains low, whereas interference can reach a level over which inhibition cannot be effective, resulting in above baseline facilitation of competitors. The carryover assumption put forward by these authors states that RIF would be seen only for items that induce moderate levels of interference. The lack of knowledge about the function relating interference to forgetting makes it hard to design tests that try to tap properties of RIF. Take a study that tries to provide evidence for interference dependence by including a group of items with strong taxonomic frequency (supposedly inducing large interference) and another with low taxonomic frequency (supposedly inducing small interference) (e.g. Anderson et al., 1994; Williams & Zacks, 2001). This study would reliably provide significant RIF differences between these two groups if the relationship between interference and forgetting was a simple linear one, as suggested by Anderson (2003). In the case of a threshold-like interference resolution process, suggested by Bäuml et al. (2010), differences will only be found if the low taxonomic frequency words do not achieve a certain threshold where inhibition kicks in. Moreover, if inhibition causes forgetting to decrease over a certain level of interference, as predicted by Running head: INTERFERENCE RESOLUTION DURING RETRIEVAL 6 Norman et al. (2007) and Anderson and Levy (2010), one might see no differences between the two groups because one of them does not cause interference at all, while the other one causes too much interference. Studies using factorial designs might obtain contradictory results (see, for instance, Anderson et al. (1994) vs. Williams & Zacks (2001)) simply because the groups of words chosen to be causing large or small interference are chosen on an arbitrary basis and without any knowledge of the underlying relationship between interference and the effect of interference resolution. Another advantage of understanding how the effect of interference resolution changes as interference increases would be to design tests that are more sensitive to detect RIF. Such tests could focus only on memories that truly caused interference during memory retrieval, and thus are expected to suffer the results of interference resolution. Such sensitive tests would be very useful in settling some hot debates about the nature of interference resolving processes in memory, e.g. to clarify whether RIF generalises to novel, independent cues (for positive evidence see e.g. Aslan, Bäuml, & Pastötter, 2007, Levy, McVeigh, Marful, & Anderson, 2007; Saunders & MacLeod, 2006, for negative evidence see e.g. Camp et al., 2007; Perfect et al., 2004). Item-by-Item RIF Our goal in this study was to develop a test that can give an indication of how RIF changes as a function of competition during retrieval. Therefore, we needed a design that could provide data on how retrieval of each memory item is affected by interference during the retrieval practice phase. We set two objectives to achieve this goal. First, the design should be such that each item has an individual competitor which interferes with it. Second, we needed to collect data that at least indirectly informs us about the amount of interference a memory item suffers during its retrieval in the retrieval practice phase. For this second Running head: INTERFERENCE RESOLUTION DURING RETRIEVAL 7 purpose we chose reaction times (RTs) of target memory retrieval during the retrieval practice phase. Reaction times have been used to measu