The impact of retrieval suppression on conceptual implicit memory

ABSTRACT

When people suppress retrieval of episodic memories, it can induce forgetting on later direct tests of memory for those events. Recent reports indicate that suppressing retrieval affects less conscious, unintentional retrieval of unwanted memories as well, at least on perceptually-oriented indirect tests. In the current study we examined how suppressing retrieval affects conceptual implicit memory for the suppressed content, using a category verification task. Participants studied cue-target words pairs in which the targets were exemplars of 22 semantic categories, such as vegetables or occupations. They then repeatedly retrieved or suppressed the targets in response to the cues for some of those pairs. Afterwards, they were exposed to the targets intermixed with novel items, one at a time, and asked to verify the membership of each of the words in a semantic category, as quickly as possible. Judgment response times to studied words were faster than to unstudied exemplars, reflecting repetition priming, as has been previously observed. Strikingly, the beneficial effects of prior exposure on response time were eliminated for targets that had been suppressed. Follow-up explicit memory tests also demonstrated that retrieval suppression continued to disrupt episodic recall for the items that had been just been re-exposed on the category verification test. These findings support the contention that the effects of retrieval suppression are not limited to episodic memory, but also affect indirect expressions of those memories on conceptually oriented tests, raising the possibility that underlying semantic representations of suppressed content are affected.     

False working memories? Semantic distortion in a mere 4 seconds

False memories are well-established, episodic memory phenomena: Semantically related associates are confidently and erroneously remembered as studied items. We report four experiments yielding similar effects in a working memory paradigm. Four semantically related words were retained over a brief interval. Whether or not the interval was filled with a math verification task, semantically related lures were mistakenly recognized as members of the memory set and took longer to reject than did unrelated negative probes. In a short-term recall task, semantic intrusions exceeded other errors (e.g., phonemic). Our results demonstrate false memory effects for a subspan list when a mere 4 sec was given between study and test. Such rapid semantic errors presumably result from associative processing, may be related to familiarity-based proactive interference in working memory, and are consistent with recent models that integrate short- and long-term memory processes.     

The use of source memory to identify one's own episodic confusion errors

In 4 category cued recall experiments, participants falsely recalled nonlist common members, a semantic confusion error. Errors were more likely if critical nonlist words were presented on an incidental task, causing source memory failures called episodic confusion errors. Participants could better identify the source of falsely recalled words if they had deeply processed the words on the incidental task. For deep but not shallow processing, participants could reliably include or exclude incidentally shown category members in recall. The illusion that critical items actually appeared on categorized lists was diminished but not eradicated when participants identified episodic confusion errors post hoc among their own recalled responses; participants often believed that critical items had been on both the incidental task and the study list. Improved source monitoring can potentially mitigate episodic (but not semantic) confusion errors.     

Destination and source memory in Huntington's disease

Destination memory refers to the recall of the destination of previously relayed information, and source memory refers to the recollection of the origin of received information. We compared both memory systems in Huntington's disease (HD) participants. For this, HD participants and healthy adults had to put 12 items in a black or a white box (destination task), and to extract another 12 items from a blue or a red box (source task). Afterwards, they had to decide in which box each item had previously been deposited (destination memory), and from which box each item had previously been extracted (source memory). HD participants showed poorer source as well as destination recall performance than healthy adults in the proposed tasks. Correlation analysis showed that destination recall was significantly correlated with episodic recall in HD participants. Destination memory impairment in HD participants seems to be considerably influenced by their episodic memory performance.     

The temporal contiguity effect predicts episodic memory performance

One way to study the associative processes at work during episodic memory is to examine the order of participant responses, which reveal the strong tendency to transition between temporally contiguous or semantically proximal items on the study list. Here, we assessed the correlation between participants’ recall performance and their use of semantic and temporal associations to guide retrieval across nine delayed free recall studies. The size of the participants’ temporal contiguity effects predicted their recall performance. When interpreted in terms of two models of episodic memory, these results suggest that participants who more effectively form and retrieve associations between items that occur nearby in time perform better on episodic recall tasks. Sample code may be downloaded as a supplement for this article from http://mc.psychonomic-journals.org/content/ supplemental.     

Variation in working memory capacity and episodic memory: Examining the importance of encoding specificity

In the present study, we examined the extent to which encoding specificity influences the relation between individual differences in working memory capacity (WMC) and episodic recall. Participants performed a paired associates cued recall task in which a rhyme or a semantic judgment was made during encoding. During recall participants were presented with the cue word along with either a rhyme or semantic cue. Across both rhyme and semantic conditions, encoding and retrieval conditions either matched or mismatched. When encoding and retrieval conditions matched, high WMC individuals outperformed low WMC individuals. When encoding and retrieval conditions mismatched, high and low WMC individuals performed equivalently. Importantly, this occurred because high WMC individuals were hurt more than low WMC individuals when conditions mismatched. These results demonstrate the importance of encoding specificity in the relation between WMC and episodic recall as well as of unifying prior work that has demonstrated that high WMC individuals are hurt more in some recall conditions than are low WMC individuals.     

Separating item-related electrophysiological indices of retrieval effort and retrieval orientation

The relationship between two classes of retrieval process-retrieval orientation and retrieval effort-was investigated using electrophysiological (ERP) and behavioural measures. ERPs were recorded during retrieval phases of exclusion tasks in which participants focused on retrieval of either phonological or semantic associates that were generated in a prior study phase. Participants were separated into two groups on the basis of the relative accuracy of their memory judgments in the retrieval tasks (high vs. low relative difficulty) as a means of assessing retrieval effort. The critical contrasts were between the ERPs evoked by unstudied test items separated according to group and emphasis of the retrieval task (semantic vs. phonological). Reliable differences according to task were evident in the high relative difficulty group only. This finding is consistent with the view that, for this task pair at least, ERPs are sensitive to the processes set in train in pursuit of task relevant information (retrieval orientations) only when relative difficulty is high.     

Semantic generation can cause episodic forgetting

The repeated retrieval of a subset of previously learned items can cause forgetting of the nonretrieved items. The study reported here investigated whether retrieval-induced forgetting generalizes to a situation in which the retrieved and nonretrieved items are not part of the same experiential episode and task. Subjects learned an item list that they had to recall later in the experiment. In a separate intermediate phase, they repeatedly generated related items from semantic memory, or were presented the same items intact for study. Only the semantic generation of items, and not their presentation for study, induced forgetting of the initially learned items. This result indicates that, first, semantic generation can cause recall-specific episodic forgetting and, second, retrieval-induced forgetting can occur even if the retrieved and nonretrieved items belong to different experiential episodes and tasks. Connections of the present results to other memory phenomena, such as part-set cuing and the generation effect, social cognition, and eyewitness memory, are discussed.     

Anticipation boosts forgetting of voluntarily suppressed memories

The role of anticipatory mechanisms in human memory control is poorly understood. Addressing the issue we investigated whether the presence of an anticipatory phase can enhance effects of cognitive control, as they occur during voluntary suppression of episodic memories. Using the Think/No-Think task, participants first learned several face–word associations, and thereafter were asked to either recall (think) or suppress (no-think) the word when provided with the word's face cue. In the one condition participants performed the Think/No-Think task in the presence of an anticipatory phase, giving participants the chance to prepare for memory suppression. In the other condition participants performed the task without such an anticipatory phase. On the final cued recall test participants were asked to recall all of the previously studied words. The results showed stronger forgetting of to-be-suppressed items in the presence than absence of the anticipatory phase. The finding is first evidence for the effectiveness of anticipatory mechanisms in human memory suppression.     

The role of inhibitory processes in part-list cuing

Providing a subset of studied items as retrieval cues can have detrimental effects on recall of the remaining items. In 2 experiments, the authors examined such part-list cuing impairment in a repeated testing situation. Participants studied exemplars from several semantic categories and were given 2 successive cued-recall tests separated by a distractor task of several minutes. Part-list cues were provided in the 1st test but not the 2nd. Noncue item recall was tested with the studied category cues (same probes) in the 1st test, but novel, unstudied retrieval cues (independent probes) in the 2nd test. The authors found detrimental effects of part-list cues in both the 1st (same-probe) test and the 2nd (independent-probe) test. These results show that part-list cuing impairment can be lasting and is not eliminated with independent probes. The findings support the view that the impairment was caused by retrieval inhibition.     

Retrieval during learning facilitates subsequent memory encoding

In multiple-list learning, retrieval during learning has been suggested to improve recall of the single lists by enhancing list discrimination and, at test, reducing interference. Using electrophysiological, oscillatory measures of brain activity, we examined to what extent retrieval during learning facilitates list encoding. Subjects studied 5 lists of items in anticipation of a final cumulative recall test and did either a retrieval or a no-retrieval task between study of the lists. Retrieval was from episodic memory (recall of the previous list), semantic memory (generation of exemplars from an unrelated category), or short-term memory (2-back task). Behaviorally, all 3 forms of retrieval enhanced recall of both previously and subsequently studied lists. Physiologically, the results showed an increase of alpha power (8-14 Hz) from List 1 to List 5 encoding when no retrieval activities were interpolated but no such increase when any of the 3 retrieval activities occurred. Brain-behavior correlations showed that alpha-power dynamics from List 1 to List 5 encoding predicted subsequent recall performance. The results suggest that, without intermittent retrieval, encoding becomes ineffective across lists. In contrast, with intermittent retrieval, there is a reset of the encoding process for each single list that makes encoding of later lists as effective as encoding of early lists.     

Inadvertent plagiarism in young and older adults: The role of working memory capacity in reducing memory errors

Two experiments examined inadvertent plagiarism in young and older adults. Young and older adults took turns generating category exemplars in small groups, and after a short retention interval recall was tested and subjects were asked to generate new exemplars (i.e., exemplars not initially generated). When asked to generate new exemplars, older adults were more likely to repeat exemplars that had been generated earlier by others (i.e., generate-new plagiarism). When asked to recall the exemplars they had generated earlier, older adults were more likely to claim that they had generated exemplars that had been generated by others (i.e., recall-own plagiarism), and were also more likely to falsely recall exemplars that had not been generated at all. There were no age differences in confidence for items that were plagiarized on the generate-new task. Hierarchical regression analyses indicated that age differences in generate-new plagiarism and false recall were entirely mediated by measures of episodic recall and working memory capacity. We conclude that inadvertent plagiarism errors result from the failure of systematic decision processes, and that controlled attention is important for avoiding memory errors.     

Semantic similarity and immediate serial recall: Is there an effect on all trials

In immediate serial recall, items are better recalled when they are all drawn from the same semantic category. This is usually accounted for by a two-stage retrieval-based framework, in which, at recall, long-term knowledge is used to reconstruct degraded phonological traces. The category shared by list items would serve as an additional retrieval cue restricting the number of recall candidates. Usually, the long-term search set is not defined, but some authors have suggested an extended search set and others a restricted set that is composed of the most recently presented items. This was tested in an experiment in which participants undertook an immediate serial recall task either alone or under articulatory suppression with either semantically similar or dissimilar lists. A trial-by-trial analysis revealed that, in both quiet and suppression conditions, items from similar lists were better recalled on all the trials, including the first one. In addition, there was no interaction between semantic similarity and trial, indicating that the effect of similarity was of similar size on all the trials. The results are best interpreted within a proposal suggesting an extended long-term search set.     

Intention superiority effect on implicit memory of shopping lists: Activation and inhibition processes

Intentional memory is defined as the ability to remember to perform intentions in the future. Forming an intention such as “shopping” activates access to memories related to the products on the shopping list. As Intention Superiority Effect (ISE) studies show, these memories are more accessible in semantic and episodic memory, more activated over time and protected from competing representations. The inhibition of competing representations in intentional memory has been little examined so far. In this study we attempt to analyze changes in activation in the recall of products on a shopping list and competitors through implicit memory tasks. Sixty-five participants learned two shopping lists on a computer. Later, they were told to virtually buy one of them (prospective list) and not the other (neutral list). Prior to intentional task execution, they performed an implicit retrieval task in which we manipulated the appearance or not of cues from the intentional list and analyzed the influence of the items from the intentional list on items related to intentional and neutral lists. The main result of this study is that intention retrieval by intentional cues strengthens the activation of products related to the intentional list and/or inhibits competing products related to the neutral list. The inhibition is episodic rather than semantic in nature. The ISE requires the recall of the intention during the retention period through intentional cues for maintaining the intention. This seems to defend automatic recovery theories and not the intention persistence hypothesis. Also, the results are better explained by the directed forgetting paradigm rather than by the retrieval-induced forgetting paradigm.     

Reversible Verbal Memory Integration Deficits in Obstructive Sleep Apnoea

When presented with novel but semantically related elements after learning verbal material, healthy participants tend to endorse these items as previously learned. This reflects the normal integration and association of novel verbal information into long-term memory. How obstructive sleep apnoea (OSA) negatively impacts verbal memory performance, and whether deficits are reversible following positive airway pressure (PAP) treatment, remain elusive. We investigated immediate and delayed OSA- and PAP treatment-related effects on verbal memory integration, using a false memory paradigm. Twenty-three patients with OSA learned lists of words semantically related to target non-presented words (1) at baseline after a polysomnography diagnosis night, (2) after a consecutive polysomnography night under PAP titration, and (3) after three months of compliant PAP treatment. At each session, participants learned 10 different lists of words, each list comprising 15 semantically related items. They had then to recognize 15 minutes later (after an intermediate vigilance task) previously learned words within a list including studied words (learned), unstudied but semantically related items (lures), and non-related unstudied items (controls). Sleep quality and fatigue questionnaires, and psychomotor vigilance tests (PVT) were administered at each session. PAP treatment led to OSA remission and improvement in objective and subjective sleep quality. Crucially, recognition of learned and lure words increased after the first night under treatment and remained stable three months later, suggesting successful memory integration and restoration of semantic processes. No treatment-related outcome was found on PVT performance. OSA exerts a detrimental but PAP-reversible effect on verbal learning and semantic memory integration mechanisms underlying the acquisition of novel memory representations.     

Semantic cuing and the scale insensitivity of recency and contiguity

In recalling a set of previously experienced events, people exhibit striking effects of recency, contiguity, and similarity: Recent items tend to be recalled best and first, and items that were studied in neighboring positions or that are similar to one another in some other way tend to evoke one another during recall. Effects of recency and contiguity have most often been investigated in tasks that require people to recall random word lists. Similarity effects have most often been studied in tasks that require people to recall categorized word lists. Here we examine recency and contiguity effects in lists composed of items drawn from 3 distinct taxonomic categories and in which items from a given category are temporally separated from one another by items from other categories, all of which are tested for recall. We find evidence for long-term recency and for long-range contiguity, bolstering support for temporally sensitive models of memory and highlighting the importance of understanding the interaction between temporal and semantic information during memory search.     

Going beyond a single list: Modeling the effects of prior experience on episodic free recall

We present an extension of the search of associative memory (SAM) model that simulates the effects of both prior semantic knowledge and prior episodic experience on episodic free recall. The model incorporates a memory store for preexisting semantic associations, a contextual drift mechanism, a memory search mechanism that uses both episodic and semantic associations, and a large lexicon including both words from prior lists and unpresented words. These features enabled the model to successfully account for the effects of prior semantic knowledge and prior episodic learning on the pattern of correct recalls and intrusions observed in free recall experiments.     

Selective deficits in episodic feeling of knowing in ageing: A novel use of the general knowledge task

Failure to recall an item from memory can be accompanied by the subjective experience that the item is known but currently unavailable for report. The feeling of knowing (FOK) task allows measurement of the predictive accuracy of this reflective judgement. Young and older adults were asked to provide answers to general knowledge questions both prior to and after learning, thus measuring both semantic and episodic memory for the items. FOK judgements were made at each stage for all unrecalled responses, providing a measure of predictive accuracy for semantic and episodic knowledge. Results demonstrated a selective effect of age on episodic FOK resolution, with older adults found to have impaired episodic FOK accuracy while semantic FOK accuracy remained intact. Although recall and recognition measures of episodic memory are equivalent between the two age groups, older adults may have been unable to access contextual details on which to base their FOK judgements. The results suggest that older adults are not able to accurately predict future recognition of unrecalled episodic information, and consequently may have difficulties in monitoring recently encoded memories.     

The fSAM model of false recall

The authors report a new theory of false memory building upon existing associative memory models and implemented in fSAM, the first fully specified quantitative model of false recall. Participants frequently intrude unstudied critical words while recalling lists comprising their strongest semantic associates but infrequently produce other extralist and prior-list intrusions. The authors developed the theory by simulating recall of such lists, using factorial combinations of semantic mechanisms operating at encoding, retrieval, or both stages. During encoding, unstudied words' associations to list context were strengthened in proportion to their strength of semantic association either to each studied word or to all co-rehearsed words. During retrieval, words received preference in proportion to their strength of semantic association to the most recently recalled single word or multiple words. The authors simulated all intrusion types and veridical recall for lists varying in semantic association strength among studied and critical words from the same and different lists. Multiplicative semantic encoding and retrieval mechanisms performed well in combination. Using such combined mechanisms, the authors also simulated several core findings from the Deese-Roediger-McDermott paradigm literature, including developmental patterns, specific list effects, association strength effects, and true-false correlations. These results challenge existing false-memory theories.     

Revelation without presentation: Counterfeit study list yields robust revelation effect

This study explores the revelation effect, a recognition memory phenomenon that occurs when test items (or related items) are specially processed before recognition judgment. These revealed items, whether targets or lures, receive a positive response bias. Although the effect occurs across various conditions, it has not been shown to occur when participants make judgments unrelated to episodic memory. We investigated whether the effect would occur when a recognition decision was nominally one of episodic memory, but when a complete episodic event had not occurred. Specifically, participants listened to noise that allegedly masked a list of words (in fact, no words existed). A revelation effect occurred with this pseudo-subliminal procedure, suggesting that the revelation effect need not rely on stimuli recalled through episodic memory but only a specific event to recall. The effect did not occur when participants simply guessed whether words were on an unheard list or made semantic judgments.