Selective memory retrieval can revive forgotten memories.

Humans remember less and less of what was encoded as more and more time passes. Selective retrieval can interrupt such time-dependent forgetting, enhancing recall not only of the retrieved but also of the nonretrieved information. The recall enhancement has been attributed to context retrieval and the idea that selective retrieval reactivates the retrieved item's temporal context during study, which can facilitate recall of other items that had a similar context at study. However, it is unclear whether context retrieval induces a transient discontinuity in the stream of temporal context only, or a more permanent updating of context that would entail a lasting interruption of time-dependent forgetting. In three experiments, we analyzed time-dependent forgetting of encoded information right after study and after time-lagged selective retrieval. Selective retrieval boosted recall of the nonretrieved information up to the levels observed directly after study. Intriguingly, it also created a restart of time-dependent forgetting that made forgetting after retrieval indistinguishable from forgetting after study and thus induced a reset of the recall process. The results suggest that selective retrieval can revive forgotten memories and cause lasting recall enhancement, effects likely mediated by context retrieval and a permanent updating of temporal context.

The role of mediators for the pretesting effect.

Taking a pretest (e.g., smoke - ?) before material is studied (smoke - fog) can improve later recall of that material, compared to material which was initially only studied. The goal of the present study was to evaluate for this pretesting effect the potential role of semantic mediators, i.e., of unstudied information that is semantically related to the study material. In all three experiments, subjects studied weakly associated word pairs (e.g., smoke - fog), half of which received a pretest. Subjects then either completed a recognition test (Experiment 1) or a cued-recall test (Experiments 2 and 3), during which they were presented with both the original study material and never-before-seen semantic mediators that were strongly related to the cue item of a pair (e.g., cigarette). Strikingly, presenting semantic mediators as lures led to higher false alarm rates for mediators following initial pretesting than study only (Experiment 1), and presenting semantic mediators as retrieval cues led to better recall of target items following pretesting than study only (Experiments 2 and 3). We argue that these findings support the elaboration account of the pretesting effect but are difficult to reconcile with other prominent accounts of the effect.

How retrieval practice and semantic generation affect subsequently studied material: an analysis of item-level effects.

The forward testing effect (FTE) refers to the finding that retrieval practice of previously studied material can facilitate recall of newly studied (critical) material. Such interim retrieval practice can also lead to a differential FTE, i.e., a more pronounced FTE for items at early than later serial positions in the critical material. The present study examined whether this differential FTE also holds with interim semantic generation of extra-list items, and whether it is influenced by study material. Consistent with prior work, the results of two experiments showed that both interim retrieval practice and interim semantic generation induce the general (list-level) FTE when unrelated study lists are applied, whereas retrieval practice only creates the effect with categorised study lists. Critically, however, the differential FTE was present in response to retrieval practice but absent in response to semantic generation. This pattern held regardless of which material was studied, thus experimentally dissociating the general (list-level) from the differential (item-level) FTE. The findings may suggest that retrieval practice, but not semantic generation, induces a reset of the encoding process which promotes attentional encoding such that a more pronounced FTE arises for early than middle and late serial positions in the critical list.

Item-method directed forgetting and perceived truth of news headlines.

Research on item-method directed forgetting (IMDF) suggests that memories can be voluntarily forgotten. IMDF is however usually examined with relatively simple study materials, such as single words or pictures. In the present study, we examined voluntary forgetting of news headlines from (presumably) untrustworthy sources. Experiment 1 found intact IMDF when to-be-forgotten headlines were characterised as untrustworthy and to-be-remembered headlines were characterised as trustworthy. Experiment 2 separated remember/forget cues and trustworthiness prompts. Forget cues alone had a large effect on memory, but only a small reducing effect on perceived truth. In contrast, trustworthiness prompts alone had essentially no effect on memory, but a large effect on perceived truth. Finally, Experiment 3 fully crossed forget/remember cues and trustworthiness prompts, revealing that forget cues can reduce memory irrespective of whether headlines are characterised as trustworthy or untrustworthy. Moreover, forget cues may bias source attributions, which can explain their small reducing effect on perceived truth. Overall, this work suggests that news headlines can be voluntarily forgotten. At least when people are motivated to forget information from untrustworthy sources, such forgetting may be helpful for curtailing the spread of false information.

The pretesting effect thrives in the presence of competing information.

Taking a pretest (e.g., blanket - ?) before some target material (blanket - sheet) is studied can promote recall of that material on a subsequent final test compared to material which was initially only studied. Here, we examine whether such pretesting can shield the tested material from interference-induced forgetting, which often occurs when before final testing, related material is encountered. We applied a typical pretesting task but asked subjects, between acquisition and final testing of the target list (list 1), to study two additional lists of items with either completely new and unique pairs (e.g., atom - cell) or overlapping - and thus potentially interfering - pairs (e.g., blanket - sleep). Target-list recall on the final test showed a typical pretesting effect for unique pairs, but the size of the effect even increased for overlapping pairs, as recall of study-only pairs was impaired, whereas recall of pretest pairs was left largely unaffected. This held regardless of whether a low (Experiment 1) or high (Experiment 2) degree of learning was induced for the interfering material, suggesting that pretesting can indeed protect the tested material from interference. These findings indicate that pretesting could play a significant role in educational settings where information often needs to be retained in the presence of competing information.

Retrieval practice reduces relative forgetting over time.

There is overwhelming evidence in the literature that retrieval practice of studied material can lead to better final recall than restudy of the same material. Far less clear is whether this recall benefit is accompanied by reduced subsequent forgetting over time. This study revisited the issue in two experiments by comparing the effects of retrieval practice - with and without feedback -, restudy, and a no-practice condition on recall across different delay intervals ranging between three minutes and several days. We fitted power functions of time to the recall rates of each practice condition and compared relative forgetting rates between conditions. The comparisons showed that relative forgetting was reduced after retrieval practice relative to restudy, the relative forgetting rate after retrieval practice was unaffected by the presence of feedback, and forgetting after restudy did not differ from the no-practice condition. Together with other findings in the literature, the results provide evidence that retrieval practice reduces relative forgetting over time.

List-method directed forgetting: Do critical findings generalize from short to long retention intervals?

People can purposefully forget information that has become irrelevant, as is demonstrated in list-method directed forgetting (LMDF). In this task, participants are cued to intentionally forget an already studied list (list 1) before encoding a second list (list 2); this induces forgetting of the first-list items. Most research on LMDF has been conducted with short retention intervals, but very recent studies indicate that such directed forgetting can be lasting. We examined in two experiments whether core findings in the LMDF literature generalize from short to long retention intervals. The focus of Experiment 1 was on the previous finding that, with short retention interval, list-2 encoding is necessary for list-1 forgetting to arise. Experiment 1 replicated the finding after a short delay of 3 min between study and test and extended it to a longer delay of 20 min. The focus of Experiment 1 was on the absence of list-1 forgetting in item recognition, previously observed after short retention interval. Experiment 1 replicated the finding after a short delay of 3 min between study and test and extended it to longer delays of 20 min and 24 h. Implications of the results for theoretical explanations of LMDF are discussed.

Category labels can influence the effects of selective retrieval on nonretrieved items.

Using lists of unrelated items as study material, recent studies have shown that selective retrieval of some studied items can impair or improve recall of the nonretrieved items, depending on whether the lag between study and selective retrieval is short or long. This study examined whether the results generalize when the items are studied together with their category labels (e.g., BIRD-magpie) and the category labels are reexposed as retrieval cues at test (e.g., BIRD-m___), a procedure often used in research on the effects of selective retrieval. Two lag conditions were employed in this study: a short 1-min lag between study and selective retrieval, and a longer 15-min lag that included mental context change tasks to enhance the lag-induced contextual drift. Experiment 1 employed lists of unrelated items in the absence of any category labels and replicated both the detrimental effect (after short lag) and the beneficial effect (after long lag) of selective retrieval. Experiment 1 was identical to Experiment 1 but provided the items' category labels during both study and retrieval, and Experiment 1 was identical to Experiment 1 but employed a categorized list. In both experiments, selective retrieval impaired recall in both lag conditions, indicating a critical role of category labels for the effects of selective retrieval. The results of the three experiments are consistent with a two-factor explanation of selective retrieval and the proposal that reexposure of category labels during retrieval can reinstate study context after longer lag.

Retrieval-induced forgetting in a social context: Do the same mechanisms underlie forgetting in speakers and listeners?

Selectively retrieving details from memory can result in forgetting related information, a finding known as retrieval-induced forgetting (RIF). The effect has mostly been examined in individuals, but RIF can also be socially transmitted and arise in listeners who are exposed to a speaker's selective memory retrieval. Whether within-individual RIF (WI-RIF) in speakers and socially shared RIF (SS-RIF) in listeners arise on the basis of the same cognitive mechanisms is unclear, however. In four experiments, we assessed both WI-RIF and SS-RIF while varying final test format to examine the potential involvement of output interference, strength-based blocking, and inhibition. WI-RIF and, to a similar degree, SS-RIF were observed on cued-recall tests with and without controlled output order at test, indicating that output interference cannot account for the observed forgetting. In contrast, SS-RIF was reduced relative to WI-RIF on tests of item recognition. These findings are consistent with the view that inhibition and blocking contribute to both WI-RIF and SS-RIF, but that the contribution of inhibition is reduced in listeners relative to speakers.

Selective directed forgetting in children.

When, after study of an item list, adults are cued to forget some of the list items and encode new information instead, such cuing often induces selective forgetting of the to-be-forgotten material without impairing recall of the other items. This study examined developmental trends in such selective directed forgetting by having second graders, sixth graders, and young adults study three successive lists of items and, after study of List 2, cuing them either to remember both List 1 and List 2 or to forget List 2 but remember List 1. Consistent with prior work, second graders exhibited no forgetting at all in response to the forget cue, whereas young adults selectively forgot List 2. Sixth graders showed still another pattern with forgetting of both List 1 and List 2, suggesting that the ability to selectively forget is still absent at this age level. Directed forgetting has often been attributed to the action of inhibitory control processes. On the basis of this view, the current finding that children during middle childhood do not yet show selective forgetting indicates that the control processes underlying selective directed forgetting mature into adolescence and early adulthood.

Hypermnesia and the Role of Delay between Study and Test.

Hypermnesia is increased recall across repeated tests in the absence of any further study opportunities. Although over the years many factors have been identified that influence hypermnesia, to date not much is known about the role of delay between study and test for the effect. This study addressed the issue in four experiments. Employing both words and pictures as study material, we compared hypermnesia after shorter delay (3 min or 11.5 min) and longer delay (24 h or 1 week) between study and test. Recall occurred over three successive tests, using both free recall (Experiments 1, 2, and 4) and forced recall testing (Experiment 3). In forced recall tests, subjects are instructed to recall as many items as possible, but if unable to remember all studied items, to fill in the remaining spaces with their best guesses. With free recall testing, hypermnesia increased with delay and the effect was driven mainly by reduced item losses between tests. These results suggest a link between hypermnesia and the testing effect, which shows that demanding retrieval practice, as it happens after longer delay, can improve recall by reducing the forgetting of the practiced items. In contrast, with forced recall testing, hypermnesia decreased with delay and was even absent after longer delay. The findings indicate that recall format can influence hypermnesia and different mechanisms may mediate the effects of repeated testing in the two recall conditions.

Sex, age, and sex hormones affect recall of words in a directed forgetting paradigm.

During the course of serious discussion, an unexpected interruption may induce forgetting of the original topic of a conversation. Sex, age, and sex hormone levels may affect frequency and extension of forgetting. In a list-method directed forgetting paradigm, subjects have to learn two word lists. After learning list 1, subjects receive either a forget or a remember list 1 cue. When the participants had learned list 2 and completed a distraction task, they were asked to write down as many recalled items as possible, starting either with list 1 or list 2 items. In the present study, 96 naturally cycling women, 60 oral contraceptive users, 56 postmenopausal women, and 41 young men were assigned to one of these different experimental conditions. Forget-cued young subjects recall fewer list 1 items (list 1 forgetting) but more list 2 items (list 2 enhancement) compared with remember-cued subjects. However, forget-cued postmenopausal women showed reduced list 1 forgetting but enhanced list 2 retention. Remember-cued naturally cycling women recalled more list 1 items than oral contraceptive users, young men, and postmenopausal women. In forget-cued follicular women, salivary progesterone correlated positively with recalled list 2 items. Salivary 17ß-estradiol did not correlate with recalled list 1 or list 2 items in either remember- or forget-cued young women. However, salivary 17ß-estradiol correlated with item recall in remember-cued postmenopausal women. Our findings suggest that sex hormones do not globally modulate verbal memory or forgetting, but selectively affect cue-specific processing. © 2016 Wiley Periodicals, Inc.

Collaborative remembering revisited: Study context access modulates collaborative inhibition and later benefits for individual memory.

Collaborating groups typically show reduced recall relative to nominal groups, i.e., to the cumulated non-redundant recall of the same number of people remembering in isolation-a finding termed collaborative inhibition. Motivated by the results of several previous studies, this study examined in two experiments whether access to study context at test influences the effects of collaboration. In both experiments, subjects collaborated in triads or recalled previously studied material in isolation. Experiment 1 applied short versus prolonged retention intervals to vary access to study context at test, whereas Experiment 2 used the list-method directed forgetting task and applied remember versus forget instructions to modulate context access. In both experiments, collaborative inhibition was present when access to study context at test was intact (i.e., after the short delay and the remember instruction) but was eliminated when the access was impaired (i.e., after the prolonged delay and the forget instruction). Also, post-collaborative gains for individual recall were greater when context access was impaired and collaborative inhibition was eliminated. The findings demonstrate a critical role of access to study context at test for collaborative inhibition, indicating that impaired context access may reflect a general boundary condition for the recall impairment. The possible role of context reactivation processes for beneficial effects of social recall is discussed.

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.

Reversing the testing effect by feedback: Behavioral and electrophysiological evidence.

The testing effect refers to the finding that retrieval practice of previously studied information enhances its long-term retention more than restudy practice does. Recent work showed that the testing effect can be dramatically reversed when feedback is provided to participants during final recall testing (Storm, Friedman, Murayama, & Bjork, 2014). Following this prior work, in this study, we examined the reversal of the testing effect by investigating oscillatory brain activity during final recall testing. Twenty-six healthy participants learned cue-target word pairs and underwent a practice phase in which half of the items were retrieval practiced and half were restudy practiced. Two days later, two cued recall tests were administered, and immediate feedback was provided to participants in Test 1. Behavioral results replicated the prior work by showing a testing effect in Test 1, but a reversed testing effect in Test 2. Extending the prior work, EEG results revealed a feedback-related effect in alpha/lower-beta and retrieval-related effects in slow and fast theta power, with practice condition modulating the fast theta power effect for items that were not recalled in Test 1. The results indicate that the reversed testing effect can arise without differential strengthening of restudied and retrieval-practiced items via feedback learning. Theoretical implications of the findings, in particular with respect to the distribution-based bifurcation model of testing effects (Kornell, Bjork, & Garcia, 2011), are discussed.

Testing enhances subsequent learning in older but not in younger elementary school children.

In adults, testing can enhance subsequent learning by reducing interference from the tested information. Here, we examined this forward effect of testing in children. Younger and older elementary school children and adult controls studied four lists of items in anticipation of a final cumulative recall test. Following presentation of each of the first three lists, participants were immediately tested on the respective list, or the list was re-presented for additional study. Results revealed that, compared to additional study, immediate testing of Lists 1-3 enhanced memory for the subsequently studied List 4 in adults and older elementary school children, but not in younger elementary school children. The findings indicate that the forward effect of testing is a relatively late-maturing phenomenon that develops over middle childhood and is still inefficient in the early elementary school years. Together with the results of other recent studies, these findings point to a more general problem in young children in combating interference.

Brain Oscillations Mediate Successful Suppression of Unwanted Memories.

To avoid thinking of unwanted memories can be a successful strategy to forget. Studying brain oscillations as measures of local and inter-regional processing, we shed light on the neural dynamics underlying memory suppression. Employing the think/no-think paradigm, 24 healthy human subjects repeatedly retrieved (think condition) or avoided thinking of (no-think condition) a previously learned target memory upon being presented with a reminder stimulus. Think and no-think instructions were delivered by means of a precue that preceded the reminder by 1 s. This allowed us to segregate neural control mechanisms that were triggered by the precue from the effect of suppression on target memory networks after presentation of the reminder. Control effects were reflected in increased power in the theta (5-9 Hz) frequency band in the medial and dorsolateral prefrontal cortex and higher long-range alpha (10-14 Hz) phase synchronization. Successful suppression of target memories was reflected in a decrease of theta oscillatory power in the medial temporal lobes and reduced long-range theta phase synchronization emerged after presentation of the reminder. Our results suggest that intentional memory suppression correlates with increased neural communication in cognitive control networks that act in down-regulating local and inter-regional processing related to memory retrieval.

Retrieval practice can eliminate list method directed forgetting.

It has recently been shown that retrieval practice can reduce memories' susceptibility to interference, like retroactive and proactive interference. In this study, we therefore examined whether retrieval practice can also reduce list method directed forgetting, a form of intentional forgetting that presupposes interference. In each of two experiments, subjects successively studied two lists of items. After studying each single list, subjects restudied the list items to enhance learning, or they were asked to recall the items. Following restudy or retrieval practice of list 1 items, subjects were cued to either forget the list or remember it for an upcoming final test. Experiment 1 employed a free-recall and Experiment 1 a cued-recall procedure on the final memory test. In both experiments, directed forgetting was present in the restudy condition but was absent in the retrieval-practice condition, indicating that retrieval practice can reduce or even eliminate this form of forgetting. The results are consistent with the view that retrieval practice enhances list segregation processes. Such processes may reduce interference between lists and thus reduce directed forgetting.

List-method directed forgetting: Evidence for the reset-of-encoding hypothesis employing item-recognition testing.

In list-method directed forgetting (LMDF), people are cued to forget a previously studied item list (List 1) and to learn a new list of items (List 2) instead. Such cuing typically enhances memory for the List 2 items, in both recall and (sometimes) item-recognition testing. It has recently been hypothesized that the enhancement effect for List 2 items (partly) reflects the result of a reset-of-encoding process. The proposal is that encoding efficacy decreases with an increase in study material, but the forget cue can reset the encoding process to make the encoding of early List 2 items as effective as the encoding of early List 1 items. An experiment is reported that examined the reset-of-encoding hypothesis with item-recognition testing, examining influences of items' serial learning position on the effects of the forget cue. Item-recognition tests were conducted separately for the two lists. Consistent with the reset-of-encoding hypothesis, the results showed strong enhancement effects for early List 2 items, but hardly any enhancement effects for middle and late List 2 items. Like in previous item-recognition studies, no cuing effects were found for List 1 items. The results support two-mechanism accounts of LMDF, which assume a critical role for a reset-of-encoding process for List 2 enhancement.

Working memory capacity predicts the beneficial effect of selective memory retrieval.

Selective retrieval of some studied items can both impair and improve recall of the other items. This study examined the role of working memory capacity (WMC) for the two effects of memory retrieval. Participants studied an item list consisting of predefined target and nontarget items. After study of the list, half of the participants performed an imagination task supposed to induce a change in mental context, whereas the other half performed a counting task which does not induce such context change. Following presentation of a second list, memory for the original list's target items was tested, either with or without preceding retrieval of the list's nontarget items. Consistent with previous work, preceding nontarget retrieval impaired target recall in the absence of the context change, but improved target recall in its presence. In particular, there was a positive relationship between WMC and the beneficial, but not the detrimental effect of memory retrieval. On the basis of the view that the beneficial effect of memory retrieval reflects context-reactivation processes, the results indicate that individuals with higher WMC are better able to capitalise on retrieval-induced context reactivation than individuals with lower WMC.