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.     

Affect influences false memories at encoding: evidence from recognition data

Memory is susceptible to illusions in the form of false memories. Prior research found, however, that sad moods reduce false memories. The current experiment had two goals: (1) to determine whether affect influences retrieval processes, and (2) to determine whether affect influences the strength and the persistence of false memories. Happy or sad moods were induced either before or after learning word lists designed to produce false memories. Control groups did not experience a mood induction. We found that sad moods reduced false memories only when induced before learning. Signal detection analyses confirmed that sad moods induced prior to learning reduced activation of nonpresented critical lures suggesting that they came to mind less often. Affective states, however, did not influence retrieval effects. We conclude that negative affective states promote item-specific processing, which reduces false memories in a similar way as using an explicitly guided cognitive control strategy.     

Individual differences in the suppression of unwanted memories: the executive deficit hypothesis

When confronted with reminders to an unpleasant memory, people often try to prevent the unwanted memory from coming to mind. In this article, we review behavioral and neurocognitive evidence concerning the consequences of exerting such control over memory retrieval. This work indicates that suppressing retrieval is accomplished by control mechanisms that inhibit the unwanted memories, making them harder to recall later, even when desired. This process engages executive control mechanisms mediated by the lateral prefrontal cortex to terminate recollection-related activity in the hippocampus. Together, these findings specify a neurocognitive model of how memory control operates, suggesting that executive control may be an important means of down-regulating intrusive memories over time. We conclude by proposing that individual differences in the regulation of intrusive memories in the aftermath of trauma may be mediated by pre-existing differences in executive control ability. In support of this executive deficit hypothesis, we review the recent work indicating links between executive control ability and memory suppression.     

Count out your intrusions: Effects of verbal encoding on intrusive memories

Peri-traumatic information processing is thought to affect the development of intrusive trauma memories. This study aimed to replicate and improve the study by Holmes, Brewin, and Hennessy (2004, Exp. 3) on the role of peri-traumatic verbal processing in analogue traumatic intrusion development. Participants viewed an aversive film under one of three conditions: counting backwards in 3s (“verbal interference”), verbalising emotions and thoughts (“verbal enhancement”), or without an extra task. A dual-process account of PTSD would predict that verbal interference would increase intrusion frequency compared to no task, whereas verbal enhancement would lead to a decrease. In contrast, mainstream memory theory predicts a decrease in intrusion frequency from any concurrent task that diverts attention away from the trauma film. The main finding was that the verbal interference task led to a decrease in intrusive memories of the film compared to the other two conditions. This finding does not support a dual-process account of PTSD, but is in line with general theories of memory and attention.     

Gaze bias: Selective encoding and liking effects

People look longer at things that they choose than things they do not choose. How much of this tendency—the gaze bias effect—is due to a liking effect compared to the information encoding aspect of the decision-making process? Do these processes compete under certain conditions? We monitored eye movements during a visual decision-making task with four decision prompts: Like, dislike, older, and newer. The gaze bias effect was present during the first dwell in all conditions except the dislike condition, when the preference to look at the liked item and the goal to identify the disliked item compete. Colour content (whether a photograph was colour or black-and-white), not decision type, influenced the gaze bias effect in the older/newer decisions because colour is a relevant feature for such decisions. These interactions appear early in the eye movement record, indicating that gaze bias is influenced during information encoding.     

Age differences in recollection: three patterns of enhanced encoding

Memory encoding conditions can be manipulated in a variety of ways, and many of these methods result in improved recollection for both younger and older adults relative to baseline conditions. Previous results have shown differential age-related patterns of improvement, however, with some manipulations giving equal improvement to young and old participants, some benefiting older adults more, and others benefiting younger adults more. In 2 experiments, the authors show that presenting pictures with words benefited older more than younger participants, word generation benefited both groups equally, and an encoding condition requiring novel integrative processing benefited younger more than older adults. The authors discuss these results in terms of the enhanced elaboration afforded and processing demanded by differential combinations of age groups and encoding conditions.     

Overgeneral memory and suppression of trauma memories in post-traumatic stress disorder

The study investigated the relationship between the suppression of trauma memories and overgeneral memory in 42 assault survivors with and without PTSD. Overgeneral memory (OGM) was assessed with a standard autobiographical memory test (AMT). Participants completed two further AMTs under the instructions to either suppress or not suppress assault memories, in counterbalanced order. Participants with PTSD retrieved fewer and more general memories when following the suppression instruction than participants without PTSD, but not under the control instruction. OGM correlated with PTSD symptom severity, and measures of cognitive avoidance. The results are discussed with reference to current theories of overgeneral memory and its possible relationship with PTSD.     

Role of cholinergic system on the construction of memories: taste memory encoding

There is a large body of evidence suggesting that cholinergic activity is involved in memory processes. It seems that cholinergic activity is essential to learn several tasks and recent works suggest that acetylcholine plays an important role during the early stages of memory formation. In this review, we will discuss the results related to taste memory formation, focusing particularly on the conditioned taste aversion paradigm. We will first give evidence that nucleus basalis magnocellularis is involved in taste memory formation, due to its cholinergic projections. We then show that the cholinergic activity of the insular (gustatory) cortex is related to the taste novelty, and that the cholinergic signals initiated by novelty are crucial for taste memory formation. Then we present recent data indicating that cortical activation of muscarinic receptors is necessary for taste trace encoding, and also for its consolidation under certain circumstances. Finally, interactions between the cholinergic and other neuromodulatory systems inducing intracellular mechanisms related to plastic changes will be proposed as important processes underlying gustatory memory trace storage.     

Increase in physiological inhibitory control results in better suppression of unwanted memories

Forgetting or suppressing a memory with unwanted content is just as important as remembering a desirable one. In addition to emphasizing the role of inhibitory control in memory suppression processes, neuropsychological studies have indicated that an intentional inhibition targeting a brain area may exert its inhibitory effects in seemingly unrelated areas through a common inhibitory network. In this study, we aimed to investigate whether the suppression of unwanted memories can be strengthened by recruiting an inhibitory task that can be simultaneously performed with a memory suppression task. Therefore, we manipulated the level of urinary urgency-induced inhibition of participants (N = 180) and test its effect on the suppression of unwanted memories using a Think/No-Think (T/NT) task. The results of our study indicated that individuals with high levels of urinary urgency demonstrated greater memory suppression compared to those with low urinary urgency. Findings and their implications are discussed within the context of cognitive and clinical perspectives, and recommendations are made for future research.     

Attempting suppression of traumatic memories over extended periods in acute stress disorder

This study investigated the influence of attempted suppression and thought control strategies on traumatic memories. Survivors of civilian trauma with acute stress disorder (ASD; n = 20) and without ASD (n = 20) monitored their trauma-related thoughts for three 24-h periods. In period 1, participants were instructed to think about anything. In period 2, participants were administered suppression or nonsuppression instructions relating to thoughts of the trauma. In period 3, participants were again instructed to think about anything. The results revealed no evidence for an increase in trauma-related thoughts following suppression instructions. Punishment and worry thought control strategies correlated significantly with both anxiety and suppression ratings. Frequency of intrusions was associated with a distraction cognitive strategy. These findings point to the importance of traumatised individuals' cognitive strategies in mediating the management and occurrence of posttraumatic intrusions.     

Internal languages of retrieval: The bilingual encoding of memories for the personal past

In contrast to most research on bilingual memory that focuses on how words in either lexicon are mapped onto memory for objects and concepts, we focus on memory for events in the personal past. Using a word-cue technique in sessions devoted exclusively to one language, we found that older Hispanic immigrants who had come to the United States as adults internally retrieved autobiographical memories in Spanish for events in the country of origin and in English for events in the U.S. These participants were consistently capable of discerning whether a memory had come to them "in words" or not, reflecting the distinction between purely imagistic or conceptual memories and specifically linguistic memories. Via examination of other phenomenological features of these memories (sense of re-living, sensory detail, emotionality, and rehearsal), we conclude that the linguistic/nonlinguistic distinction is fundamental and independent of these other characteristics. Bilinguals encode and retrieve certain autobiographical memories in one or the other language according to the context of encoding, and these linguistic characteristics are stable properties of those memories over time.     

Selective encoding in the interpretation of topographic maps

In two experiments, practised adult map users compared three-dimensional landsurface drawings against previously and separately studied contour maps. In the first experiment, adding extra contour levels, or marked drainage patterns, led to increased map study and decreased judgement times, whereas adding both led to no further increase or decrease respectively. In the second experiment, removing minor surface details from the drawings produced no overall variation in judgement times. These findings were taken as suggesting that map users selectively encode features from the map in task-determined fashion.     

Recall accuracy and illusory memories: when more is less

In two experiments it was revealed that manipulations that increased recall of studied list items also increased false recall of theme-related, critical nonpresented words. In Experiment 1 subjects listened to a series of short word lists, each containing items associatively related to a theme, while engaging in either semantic or nonsemantic processing. On an immediate free recall test semantic processors demonstrated greater correct recall as well as more illusory memories of critical nonpresented items than nonsemantic processors. In Experiment 2, the short study lists were combined to form longer lists that were presented either blocked by theme or in a random presentation order. Retention interval was also varied as participants were tested either immediately, one week after, or three weeks after the study phase. Presenting the target items in a blocked, as opposed to random, format increased recall accuracy, but this was at the expense of a higher intrusion rate for theme-consistent items. Interestingly, the level of false memories was not affected by retention interval even though typical decrements in the recall of study items were observed over time. The results of these experiments highlight the persistence of the false memory effect, as well as pointing to several factors, primarily semantic processing, that may lead to the creation of false memories. Interpretations are offered within the theoretical frameworks of source monitoring and fuzzy trace theory.     

Believing is seeing: how rumors can engender false memories in preschoolers

This study examined how an erroneous rumor circulated among preschoolers can influence their memory. One fourth of the children overheard a rumor from an adult conversation in which it was alleged that an event the children had not experienced themselves had occurred. A second fourth were the classmates of those who overheard the rumor. A third group had no exposure to the rumor. The remaining children actually experienced the event suggested by the rumor. One week later, the children were interviewed in either a neutral or a suggestive manner. Results from a second interview after a 2-week delay revealed that under both interview conditions, children who overheard the rumor, either from the adult conversation or during naturally occurring interactions with classmates, were as likely to report experiencing the rumored but nonexperienced event as were those who actually experienced it. Most reports of the rumored but nonexperienced event were in children's free recall and were accompanied by high levels of fictitious elaboration.     

Selective attention versus selection for action: negative priming is not the result of distractors being unattended

Using a novel referent size-selection task, MacDonald, Joordens, and Seergobin (1999; MacDonald & Joordens, 2000) found that negative priming persisted even when participants were encouraged to attend to distractors before selectively responding to targets. This finding suggested that negative priming is not caused by processes that operate on stimuli that are to be ignored in the traditional selective attention sense. Mackintosh, Mathews, and Holden's (2002) attempt to replicate the MacDonald et al. study resulted in the discovery of possible artifacts in the referent size-selection task, thereby making the implications with respect to the role of attention less clear. In the present study, we describe a different method for directing attention to distractors in a negative priming context, one that does not suffer from the same potential artifacts as the referent size-selection task. Our results are consistent with those found by MacDonald et al., in that negative priming persisted even when participants were explicitly encouraged to attend to distractors. Implications are discussed in the context of the related concepts of selective attention (e.g., Broadbent, 1965) versus selection for action (e.g., Allport, 1987).     

Failures to find suppression of episodic memories in the think/no-think paradigm

Anderson and Green (2001) had subjects learn paired associates and then selectively suppress responses to some of them. They reported a decrease in final cued recall for responses that subjectshad been instructed not to think of and explained their data as resulting from cognitive suppression, a laboratory analog of repression. We report three experiments designed to replicate the suppression/repression results. After subjects learned a series of A-B word pairs (e.g., ordsea-roach), they were then asked to respond to some items and not to think of other items when shown their cues 1, 8, or 16times. During a final recall test, they were cued with either asame (direct)probe (ordeal-__) or a n independent(indirect) probe (insect-r__) . None of our experiments showed reliable suppression effects with either the same or independent-probe tests. Suppression is apparently not a robust experimental phenomenon in the think/no-think paradigm.     

Valence of autobiographical memories: The role of mood, cognitive reappraisal, and suppression

The selective recall of positive memories is thought to be an effective mood repair technique, but little research has examined individual differences in the motivation or ability to implement this strategy. This study examined factors considered likely to impact valenced memory recall: dysphoria and emotion regulation strategies (i.e., cognitive reappraisal and suppression). Dysphoria was related to memory negativity but not positivity, whereas cognitive reappraisal was associated with positivity but not negativity. Suppression was not reliably related to the valence of self-reported memories, but was associated with increased accessibility of negative memories, as indicated by a response time measure. Our results indicate a relationship between cognitive reappraisal and more positive memory and suggest that the experience of dysphoria is more strongly related to negativity than positivity of memory. Our findings highlight the utility of examining emotion regulatory variables, in addition to mood, in the study of valenced memory recall, and underscore the importance of including both behavioral and self-report memory measures.     

Forgetting to forget: On the duration of voluntary suppression of neutral and emotional memories

Can we control the content of our memory and forget what we do not want to think about by an act of will? If so, is forgetting temporary or permanent, and is it independent of the nature of what we wish to forget? Using Anderson and Green’s (2001) “think/no-think” paradigm with neutral and emotional nouns, we found in agreement with other studies that memory for neutral words was reduced instantly upon repeated attempts at suppression. However, the effect was temporary and vanished after a period of one week, which strongly suggests that intended memory suppression interferes with immediate retrieval but does not lead to long-term forgetting. Furthermore, the amount of training that clearly reduced immediate recall of neutral items did not at all reduce recall of emotional items. This finding is in accordance with the notion that emotional items have a higher degree of salience and tend to attract more attention than neutral items.     

Modelling response selection in task switching: Testing the contingent encoding assumption

The contingent encoding assumption is the idea that response selection in task-switching situations does not begin until the cue and the target have both been encoded. The authors tested the assumption by manipulating response congruency, stimulus order, and stimulus onset asynchrony (SOA) in two experiments. They found evidence of response selection prior to cue encoding for congruent targets with target–cue order at a long SOA, indicating that the contingent encoding assumption is invalid. The authors describe how contingent encoding can be removed from an existing task-switching model by introducing baseline evidence—task-neutral evidence that serves as a baseline for response selection prior to stimulus encoding. Simulations revealed that the modified model could reproduce the full pattern of response time data and generate responses prior to cue encoding. The authors conclude by discussing directions for further model development.