Forgetting unwanted memories: directed forgetting and thought suppression methods

Experimental psychopathologists have tested hypotheses regarding mechanisms that ought to be operative if victims possess skills for forgetting material related to trauma. In this article, we review research on directed forgetting and thought suppression paradigms, concentrating on laboratory studies involving attempts by individuals reporting trauma histories to forget emotionally negative material. Most studies have shown that trauma survivors, especially those with post-traumatic stress disorder, are characterized by a breakdown in the ability to forget disturbing material. Studies on individuals reporting repressed or recovered memories of trauma have not confirmed predictions regarding heightened forgetting skills for trauma-related words. However, recent research on suppressing disturbing autobiographical memories suggests that people who report spontaneously recalling childhood abuse outside of psychotherapy may, indeed, possess skills for not thinking about disturbing material.     

Automatic retrieval in directed forgetting

In two experiments, we investigated the role of automatic retrieval in directed forgetting, using a stem completion test. In each experiment, we compared the performance of an implicit group, a process dissociation procedure (PDP) group, and a group given a speeded response task. The response times of the speeded response group on the stem completion task replicated earlier data in suggesting that this group adopted a purely automatic retrieval strategy. Experiment 1 revealed a directed-forgetting effect on automatic retrieval with the item method, but Experiment 2 revealed no directed-forgetting effect on automatic retrieval with the list method, consistent with the lack of implicit effects with the list method throughout the literature. Both experiments showed lower automatic estimates for the PDP group than for the implicit and speeded response groups, which did not differ. The data are consistent with either a selective rehearsal or an inhibition account of directed forgetting with the list method. The comparison of methods for assessing automatic retrieval is consistent with earlier evidence suggesting that subjects may adopt a generate/recognize strategy when given direct retrieval instructions.     

定向遗忘的编码加工机制

有目的的遗忘(定向遗忘)需要耗费认知努力吗?有研究发现, 定向遗忘可能是被动衰减的结果, 即F项目(需要遗忘的项目)未获得有效复述是选择性复述了R项目(需要记住的项目)造成的, 这一加工过程不需要认知努力; 但也有研究表明, 定向遗忘过程可能是遗忘线索诱发的对记忆加工的主动抑制, 需要耗费认知努力, 脑认知研究中发现的前额叶ERPs成分为这一机制提供了证据。还有一种观点认为, 定向遗忘编码过程可能同时包含主动抑制与被动衰减, 但是尚不清楚两种加工机制相互作用的方式。为进一步澄清定向遗忘编码阶段的认知机制, 未来研究需要将非认知因素纳入考察, 并关注不同人群的定向遗忘特征, 在此基础上尝试解决理论争议。     

Unblocking memory through directed forgetting

The ability to remember an item can be blocked, or negatively primed, by exposure to related items. For example, ALLERGY is less likely to be generated given the word fragment A_L_ _GY if one is first exposed to ANALOGY. We examined whether this memory blocking effect is influenced by list-method directed forgetting. A total of 144 participants learned two lists of items, each consisting of words that were designed to negatively prime performance on a subsequent word fragment completion task. Participants who were told to forget List 1 before learning List 2 suffered significantly less memory blocking owing to the negative primes from List 1 than participants who were told to remember List 1. These results suggest that directed forgetting can modify the memory blocking effect by affecting the accessibility of information in memory.     

Metacognition influences item-method directed forgetting

In 4 experiments, we examined whether metacognitive beliefs about item memorability influence item-method directed forgetting. In Experiment 1, participants studied loud and quiet items, which were subsequently cued as to-be-remembered (TBR) or to-be-forgotten (TBF). Typically, the volume of stimuli does not influence recall, although loud items are judged as more memorable than quiet items (Rhodes & Castel, 2009). In contrast, we found a recall advantage for loud items in directed forgetting, although this was observed for TBR items but not TBF items. The loud item advantage disappeared in Experiment 2, when we eliminated all TBF trials and instead inserted additional trials during which participants could engage in extra rehearsal of earlier presented items. In Experiments 3 and 4, a recall advantage for loud items was observed again when items were assigned a mixture of positive and negative values, but it did not emerge when items were assigned graded positive values. Overall, the results showed that the recall advantage for loud items emerges only in response to the need to forget some items. We propose 2 mechanisms to account for these results-either participants select to rehearse loud items as a controlled strategy that allows them to forget some items, or they have an unconscious preference for loud items that emerges only in response to the need to forget. (PsycINFO Database Record (c) 2012 APA, all rights reserved).     

Impaired directed forgetting in abstinent heroin addicts

Drug-related memories persist long into abstinence and are potent elicitors of drug craving and relapse. We report two experiments examining whether heroin-dependent individuals are impaired in intentionally suppressing drug-related memories. Experiment 1 adopted the Item paradigm where addicts and healthy controls were presented with a list of words each followed by a remember or forget cue. Experiment 2 adopted the List paradigm where they studied one list of items and were then split into a remember group and a forget group. Both groups studied a second list, except that the forget group was told to forget the first list. Compared with controls, addicts showed a reduced directed forgetting effect in the Item method and a total absence of one measure of directed forgetting in the List method (List 2 benefits). Results indicate that heroin addicts are impaired in directed forgetting and that the deficits are likely associated with memory encoding as opposed to retrieval. Possible problems include reduced ability in actively suppressing/stopping encoding of irrelevant information into memory or inability in changing/resetting encoding strategies. In neither experiment did the addicts show any differential directed forgetting effects between drug-related words and neutral words, indicating the generic nature of their intentional forgetting deficits.     

The crucial role of postcue encoding in directed forgetting and context-dependent forgetting

People can intentionally forget previously studied material if, after study, a forget cue is provided and new material is learned. It has recently been suggested that such list-method directed forgetting arises because the forget cue induces a change in internal context and causes context-dependent forgetting of the studied material (L. Sahakyan & C. M. Kelley, 2002). The authors compared directed forgetting and context-dependent forgetting by examining whether, like a forget cue, a change in internal context needs subsequent learning of new material to be effective. Participants studied an item list and, after study, received a remember cue or a forget cue or their internal context was changed through an imagination task. In each condition, half the participants learned a second list, and the other half fulfilled an unrelated distractor task. Both the forget cue and the change in internal context induced forgetting of the first list only when learning of the second list was interpolated. These results suggest that postcue encoding of new material is crucial for both directed forgetting and (some forms of) context-dependent forgetting.     

Evidence for age-related equivalence in the directed forgetting paradigm

The directed forgetting paradigm involves, under particular experimental circumstances, inhibitory mechanisms, which operate to the successful forgetting of irrelevant words. The item-by-item cueing method (e.g., Basden & Basden, 1996) was used to investigate the directed forgetting effect in young and old adults. Processing of the experimental words was manipulated between subjects by asking participants to perform either a deep or a shallow orienting task on each word of the study list before the occurrence of the cue (to remember of to forget). Results indicated that the instruction to process deeply both to-be-remembered and to-be-forgotten words led to equivalent directed forgetting effects in young and old adults. These results are discussed with respect to the implications they have for the Inhibitory Deficit theory (e.g., Hasher & Zacks, 1988), which suggests that cognitive aging is mainly characterized by a reduction in the efficiency of inhibitory processes.     

Pre-experimental sleep effects on directed forgetting

A directed forgetting (DF) paradigm was used to compare the remembering and forgetting of participants with good sleep quality to those with poor sleep quality and the presence of insomnia symptoms. This study implemented a point system in place of remember and forget instructions in a DF task with the goal of computing DF costs and benefits. Relations among memory, sleep, and working memory capacity (WMC) were also examined. DF benefits were observed in both groups, with negative costs found for participants without the presence of insomnia symptoms. WMC was found to be related to memory for positive point items only, and did not differ based on sleep quality. These results suggest that the presence of self-reported insomnia symptoms does not affect performance on a DF task.     

Divided attention facilitates intentional forgetting: evidence from item-method directed forgetting

This study examined the effects of post-cue interval and cognitive load on item-method directed forgetting. The results of Experiment 1 (free recall test) and Experiment 2 (cued recall test) showed that forget item retention increased as the post-cue interval increased. Moreover, increasing the cognitive load of participants by asking them to perform a secondary counting task did not impair, but rather facilitated, the intentional forgetting of the studied item under long post-cue interval conditions. These results and analyses of recall gains from the additional use of the independent cue suggest that the improved recall of forget items caused by an increase in the post-cue interval came from an automatic process, and that after receiving the forget cue, participants did not engage a suppression operation that was resource-demanded. The current findings suggest that forgetting is more effective when participants perform a secondary task after receiving the forget cue.     

Local context effects during emotional item directed forgetting in younger and older adults

This paper explored the differential sensitivity young and older adults exhibit to the local context of items entering memory. We examined trial-to-trial performance during an item directed forgetting task for positive, negative, and neutral (or baseline) words each cued as either to-be-remembered (TBR) or to-be-forgotten (TBF). This allowed us to focus on how variations in emotional valence (independent of arousal) and instruction (TBR vs. TBF) of the previous item (trial n-1) impacted memory for the current item (trial n) during encoding. Different from research showing impairing effects of emotional arousal, both age groups showed a memorial boost for stimuli when preceded by items high in positive or negative valence relative to those preceded by neutral items. This advantage was particularly prominent for neutral trial n items that followed emotional items suggesting that, regardless of age, neutral memories may be strengthened by a local context that is high in valence. A trending age difference also emerged with older adults showing greater sensitivity when encoding instructions changed between trial n-1 and n. Results are discussed in light of age-related theories of cognitive and emotional processing, highlighting the need to consider the dynamic, moment-to-moment fluctuations of these systems.     

Context-dependent impairment of recollection in list-method directed forgetting

In list-method directed forgetting, people's ability to forget one of the sets of learned material is examined. Research shows that memory for to-be-forgotten items is impaired when assessed by a recall test and by recognition tests reliant on recollective processes. Retrieval inhibition and context-change mechanisms have been proposed to account for the directed forgetting effects and both of them account for the results obtained with recognition tests. However, the context change account makes a specific prediction that recollection is impaired by directed forgetting only if it makes use of contextual associations. In the present study, directed forgetting was examined with two types of recollection-based tasks making use of different types of associations, namely a list discrimination task utilising contextual associations and an associative recognition task utilising interitem associations. Consistent with the context change account, the costs of directed forgetting were observed in a list discrimination task and were not observed in an associative recognition task. The results indicate that impairment in recollection due to directed forgetting is not general and provide converging evidence to support the context-change account.     

The role of retrieval practice in directed forgetting

Three experiments tested the possibility that retrieval-induced forgetting is responsible for directed forgetting with the list method. In Experiments 1 and 2, additional List 2 retrieval practice was given to determine whether this would increase directed forgetting. In Experiment 1 all items came from a single category, and in Experiment 2 unrelated words were used. In Experiment 3 additional List 2 study accompanied List 2 retrieval practice. There was no evidence that List 2 retrieval practice, with or without additional List 2 study, affected the magnitude of directed forgetting. It was argued that retrieval-induced forgetting could not account for these results. Accounts with greater viability include retrieval strategy disruption and a modified version of the dissociation hypothesis.     

Cease remembering: control processes in directed forgetting

On the premise that committing a word to memory is a type of covert action capable of being stopped, this study merged an item-method directed forgetting paradigm with a stop signal paradigm. The primary dependent measure was immediate recall. Indicating that participants were able to countermand the default instruction to remember, there was an overall directed forgetting effect, the magnitude of which varied as a function of forget signal delay. The results suggest that the covert act of intentionally forgetting may engage cognitive control processes at encoding that are analogous to those required to prevent the execution of prepotent overt responses.     

Brief wakeful resting can eliminate directed forgetting

When cued to intentionally forget previously encoded memories, participants typically show reduced recall of the memories on a later recall test. We examined how such directed forgetting is affected by a brief period of wakeful resting between encoding and test. Encoding was followed by a “passive” wakeful resting period in which subjects heard emotionally neutral music or perceived neutral pictures, or it was followed by an “active” distraction period in which subjects were engaged in counting or calculation tasks. Whereas typical directed forgetting was present after active distraction, the forgetting was absent after wakeful resting. The findings indicate that the degree to which people can intentionally forget memories is influenced by the cognitive activity that people engage in shortly after learning takes place. The results provide first evidence on the interplay between wakeful resting and intentional forgetting.     

Cognitive load hypothesis of item-method directed forgetting

This study examined the effect of the processing demands of to-be-remembered (TBR) words on item-method directed forgetting. Experiment 1 found that a standard memory group remembered fewer to-be-forgotten (TBF) words than a naming group, in which participants simply named the TBR words during the study phase, even though both groups were equally instructed to forget the TBF words. Experiment 2 manipulated the number of TBR words in the study list, keeping the number of TBF words constant, and found that TBF word forgetting was more difficult in the few TBR words condition than the more TBR words condition. The same pattern was found in the result of Experiment 3 when a cued recall test, instead of a free recall test, was used. In all the experiments, participants were asked to recall the TBF words before the TBR words. These findings are consistent with the cognitive load hypothesis that it is easier to forget when there are fewer cognitive resources available during encoding.     

Item method directed forgetting diminishes false memory

Directed forgetting may reduce the ORM false memory illusion by interfering with meaning processing. Participants were presented with a list composed of six 10-word semantically associated sub-lists, and they were either (a) asked to remember a ll list it ems or (b) asked to remember all associates from sub-lists and to forget all associates from other sub-lists. All participants were requested to recall and recognise list items. Although directed forgetting effects have been previously reported only for true responses in the ORM paradigm with the list method, we also found directed forgetting for false responses with the item method. Such forgetting instructions reduced both verbatim and meaning processing, decreasing both the intrusion and the false alarm rate. These results are consistent with two-process explanations of DRM false memories, such as fuzzy-trace theory, and add to our understanding of false memory editing.     

Cognitive load hypothesis of item-method directed forgetting

This study examined the effect of the processing demands of to-be-remembered (TBR) words on item-method directed forgetting. Experiment 1 found that a standard memory group remembered fewer to-be-forgotten (TBF) words than a naming group, in which participants simply named the TBR words during the study phase, even though both groups were equally instructed to forget the TBF words. Experiment 2 manipulated the number of TBR words in the study list, keeping the number of TBF words constant, and found that TBF word forgetting was more difficult in the few TBR words condition than the more TBR words condition. The same pattern was found in the result of Experiment 3 when a cued recall test, instead of a free recall test, was used. In all the experiments, participants were asked to recall the TBF words before the TBR words. These findings are consistent with the cognitive load hypothesis that it is easier to forget when there are fewer cognitive resources available during encoding.     

Item method directed forgetting diminishes false memory

Directed forgetting may reduce DRM false memory illusion by interfering with meaning processing. Participants were presented with a list composed of six 10-word semantically associated sub-lists, and they were either (a) asked to remember all list items of (b) asked to remember all associates from sub-lists and to forget all associates from other sub-lists. All participants were requested to recall and recognise list items. Although directed forgetting effects have been previously reported only for true responses in the DRM paradigm with the list method, we also found directed forgetting for false responses with the item method. Such forgetting instructions reduced both verbatim and meaning processing, decreasing both the intrusion and the false alarm rate. These results are consistent with two-process explanations of DRM false memories, such as fuzzy-trace theory, and add to our understanding of false memory editing.     

A contextual change account of the directed forgetting effect

The authors propose that the costs and benefits of directed forgetting in the list method result from an internal context change that occurs between the presentations of 2 lists in response to a "forget" instruction. In Experiment 1 of this study, costs and benefits akin to those found in directed forgetting were obtained in the absence of a forget instruction by a direct manipulation of cognitive context change. Experiment 2 of this study replicated those findings using a different cognitive context manipulation and investigated the effects of context reinstatement at the time of recall. Context reinstatement reduced the memorial costs and benefits of context change in the condition where context had been manipulated and in the standard forget condition. The results are consistent with a context change account of directed forgetting.