The benefits of item-method-directed forgetting

The present experiments examined the encoding and retrieval conditions in an item-method-directed forget (IMDF) study that included a novel control condition. In the IMDF condition, half of the items were followed by a remember cue whereas the other half were followed by a forget cue. In a remember-both control condition, half of the items were followed by an item identifier called Set A; whereas the other half of the items were followed by a Set B identifier. At the test, items were recalled as a function of the instruction cue or the set identifier. Across two experiments, directed-forgetting effects and associated benefits were found. Further, results from both studies revealed a new way to demonstrate the benefit of IMDF - directed-forgetting participants made more correct source attributions compared to remember-both participants. These benefits were obtained using a within-subjects IMDF paradigm (Experiment 1) as well as a between-subjects IMDF paradigm (Experiment 2). These patterns of results are consistent with several current theories of item-method-directed forgetting.

To-be-forgotten information shows more relative forgetting over time than to-be-remembered information

People can intentionally forget studied material when cued to do so. Corresponding evidence has arisen from studies on item-method directed forgetting, in which participants are asked to forget single items directly upon presentation. We measured memory performance of to-be-remembered (TBR) and to-be-forgotten (TBF) items across retention intervals of up to 1 week and fitted power functions of time to the observed recall (Experiment 1) and recognition (Experiment 2) rates. In both experiments and each retention interval condition, memory performance for the TBR items was higher than for the TBF items, supporting the view that directed forgetting effects are lasting. Recall and recognition rates of both TBR and TBF items were well fit by the power function. However, the relative forgetting rates of the two item types differed, with a higher forgetting rate for the TBF than the TBR items. The findings are consistent with the view that TBR and TBF items differ (mainly) in recruitment of rehearsal processes and resulting memory strength.

Drinking the waters of Lethe: Bringing voluntary choice into the study of voluntary forgetting

The directed forgetting paradigm has long been used to test whether humans can voluntarily choose to forget learned information. However, to date, nearly all directed forgetting paradigms have involved a forced-choice paradigm, in which the participants are instructed about which learned information they should forget. While studies have repeatedly shown that this directed forgetting does lead to a decreased ability to later remember the information, it is still unclear whether these effects would be present if participants were allowed to, of their own accord, choose which information they wanted to forget. In two experiments here, we introduce a free-choice variety of the item method directed forgetting paradigm and show that directed forgetting effects are robust, both for instructed and voluntary forgetting. We discuss the implications of our findings for notions of voluntary forgetting and for the self-choice effect in memory.

A computational account of item-based directed forgetting for nonwords: Incorporating orthographic representations in MINERVA 2

Recent research on item-method directed forgetting demonstrates that forget instructions not only decrease recognition for targets, but also decrease false recognition for foils from the same semantic categories as targets instructed to be forgotten. According to the selective rehearsal account of directed forgetting, this finding suggests that remember instructions may engage elaborative rehearsal of the category-level information of items. In contrast to this explanation, Reid and Jamieson (Canadian Journal of Experimental Psychology / Revue canadienne de psychologie expérimentale, 76(2), 75-86, 2022) proposed that the differential rates of false recognition may emerge at retrieval when foils from "remember" and "forget" categories are compared to traces in memory. Using MINERVA S, an instance model of memory based on MINERVA 2 that incorporates structured semantic representations, Reid and Jamieson successfully simulated lower false recognition for foils from "forget" categories without assuming rehearsal of category-level information. In this study, we extend the directed forgetting paradigm to categories consisting of orthographically related nonwords. Presumably participants would have difficulty rehearsing category-level information for these items because they would have no pre-experimental knowledge of these categories. To simulate the findings in MINERVA S, we imported structured orthographic representations rather than semantic representations. The model not only predicted differential rates of false recognition for foils from "remember" and "forget" categories, but also predicted higher rates of false recognition overall than what was observed for semantic categories. The empirical data closely matched these predictions. These data suggest that differential rates of false recognition due to remember and forget instructions emerge at retrieval when participants compare recognition probes to traces stored in memory.

Let me give you something to think about: Does needing to remember something new make it easier to forget something old?

In an item-method directed forgetting task, memory instructions presumably operate by promoting further rehearsal of to-be-remembered (TBR) items and limiting encoding of to-be-forgotten (TBF) items. We asked whether diverting attentional resources away from TBF items and towards a new item that needed to be committed to memory would improve forgetting. To this end, study words in our experiments were presented singly followed by a remember instruction (single-TBR), by a forget instruction (single-TBF), or else were replaced by a new word to be remembered (replace-TBR) in place of the original study word which could be forgotten (replace-TBF). A typical directed forgetting effect was observed across single and replace trials. However, there was no compelling evidence that forgetting was better for replace-TBF compared to single-TBF words, suggesting that, by itself, the explicit redirection of attentional and other processing resources away from forget items may not be sufficient to improve item-method directed forgetting.

Effects of emotion and sex difference on item-method directed forgetting

It is crucial to remember or forget others' faces in daily life. People can intentionally forget things they wish to forget, a phenomenon called directed forgetting (DF). This study examined the effects of stimuli's emotions and sex differences in participants and stimuli on DF. We used happy and angry faces as the items in a typical item-method paradigm and conducted three behavioral experiments. In Experiment 1, we recruited 60 participants to examine how emotions of stimuli and sex differences in participants and stimuli affected DF. In Experiment 2, we recruited 60 female participants and manipulated the durations of items presented during the study phase to examine whether the selective rehearsal theory was held. In Experiment 3, we recruited 50 female participants and attached recognition cues to the items presented during the test phase to examine whether the inhibitory control theory was held. We treated the sex of participants in Experiment 1, the durations of items presented during the study phase in Experiment 2 as the between-subject factors, and emotion and sex of stimuli as the with-subject factors. We conducted the mixed-design ANOVA for corrected hit rate, sensitivity, and bias based on the signal detection theory. As a result, we found that DF occurred easily for male participants, whereas not for female participants because of females' superior memorial performances and stronger sensitivities. Furthermore, we found that female participants owned the best and worst recognition rates for angry female faces and happy male faces, respectively. Our results supported the selective rehearsal theory, suggesting manipulations during the study phase had the potential to help females forget what they wished to forget. We presumed that psychologists and therapists should pay attention to the roles of sex difference in twofold, self and others, when studying people's memory and forgetting. Furthermore, the sensitivity of self and the emotion of others should be considered as well.

The effect of memory cue duration on performance in the directed forgetting task in healthy aging

Although forgetting is usually considered a memory error, intentional forgetting can function as an adaptive mechanism. The current study examined the effect of increased processing time on directed forgetting in aging as a mechanism to compensate for age-related forgetting. Specifically, an item-method directed forgetting paradigm was used in conjunction with Remember/Know/New responding to examine the effect of cue duration (1, 3, 5 s) on directed forgetting and remembering in younger and older adults. Results indicated that increased processing time improved performance in both age groups. Critically, older adults exhibited a linear increase in directed remembering performance across all cue durations which was related to individual differences in cognitive reserve. Specifically, those older adults with the highest levels of cognitive functioning showed the greatest memory benefit in the longest cue duration condition. These findings indicate the importance of processing time in accounting for intentional memory performance in older adults.

A functional near-infrared spectroscopy investigation of item-method directed forgetting

Whether directed forgetting is passive or active remains debated. Using functional near-infrared spectroscopy (fNIRS), blood-oxygen level-dependent responses of intentional forgetting were investigated in the item-method directed forgetting (DF) paradigm. During the study phase, each word was followed by a random remembering or forgetting cue indicating whether the word is to be remembered (TBR) or to be forgotten (TBF). A recognition test was used in the test phase and four cue-response conditions were obtained: remembering/forgetting cues associated with the subsequently remembered (TBR-r/TBF-r) or forgotten (TBR-f/TBF-f) words. Data from 16 healthy adult participants showed a DF effect. The fNIRS data revealed that, during the 5-9 s time window, the oxygenate hemoglobin (oxy-Hb) levels were higher during intentional forgetting compared to intentional remembering in the left inferior frontal (TBF-f vs. TBR-f) and right superior frontal gyrus (TBF-r vs. TBR-r), indicating more frontal inhibition involved during intentional forgetting. During the 9-11 s time window, the oxy-Hb level in the frontal and parietal gyrus was higher for forgetting than remembering cues, indicating that the TBF words might be automatically encoded. In sum, the TBF words might receive inhibition control triggered by forgetting cues and then be automatically encoded with the increase of the post-cue interval.

Training modulates memory-driven capture

Attention is captured by information matching the contents of working memory. Though many factors modulate the amount of capture, there is surprising resistance to cognitive control. Capture occurs even when participants are instructed either that an item would never be a target or to drop that item from memory. Does the persistence of capture under these conditions reflect a rigidity in capture, or can properly motivated participants learn to completely suppress distractors and/or completely drop items from memory? Surprisingly, no studies have looked at the influence of extensive training of involuntary capture from working memory items. Here, we addressed whether training leads to a reduction or even elimination of memory-driven capture. After memorizing a single object, participants were cued to remember or to forget this object. Subsequently, they were asked to execute a search task. To measure capture, we compared search performances in displays that did and did not contain a distractor matching the earlier memorized object. Participants completed multiple experimental sessions over four days. The results showed that attentional capture by to-be-remembered distractors was reduced, but not eliminated in subsequent sessions compared with the first session. Training did not impact capture by to-be-forgotten objects. The results suggest observable, but limited, cognitive control over memory-driven capture.

Selective remembering and directed forgetting are influenced by similar stimulus properties

Do the properties of to-be-remembered events influence the ability to remember, and also intentionally forget, these events in similar ways? Prior work has examined how the font size, animacy, emotionality, concreteness (the degree to which a word denotes something perceptible), frequency (how often a word appears in language), and length of to-be-remembered words influence memory. However, it was previously unclear whether the forgetting of information is also influenced by these characteristics. In six experiments, we used an item-method directed forgetting task where we presented participants with to-be-remembered and to-be-forgotten words varying in font size (large or small), animacy (animate or inanimate), emotionality (negative or neutral), concreteness (high or low), frequency (high or low), and word length (long or short). Results revealed that animacy, emotionality, concreteness, frequency, and word length (but not font size) influenced both remembering and forgetting. Together, the present findings indicate that the characteristics of presented words can influence remembering as well as directed forgetting, providing further evidence that the remembering and forgetting processes are governed by similar properties.

Instructions to shift eyes do not increase item-method directed forgetting

Successful forgetting of recently-studied information has been shown to be positively correlated with eye movements [Lee, Y. (2018). Withdrawal of spatial overt attention following intentional forgetting: Evidence from eye movements. Memory (Hove, England), 26(4), 503-513. https://doi.org/10.1080/09658211.2017.1378360]. We tested whether eye movements caused forgetting by manipulating instructions to move eyes following forget and remember cues in item-method directed forgetting. In Experiment 1, participants were instructed to move eyes to the periphery after TBF trials or to focus on the centre where the TBF word and cue had been presented. In Experiment 2, we manipulated eye movement instructions within participants such that on half of the TBR and TBF trials participants shifted their eyes to the periphery, and on the other half of the trials, participants focused on the centre of the screen. Experiment 3 replicated Experiment 2 with an added probe task which ensured participants were moving their eyes as instructed. Results overall showed eye movements did not increase directed forgetting. Instructing participants to shift or focus eyes did not interact with the effectiveness of directed forgetting. Furthermore, metacognitive measures collected during study indicated that participants are sensitive to the significant effects of directed forgetting, but - like recall - judgments were not affected by eye movement instructions. From these findings, we concluded that eye movements do not promote intentional forgetting.

Can intentional forgetting reduce the cross-race effect in memory?

Across three studies, we utilized an item-method directed forgetting (DF) procedure with faces of different races to investigate the magnitude of intentional forgetting of own-race versus other-race faces. All three experiments shared the same procedure but differed in the number of faces presented. Participants were presented with own-race and other-race faces, each followed by a remember or forget memory instruction, and subsequently received a recognition test for all studied faces. We obtained a robust cross-race effect (CRE) but did not find a DF effect in Experiment 1. Experiments 2 and 3 used shorter study and test lists and obtained a significant DF effect along with significant CRE, but no interaction between face type and memory instruction. The results suggest that own-race and other-race faces are equally susceptible to DF. The results are discussed in terms of the theoretical explanations for CRE and their implications for DF.

Developmental trajectories and brain correlates of directed forgetting in 22q11.2 deletion syndrome

22q11.2 deletion syndrome (22q11DS), also known as velo-cardio-facial syndrome (VCFS) is the most common copy number variant (CNV) in humans caused by a microdeletion on chromosome 22q11.2. The phenotype encompasses heart anomalies, cleft palate and cognitive difficulties. Alongside brain differences in VCFS, such as reduced hippocampal volume, different cognitive developmental trajectories can be observed. The aim of this study was to explore the developmental trajectories of cognitive inhibition in memory using longitudinal data acquired in a large cohort of individuals with 22q11DS and the brain correlates to those developmental changes. 51 participants with 22q11DS (mean age: 13.75 ± 4.26, mean IQ score: 70.50 ± 10.75) and 43 typically developing individuals matched for age (M = 13.50 ± 4.91) and gender were recruited. To explore inhibition in memory, the Directed Forgetting paradigm was used. 30 words were presented, half were 'To be remembered items'(TBR) and the other half 'To be forgotten items' (TBF). To measure source memory, participants were asked during the recognition stage to say if the world was a TBR or a TBF item. Participants were tested during two consecutive visits, with a mean interval of 3 years. T1-weighted images were acquired using a 1.5 T Philips or a 3 T Siemens scanner at both visits. Both groups recognized more TBR than TBF items (Directed forgetting effect), however, participants with 22q11DS recognized fewer TBR items and did not show an increased recognition of TBR items with age. Furthermore, in participants with VCFS increased source memory errors with age was associated with a decline in hippocampal volume.

The influence of cue probability on item and source judgments in item method directed forgetting

The current study examined how selective rehearsal strategies in item method directed forgetting are influenced by the probability of remember or forget cues from different sources. In four experiments, study words were presented by one of two sources in an item method directed forgetting paradigm. In all experiments, one source was mostly-remember (presenting twice as many remember as forget words) and the other source was mostly-forget (presenting twice as many forget as remember words). Participants completed item recognition tests (providing cue tags in Experiment 2) with source judgments. Item recognition of forget words was generally greater for the mostly-remember source than for the mostly forget source, whereas recognition of remember words was largely unaffected by source cue probability. Source judgments were consistent with heuristic guessing based on memory strength and knowledge of source cue probability. Experiment 4 analysed overt rehearsal, and showed that words from the mostly-remember source were more likely to be rehearsed prior to the memory cue. Results are discussed in terms of the influence that source cue probability knowledge has on selective rehearsal strategies, recognition decisions, and source memory attributions.

Separation of item and context in item-method directed forgetting

Contextual information plays a critical role in directed forgetting (DF) of lists of items, whereas DF of individual items has been primarily associated with item-level processing. This study was designed to investigate whether context processing also contributes to the forgetting of individual items. Participants first viewed a series of words, with task-irrelevant scene images (used as "context tags") interspersed between them. Later, these words reappeared without the scenes and were followed by an instruction to remember or forget that word. Multivariate pattern analyses of fMRI data revealed that the reactivation of context information associated with the studied words (i.e., scene-related activity) was greater whereas the item-related information diminished after a forget instruction compared to a remember instruction. Critically, we found the magnitude of the separation between item information and context information predicted successful forgetting. These results suggest that the unbinding of an item from its context may support the intention to forget, and more generally they establish that contextual processing indeed contributes to item-method DF.

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.

Refreshing and removing items in working memory: Different approaches to equivalent processes?

Researchers have investigated "refreshing" of items in working memory (WM) as a means of preserving them, while concurrently, other studies have examined "removal" of items from WM that are irrelevant. However, it is unclear whether refreshing and removal in WM truly represent different processes, or if participants, in an effort to avoid the to-be-removed items, simply refresh alternative items. We conducted two experiments to test whether these putative processes can be distinguished from one another. Participants were presented with sets of three words and then cued to either refresh one item or remove two items from WM, followed by a lexical decision probe containing either one of the just-seen words or a non-word. In Experiment 1, all probes were valid and in Experiment 2, probes were occasionally invalid (the probed word was one of the removed/non-refreshed items). In both experiments, participants also received a subsequent surprise long-term memory test. Results from both experiments suggested the expected advantages for refreshed (or non-removed) items in both short-term response time and long-term recognition, but no differences between refresh and remove instructions that would suggest a fundamental difference in processes. Thus, we argue that a functional distinction between refreshing and removal may not be necessary and propose that both of these putative processes could potentially be subsumed under an overarching conceptual perspective based on the flexible reallocation of mental or reflective attention.

Emotional devaluation in ignoring and forgetting as a function of adolescent development

We know that emotion and cognition interact to guide goal-directed behavior. Accordingly, it has recently been shown that distracting stimuli (Raymond, Fenske, & Tavassoli, 2003) and instructed to-be-forgotten items (Vivas, Marful, Panagiotidou, & Bajo, 2016) are emotionally devaluated. The devaluation by inhibition hypothesis (Raymond, Fenske, & Tavassoli, 2003) is the main theoretical explanation of these effects. However, we know little about how the cognition-emotion interplay is further modulated by development, and particularly, by changes in inhibitory control and affective processing within the adolescence period. In the present study we combined a selective attention task with faces, and a selective memory (directed forgetting paradigm) task with words, with a pleasantness evaluation task to address this question in three age groups; younger adolescents, older adolescents and young adults. Younger adolescents exhibited worse accuracy in the attention task, lower overall recognition of words in the memory task, and a smaller in magnitude directed forgetting effect in the latter, relative to the two older groups. That is, they showed less efficient inhibitory control in attention and memory selection. Despite this, all groups showed similar devaluation effects of the distractor faces and the to-be-forgotten words. Our findings do not fully support an inhibition account of such effects. Yet, they support the robustness of the forgetting devaluation effect, replicating the findings of Vivas, Marful, Panagiotidou, and Bajo (2016) with a Greek version of the task and in a bigger sample of participants.

Cognitive control of working memory but not familiarity in rhesus monkeys (Macaca mulatta)

Directed forgetting paradigms assess cognitive control by determining whether memory accuracy is superior in trials on which subjects were instructed to remember compared with accuracy in trials on which they were instructed to forget. We used a directed forgetting paradigm to compare the extent to which working memory and familiarity are subject to rehearsal-like cognitive control in rhesus monkeys. Monkeys studied a sample image, then saw one of two distinctive cues during a retention interval. The remember cue typically predicted a four-choice match to sample test, for which memory of the sample was critical. The forget cue typically predicted one of five perceptual discrimination tests, matched for accuracy to the memory tests, for which memory of the sample was irrelevant. On rare probe trials, the test type other than the type typically predicted by the cue was presented. When cognitive control of memory was possible, accuracy should have been higher on memory tests following the remember cue than on those following the forget cue. We found that accuracy was higher following the remember cue under conditions that favored working memory (small image set) but was not higher under conditions that favored matching on the basis of relative familiarity (large image set). Working memory, but not familiarity, is subject to cognitive control in rhesus monkeys.

Responsible remembering and forgetting as contributors to memory for important information

The ability to control both what we remember and what is forgotten can enhance memory. The present study used an item-method directed forgetting paradigm to investigate whether participants strategically remembered items they were responsible for remembering rather than items a hypothetical friend was responsible for remembering. Specifically, participants were presented with a 20-word list (either unrelated words or items to pack for a camping trip) with each word followed by a cue indicating whether the participant (You) or their "friend" (Friend) was responsible for remembering the word. When asked to recall all of the words, regardless of the cue, recall was sensitive to the You and Friend instructions such that participants demonstrated elevated recall for the items they were responsible for remembering, and participants also strategically organized retrieval by recalling You items before Friend items. Additionally, when asked to judge the importance of remembering each item, participants' recall and recognition were sensitive to item importance regardless of cue. Taken together, the present experiments revealed that the strategic encoding of important information and the forgetting of less important, goal-irrelevant information can maximize memory utility and minimize negative consequences for forgetting. Thus, we provide evidence for a metacognitive process we are calling responsible forgetting, where people attempt to forget less consequential information and focus on remembering what is most important.

ERP and behavioural measures of cognitive effort associated to forget negative and neutral words

The cognitive effort associated with remembering (R) vs forgetting (F) neutral and negative words was analyzed through a visual detection task integrated in an item-method directed forgetting task. Thirty-three younger adults participated in the experiment while their electrophysiological activity was registered in the study phase. The results shown: (1) negative words evoked more positive ERPs than neutral words on frontal regions, suggesting a preferential processing of negative words. (2) F-cues evoked more positive ERPs than R-cues did for neutral rather than negative words between 500 and 900 ms. This effect could reflect the difficulty in implementing inhibitory mechanisms on negative words. (3) At visual detection task, RTs for post-F probes were longer than for post-R probes. In 350-550 ms time window, ERPs were more positive for post-F probes than post-R probes in over right frontal regions and left medial parietal regions. Additionally, larger P2 were evoked by post-F negative probes than by post-R negative and post-F neutral ones. (4) In recognition test, participants recognized more negative TBF words than neutral ones. The ERP and behavioral results indicate that forgetting is more difficult than remembering, especially when words have a negative content, which implies a greater recruitment of parietal and frontal regions.

Wakefulness impairs selective consolidation of relevant trauma-associated memories resulting in more frequent intrusions

Recent studies show that sleep reduces intrusive memories after analog trauma. This effect is assumed to be caused by sleep's impact on memory consolidation. However, the underlying processes of this phenomenon have not been uncovered. Thus, the current study investigates the hypothesis that sleep reduces intrusive memories by supporting the selective consolidation of relevant memories. Seventy-five participants were exposed to traumatic picture stories before nocturnal sleep or wakefulness during daytime. Memory for relevant and irrelevant trauma-associated stimuli was assessed prior to and after the retention period. Consistent with the hypothesis, results demonstrate reduced memory loss for relevant as opposed to irrelevant trauma-associated stimuli after sleep but not after wakefulness. Moreover, an incremental retention benefit for relevant trauma-associated stimuli was negatively correlated with the number of intrusive trauma memories after wakefulness. These results suggest that lack of sleep impairs selective gating of relevant trauma-associated memories, thereby enhancing intrusion development after trauma.

Thought suppression inhibits the generalization of fear extinction

A challenge for translating fear extinction research into clinical treatments for stress and anxiety disorders is that extinction learning tends not to generalize beyond the treatment context. This may be because the hippocampus limits the expression of extinction memories. Consequently, downregulating the hippocampus may help to promote the generalization of extinction learning. One nonpharmacological strategy to downregulate hippocampal activity in humans is motivated forgetting, in which a participant deliberately attempts to suppress the encoding and/or retrieval of episodic memories. Here, we evaluated whether this strategy could facilitate extinction generalization by augmenting extinction training with thought suppression. Participants were threat conditioned using two conditioned stimulus (CS) categories paired with an electrical shock. Subsequently, during extinction training, one CS category was accompanied by thought suppression. Participants were tested for extinction generalization 24h later with conceptual variations of the extinguished stimuli. Contrary to our prediction, we found that extinction training paired with thought suppression resulted in enhanced shock expectancy (i.e., worse generalization) relative to standard extinction. We conclude that thought suppression during memory encoding likely acts as an inhibitory cue that blocks the acquisition of extinction memories, and therefore may not be a viable tactic to promote extinction generalization in the treatment of anxiety disorders.

What can directed forgetting tell us about clinical populations?

This paper reviews and critically assesses the implications of directed forgetting (DF) research on clinical populations. We begin by reviewing the typical methods and results of the item method and list method directed forgetting procedures and provide best practice recommendations for future studies using clinical populations. Next, we note that DF was often interpreted as being due to inhibition, and when clinical populations showed impaired directed forgetting, it was treated as evidence in inhibitory control difficulties. However, inhibition may not be the cause of DF effects, based on current understanding of these cognitive tasks. We instead suggest that item method DF is tied to attentional control, which might include inhibitory mechanisms (or might not). In contrast, list method DF is tied to two forms of memory control: control of mental context (indicated by effective forgetting of List 1), and changes in the strategies used to remember (indicated by better learning of List 2). We review the current state of the clinical DF literature, assess its strength based on our best practice recommendations, and call for more research when warranted.

Trust is essential: positive effects of information systems on users' memory require trust in the system

Initial results suggest that decision support systems (DSSs) can trigger 'directed forgetting' in business settings if users trust in the DSS. In the present study, we further examined this trust effect on DSS-cued forgetting and related positive effects on users' cognitive resources, performance, and well-being. Moreover, we investigated how trust translates into behavioural intentions to use a DSS, and into actual usage of the DSS. Finally, we examined if risk-related framing of decision outcomes (loss vs. gain framing) moderates trust effects on directed forgetting and behavioural intentions. In line with our expectations, results of an experiment with N = 200 participants confirmed that trust significantly enhances directed forgetting, performance, and well-being. Behavioural intentions fully mediated the trust effect on DSS use. Framing of decision outcomes showed no moderation but a main effect on directed forgetting, with loss framing reducing the directed forgetting effect. Practitioner summary: This experimental study demonstrates the importance of trust in information systems to leverage positive effects of these systems on users' cognitive resources, performance, and well-being in a simulated complex business setting. Abbreviations: DSS(s): decision support system(s); R-F: remember-forget difference; ANOVA: difference analysis of variance.

Directed forgetting of emotionally valenced faces

An item-method directed forgetting task was used in three studies to present photographs of happy, neutral and sad faces to participants who had been induced to adopt a happy, neutral or sad mood. At test remember, forget or new judgments of old and new photographs of happy, neutral or sad faces were collected. According to the affect-as-cognitive-feedback hypothesis positively valenced stimuli serve as 'go signals' validating the use of currently accessible cognitions to process task demands whereas negatively valenced stimuli serve as 'stop signals' inhibiting or reversing the use of those cognitions. Since directed forgetting tasks entail the cognitions (among others) that some stimuli should be remembered and others should be forgotten, happy faces should facilitate task demands whereas sad faces should not. As predicted, directed forgetting effects were found for happy but not sad faces in Experiments 1 and 3, and directed forgetting effects were found neutral valenced faces in Experiment 2. Across all three studies mood state did not influence directed forgetting. Findings are discussed in terms of the effects of facial valence cues on directed forgetting and some directions for future research.

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.

How do word frequency and memory task influence directed forgetting: An ERP study

In daily life, it is important either to remember sometimes or to intentionally forget on other occasions. The issue of forgetting following instructions (i.e. directed forgetting, DF) has been broadly studied; however, whether the frequency of contents would matter in DF remains unclear, and the understanding of its neural mechanism in both circumstances of item memory and source memory requires improvement in depth. For these purposes, the current study manipulated word frequency and memory task to investigate relevant behavioral features and neural activities of DF. Adopting event-related potential (ERP) technique, this study applied two-character Chinese words of two types of word frequency (high vs low) in the item-method DF paradigm. During encoding, we found that the increased frontal positivity, an index of active inhibition, was regulated by both word frequency and memory task, while the enhanced parietal positivity reflecting selective rehearsal didn't fluctuate across conditions. In the course of test, three ERP old/new effects were identified: the familiarity-based FN400 and the recollection-driven LPC were both modulated by word frequency and memory task, but the right frontal old/new effect was significant solely in source memory; also, these effects provided compelling evidence for the influences of word frequency and memory task on DF. Our results reinforce the differentiation between absolute familiarity and relative familiarity in memory, reveal their sensitivity to DF, and also support the dual-process interpretation. Implications are made to examine more influential factors for future research.

Forgetting cues are ineffective in promoting forgetting in the item-method directed forgetting paradigm

This study aims to investigate the effectiveness of forgetting cues in an item-method directed forgetting (DF) paradigm. A modified no-cue (NC) condition, in which participants could not adopt intentional forgetting strategy, was added to an item-method DF paradigm. Memory retention was compared between NC condition and to-be-forgotten (TBF) condition. The results revealed that the recognition reaction times (RTs) were shorter for the remembered TBF (TBF-R) words than for the remembered NC (NC-R) words, and were longer for the forgotten TBF words relative to the forgotten NC words, indicating that participants might be more familiar with the TBF words than the NC words. Event-related potential results showed that both LPC activity and frontal old/new effect were enhanced for TBF-R words relative to the NC-R words. These results might indicate that participants were more familiar with TBF words than NC words. This study further supports the view that forgetting cues may not in fact promote forgetting in the item-method DF paradigm.

The role of forgetting cues in directed forgetting: Ceasing maintenance rehearsal

The effect of forgetting cues on maintenance rehearsal in item-method directed forgetting (DF) paradigm was explored from behavioral and electrophysiological evidence. In Experiment 1, maintenance rehearsal was induced by a maintenance cue. Specifically, after the studied word, a maintenance (M) cue was presented before the presentation of a remembering/forgetting cue. When an M cue appeared, participants were required to wait for the following remembering (M-R) or forgetting (M-F) cue to determine whether the word needs to be remembered or not, and words were kept in short-term memory with maintenance rehearsal until the presentation of M-R/M-F cues. Four conditions were utilized: maintain-remembering (M-R), maintain-forgetting (M-F), maintenance (M), and forgetting (F). The results showed that, 1) superior recognition was found for the M-R relative to the M-F words, revealing a typical DF effect; 2) No recognition difference was found between M and M-F words, indicating that M-F cues showed little effect in promoting forgetting; 3) Inferior recognition was found for F than M words, indicating that the maintenance rehearsal might cease or be reduced by the presentation of F cues. In Experiment 2, event related potentials time-locked to cue (M-R, M-F, M, and F cues) onset during study phase. An enhanced fronto-central P3a component was evoked for F relative to M cues, indicating a more intensive attention orienting or attentional inhibition process triggered by F cues. These results demonstrated that forgetting cues might trigger an inhibition process to terminate the maintenance rehearsal process.

Not all information in visual working memory is forgotten equally

To improve maintenance of task-relevant information in visual working memory (VWM), previously encoded, but no longer relevant, information can be suppressed or forgotten. However, it is unclear whether a cue directing attention to a subset of stimuli leads to complete forgetting for non-cued stimuli. The current study utilized a novel method of testing to-be forgotten information to determine if the effectiveness of forgetting differs depending on the type of encoded stimuli. Participants performed a directed forgetting change detection task, and importantly, the changed stimulus could be a novel stimulus or a to-be-forgotten stimulus. Stimulus type (colors, objects, or shapes) was manipulated across two experiments. Results suggest that a cue benefits memory for to-be-remembered information, but performance is not equivalent to never encoding to-be-forgotten information. Furthermore, the type of encoded information impacts the extent of forgetting.

Directed forgetting in rats: Evidence for active memory control?

Directed forgetting in rats, to elucidate active control of memory rehearsal processes while controlling for nonmemorial artifacts, was examined using an eight-arm radial maze. To-be-remembered and to-be-forgotten items were presented at different arms in the same trial. A trial consisted of learning and test phases. Rats needed to remember win or loss of a food pellet presented in the middle of the arms, signaling presence or absence of a large reward there in the subsequent test phase. Two other qualitatively different foods placed at the end of the arms served as remember (R) or forget (F) cues, signaling whether those arms would be presented in the test phase. Compared with the normal test, rats' performance deteriorated significantly if the arms previously marked by F-cues in the preceding learning phase were actually used in the test phase, showing reliable directed forgetting in rats. Rats were also tested in a condition in which F-cues were not presented at all, and thus rats had to remember all the arms. Although positive evidence of reduction of memory load in working memory by utilizing F-cues was not demonstrated, analysis of individual data suggested that utilization of R-cues and F-cues interfered with the main task of remembering win/lose information.

Directed forgetting in organisations: the positive effects of decision support systems on mental resources and well-being

Decision makers in organisations are often overtaxed by huge amounts of information in daily business processes. As a potential support strategy, this study examined 'directed forgetting' (Bjork, 1970) in a simulated sales planning scenario. We assumed that the availability of a computer-based decision support system (DSS) triggers the forgetting of decision-related background information. Such directed forgetting should not only release memory capacities for additional tasks but also enhance decision quality and decrease strain of decision makers. Assumptions were tested in an experimental study with N = 90 participants. Consistent with our assumptions, results revealed a higher recall of decision-unrelated information, higher decision quality and higher well-being when participants could use a DSS as compared to two Control conditions without a DSS. Moreover, directed forgetting effects were qualified by participants' trust in the DSS. This study provides the first evidence for directed forgetting effects cued by information systems in a business context. Practitioner summary: Information overload is an increasing challenge in modern business organisations. Extending findings from basic memory research, this study shows that availability of a computer-based decision support system triggers forgetting of decision-related background information, which in turn increases users' mental resources for additional tasks, decision quality, and well-being.

Successful list-method directed forgetting without retroactive interference of post-instruction learning

The focus of the study is the role of interference in list-method directed forgetting. More specifically, our question was whether retroactive interference of the to-be-remembered information is a necessary prerequisite for the directed forgetting effect. In Experiment 1 we used a directed forgetting procedure with one learning list without the interference of any to-be-remembered information. In line with previous results, we did not find a significant directed forgetting effect. Experiment 2 applied a directed forgetting procedure with two study lists, however, the forget instruction was given following the second list. So, List 2 items were designated as to-be-forgotten items, without further learning, whereas List 1 items were to-be-remembered items. The forget instruction selectively decreased the recall of List 2 items, without decreasing the recall performance for List 1. In Experiment 3, using the same procedure with different items, smaller learning lists and reversed output order, we replicated the results of Experiment 2. Altogether, these results point to a flexible, goal-related nature of the directed forgetting phenomenon, showing that some form of interference is a necessary requirement for successful directed forgetting. However, proactive interference of to-be-remembered information in interaction with a forget instruction is suitable for forgetting of subsequently encoded information.

A grand memory for forgetting: Directed forgetting across contextual changes

Using an item-method directed forgetting task, we presented homographic homophonic nouns embedded in sentences. At study, each sentence was followed by an instruction to remember or forget the embedded word. On a subsequent yes-no recognition test, each word was again embedded within a sentence. In Experiments 1, 2, and 4 we varied the embedding sentence at test so that it was identical to that at study, changed but retained the meaning of the studied word, or changed to alter the meaning of the studied word. Repeated context - whether the sentence and/or the word meaning - proved to be as useful a retrieval cue for TBF items as for TBR items. In Experiment 3, we demonstrated that physical repetition was insufficient to produce context effects for either TBR or TBF items. And, in Experiment 4, we determined that participants were equally accurate in reporting context repetition/change following the correct recognition of TBR and TBF items. When considered in light of the existing literature, our results suggest that when context can be dissociated from the study item, it is encoded in "one shot" and not vulnerable to subsequent efforts to limit unwanted encoding.

Do different salience cues compete for dominance in memory over a daytime nap?

Information that is the most salient and important for future use is preferentially preserved through active processing during sleep. Emotional salience is a biologically adaptive cue that influences episodic memory processing through interactions between amygdalar and hippocampal activity. However, other cues that influence the importance of information, such as the explicit direction to remember or forget, interact with the inherent salience of information to determine its fate in memory. It is unknown how sleep-based processes selectively consolidate this complex information. The current study examined the development of memory for emotional and neutral information that was either cued to-be-remembered (TBR) or to-be-forgotten (TBF) across a daytime period including either napping or wakefulness. Baseline memory revealed dominance of the TBR cue, regardless of emotional salience. As anticipated, napping was found to preserve memory overall significantly better than remaining awake. Furthermore, we observed a trending interaction indicating that napping specifically enhanced the discrimination between the most salient information (negative TBR items) over other information. We found that memory for negative items was positively associated with the percentage of SWS obtained during a nap. Furthermore, the magnitude of the difference in memory between negative TBR items and negative TBF items increased with greater sleep spindle activity. Taken together, our results suggest that although the cue to actively remember or intentionally forget initially wins out, active processes during sleep facilitate the competition between salience cues to promote the most salient information in memory.

Motivated forgetting reduces veridical memories but slightly increases false memories in both young and healthy older people

The aim of the current study is to examine the effects of motivated forgetting and aging on true and false memory. Sixty young and 54 healthy older adults were instructed to study two lists of 18 words each. Each list was composed of three sets of six words associated with three non-presented critical words. After studying list 1, half of the participants received the instruction to forget List 1, whereas the other half received the instruction to remember List 1. Next, all the subjects studied list 2; finally, they were asked to remember the words studied in both lists. The results showed that when participants intended to forget the studied List 1, they were less likely to recall the studied words, but more likely to intrude the critical words. That is, we can intentionally forget something but this can also entail the intrusion of some related false memories.

Item-method directed forgetting: Effects at retrieval?

In an item-method directed forgetting paradigm, words are presented one at a time, each followed by an instruction to Remember or Forget; a directed forgetting effect is measured as better subsequent memory for Remember words than Forget words. The dominant view is that the directed forgetting effect arises during encoding due to selective rehearsal of Remember over Forget items. In three experiments we attempted to falsify a strong view that directed forgetting effects in recognition are due only to encoding mechanisms when an item method is used. Across 3 experiments we tested for retrieval-based processes by colour-coding the recognition test items. Black colour provided no information; green colour cued a potential Remember item; and, red colour cued a potential Forget item. Recognition cues were mixed within-blocks in Experiment 1 and between-blocks in Experiments 2 and 3; Experiment 3 added explicit feedback on the accuracy of the recognition decision. Although overall recognition improved with cuing when explicit test performance feedback was added in Experiment 3, in no case was the magnitude of the directed forgetting effect influenced by recognition cueing. Our results argue against a role for retrieval-based strategies that limit recognition of Forget items at test and posit a role for encoding intentions only.

Part-list cuing effects in children: A developmental dissociation between the detrimental and beneficial effect

Providing a subset of previously studied items as a retrieval cue can both impair and improve recall of the remaining items. Here, we investigated the development of these two opposing effects of such part-list cuing in children. Using listwise directed forgetting to manipulate study context access, three child age groups (7-8, 9-11, and 13-14years) and young adults studied a list of items and, after study, were asked to either forget or continue remembering the list. After presentation of a second list, participants were tested on predefined target items from the original list in either the presence or absence of the list's remaining (nontarget) items serving as retrieval cues. Results revealed that part-list cuing impaired recall of to-be-remembered target items regardless of age. In contrast, part-list cuing improved recall of to-be-forgotten target items in the adult and the oldest child groups but not in the two younger child groups. This finding suggests a developmental dissociation between the two opposing effects of part-list cuing, indicating that the beneficial effect develops later than the detrimental effect. In particular, following the view that the beneficial effect of part-list cuing arises from reactivation of the study context, the results suggest that elementary school children have difficulty in capitalizing on context reactivation.

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.

Effects of proactive interference on non-verbal working memory

Working memory (WM) is a cognitive system responsible for actively maintaining and processing relevant information and is central to successful cognition. A process critical to WM is the resolution of proactive interference (PI), which involves suppressing memory intrusions from prior memories that are no longer relevant. Most studies that have examined resistance to PI in a process-pure fashion used verbal material. By contrast, studies using non-verbal material are scarce, and it remains unclear whether the effect of PI is domain-general or whether it applies solely to the verbal domain. The aim of the present study was to examine the effect of PI in visual WM using both objects with high and low nameability. Using a Directed-Forgetting paradigm, we varied discriminability between WM items on two dimensions, one verbal (high-nameability vs. low-nameability objects) and one perceptual (colored vs. gray objects). As in previous studies using verbal material, effects of PI were found with object stimuli, even after controlling for verbal labels being used (i.e., low-nameability condition). We also found that the addition of distinctive features (color, verbal label) increased performance in rejecting intrusion probes, most likely through an increase in discriminability between content-context bindings in WM.

Forget Me if You Can: Attentional capture by to-Be-remembered and to-Be-forgotten visual stimuli

Previous studies on directed forgetting in visual working memory (VWM) have shown that, if people are cued to remember only a subset of the items currently held in VWM, they will completely forget the uncued, no longer relevant items. While this finding is indicative of selective remembering, it remains unclear whether directed forgetting can also occur in the absence of any concurrent to-be-remembered information. In the current study, we addressed this matter by asking participants to memorize a single object that could be followed by a cue to forget or remember this object. Following the cue, we assessed the object’s activation in VWM by determining whether a matching distractor would capture attention in a visual search task. The results showed that, compared to a cue to remember, a cue to forget led to a reduced likelihood of attentional capture by a matching distractor. In addition, we found that capture effects by to-be-remembered and to-be-forgotten distractors remained stable as the interval between the onset of the cue and the search task increased from 700 ms to 3900 ms. We conclude that, in the absence of any to-be-remembered objects, an instruction to forget an object held in WM leads to a rapid but incomplete deactivation of the representation of that object, thus allowing it to continue to produce a weak biasing effect on attentional selection for several seconds after the instruction to forget.

Directed forgetting of negative performed actions is difficult: A behavioural study

Strong evidence suggests that both performing actions and emotional stimuli can enhance memory by capturing attention. However, the synergetic effect of the two factors on directed forgetting has not been assessed. In this study, we used an item-method directed forgetting paradigm to examine the forgetting of emotional materials depending on whether actions were performed. The results showed that action performance influenced the directed forgetting of emotional words. Specifically, when actions were performed there was a directed forgetting effect for neutral and positive words but not for negative words. In comparison, for verbal tasks, directed forgetting was observed for all words. The elaborative encoding prior to the remember/forget instructions and the influence of negative emotion on attentional inhibition after the presentation of the instructions together suggest that it is more difficult to intentionally forget negative performed actions.

No evidence for age-related differences in item-method directed forgetting of emotional words

Research indicates that people can intentionally forget, but it is less clear how ageing and emotion interact with this ability. The present research investigated item-method directed forgetting of negative, neutral, and positive words in young (20-35 years), young-old (60-74 years), and old-old (75-89 years) adults. Although old-old adults showed overall reduced memory compared to young and young-old adults, all three age groups showed intentional forgetting. Moreover, intentional forgetting was not affected by the valence of the word in any of the three age groups. These findings suggest that younger and older adults can intentionally forget information that is neutral or emotional in nature. The present study's results extend previous research by showing that this ability is preserved in very old age.

A neural signature of contextually mediated intentional forgetting

The mental context in which we experience an event plays a fundamental role in how we organize our memories of an event (e.g. in relation to other events) and, in turn, how we retrieve those memories later. Because we use contextual representations to retrieve information pertaining to our past, processes that alter our representations of context can enhance or diminish our capacity to retrieve particular memories. We designed a functional magnetic resonance imaging (fMRI) experiment to test the hypothesis that people can intentionally forget previously experienced events by changing their mental representations of contextual information associated with those events. We had human participants study two lists of words, manipulating whether they were told to forget (or remember) the first list prior to studying the second list. We used pattern classifiers to track neural patterns that reflected contextual information associated with the first list and found that, consistent with the notion of contextual change, the activation of the first-list contextual representation was lower following a forget instruction than a remember instruction. Further, the magnitude of this neural signature of contextual change was negatively correlated with participants' abilities to later recall items from the first list.

Intending to forget is not easy: Behavioral and electrophysiological evidence

Previous researches have shown that recognition accuracy is lower for items cued to-be-forgotten (TBF) than to-be-remembered (TBR). Does directed forgetting help people forget more items than non-directed forgetting? Here, we modified the directed forgetting paradigm by adding a non-cue condition (NC). Consequently, non-directed forgetting would occur in NC. Behavioral results showed higher recognition accuracy for TBF than NC items, indicating that directed forgetting is less effective than non-directed forgetting. Electrophysiological results indicated that: (1) Remembered TBF items evoke an increased late positive component (LPC) than remembered NC items; (2) compared with remembered NC items, remembered TBF items showed a pronounced left-lateralized old/new effect and a reduced right-lateralized reversed old/new effect; (3) a right-lateralized reversed old/new effect was observed for forgotten TBF, but it was absent for forgotten NC items. These results demonstrate that the TBF items have a greater memory trace than the NC items. Forgetting cue has little effect of forgetting item from memory, and it might prompt subject to process or at least focus attention on the TBF items.

Abnormal brain activation during directed forgetting of negative memory in depressed patients

The frequent occurrence of uncontrollable negative thoughts and memories is a troubling aspect of depression. Thus, knowledge on the mechanism underlying intentional forgetting of these thoughts and memories is crucial to develop an effective emotion regulation strategy for depressed individuals. Behavioral studies have demonstrated that depressed participants cannot intentionally forget negative memories. However, the neural mechanism underlying this process remains unclear. In this study, participants completed the directed forgetting task in which they were instructed to remember or forget neutral or negative words. Standard univariate analysis based on the General Linear Model showed that the depressed participants have higher activation in the inferior frontal gyrus (IFG), superior frontal gyrus (SFG), superior parietal gyrus (SPG), and inferior temporal gyrus (ITG) than the healthy individuals. The results indicated that depressed participants recruited more frontal and parietal inhibitory control resources to inhibit the TBF items, but the attempt still failed because of negative bias. We also used the Support Vector Machine to perform multivariate pattern classification based on the brain activation during directed forgetting. The pattern of brain activity in directed forgetting of negative words allowed correct group classification with an overall accuracy of 75% (P=0.012). The brain regions which are critical for this discrimination showed abnormal activation when depressed participants were attempting to forget negative words. These results indicated that the abnormal neural circuitry when depressed individuals tried to forget the negative words might provide neurobiological markers for depression.

Memory suppression in Alzheimer's disease

An important challenge for memory is the competition between appropriate and inappropriate information during retrieval. This competition is normally reduced thanks to controlled inhibitory processes that suppress irrelevant memories. In Alzheimer's disease (AD), compromise of suppression ability may result in strong competition between relevant and irrelevant memories during retrieval. The present review highlights this issue by examining studies using the directed forgetting method in AD. This method in which participants are typically instructed to forget no longer relevant information is argued to reflect suppression in memory. Studies using the directed forgetting method suggest that AD participants experience difficulties when they are asked to suppress no longer relevant information in working, autobiographical, source and destination memory. Difficulties in suppressing irrelevant information, as may be observed in AD, may hamper memory retrieval by activating irrelevant memories at the expense of relevant ones.

Investigating biases of attention and memory for alcohol-related and negative words in alcohol-dependents with and without major depression after day-clinic treatment

This study aimed to investigate attentional and memory biases in alcohol-dependents with and without major depression compared to healthy controls. We assumed that both groups of alcohol-dependents would show attentional and memory biases for alcohol-related words. For the alcohol-dependents with depression, we additionally expected both types of biases for negative words. Alcohol-dependents without co-morbidity (Alc) and alcohol-dependents with major depression (D-Alc) as well as control participants with a moderate consumption of alcohol (Con) completed an alcohol Stroop task and a directed forgetting paradigm using word stimuli from three categories: neutral, negative, and alcohol-related. Stroop effects showed that not only alcohol-dependents but also control participants were more distracted by alcohol-related than by negative words. In the directed forgetting procedure, all participants showed a significant effect for each word-category, including alcohol-related and negative words. The D-Alc-group memorized more alcohol-related than negative to-be-remembered words. The results do not corroborate the hypothesis of more pronounced attentional and memory biases in alcohol-dependents. However, in alcohol-dependents with depression a memory bias for alcohol-related material was found, suggesting that this group may be more pre-occupied with alcohol than patients without such co-morbidity.