Inhibitory deficits in older adults: list-method directed forgetting revisited

Principal component analysis suggests multiple dimensions of memory inhibition that are differentially affected by age

Background

Cognitive inhibition is among the executive functions that decline early in the course of normal aging. Failures to be able to inhibit irrelevant information from memory may represent an essential factor of age-associated memory impairment. While a variety of elaborate behavioral tasks have been developed that presumably all index memory inhibition, the extent to which these different tasks measure the same underlying cognitive construct that declines with age has not been well explored.

Methods

In the current study, 100 and 75 cognitively healthy younger (n = 71; age = 30.7 ± 5.4 years, 56.7% female) and older (n = 104, age = 69.3 ± 5.9 years, 66.2% female) adults with equivalent educational attainment performed three computer-based memory inhibition tasks: the Retrieval Induced Forgetting task, the Suppress task, and the Directed Forgetting task. We conducted a principal component analysis using scores derived from different components of these tasks to explore whether and how the tasks relate to one another. We further investigated how age, sex and education, along with, in a subsample of the participants, a neuropsychological measure of episodic memory, impacted both the task scores individually, and the principal components derived from the exploratory analysis.

Results

We identified 3 distinct sources of variability which represent potentially independent cognitive processes: memory retrieval facilitation, and two memory inhibition processes that distinguished themselves by the degree of volitional initiation of memory suppression. Only the memory retrieval component correlated with a neuropsychologically-derived episodic memory score, and both memory inhibition principal components were age dependent.

Conclusion

Our findings provide support for a distinction in memory suppression processes between those 'instructed' to be performed and those which happen without explicit instruction. This distinction adds nuance to the dichotomous classification of controlled vs. automatic inhibitory mechanisms, which have been shown in previous work to vary as a function of the degree of frontal involvement. Our findings further demonstrate that while both of these measures of inhibition were affected by age, the episodic memory component was not, suggesting that inhibitory impairments may precede memory deficits in healthy aging.

Responsible Remembering and Forgetting in Younger and Older Adults

Although older adults are often concerned about instances of forgetting, forgetting can be a useful feature of our memory system. Specifically, strategically forgetting less important information can benefit memory for goal-relevant information (i.e., responsible remembering and responsible forgetting). In two experiments, we presented younger and older adults with a list of words (either unrelated words or items to bring on a camping trip) with a cue indicating whether participants ("You") or their "Friend" was responsible for remembering each item. Results revealed that both younger and older adults engaged in responsible remembering and forgetting by better remembering items they were responsible for remembering, indicating a strategic utilization of their limited memory capacity. Additionally, regardless of age and the cue indicating who was responsible for remembering each item, participants used importance to guide the encoding and retrieval of information. Thus, people may be able to engage strategic cognitive mechanisms to maximize memory utility for important, goal-relevant information, and responsible forgetting can enhance memory utility in both younger and older adults by using importance to drive memory and reduce consequences for forgetting.

Failing to forget? Evidence for both impaired and preserved working memory control in older adults

Voluntary forgetting is accomplished via top-down control over memory contents. Age-related declines in cognitive control may compromise voluntary forgetting. Using a working-memory variant of a directed forgetting task, we examined age differences in forgetting efficacy by analyzing direct measures of memory accuracy and two indirect measures of retention: proactive interference and semantic distortions. The directed forgetting effect in long-term memory was virtually absent in older adults. Further, compared to young adults, older adults recognized fewer to-be-remembered and more to-be-forgotten items in working memory. However, indirect measures of forgetting efficacy suggest some spared ability to control working memory contents in older adults: Both young and older adult participants exhibited reduced proactive interference for to-be-forgotten words (Experiment 1) and reduced semantic errors to to-be-forgotten list associates (Experiment 2) in working memory. Indirect memory measures of forgetting efficacy can provide a fuller understanding of spared and impaired control processes in older adults.

Does Amount of Pre-cue Encoding Modulate Selective List Method Directed Forgetting?

Prior work reported evidence that when people are presented with both a relatively short list of relevant information and a relatively short list of irrelevant information, a subsequent cue to forget the irrelevant list can induce successful selective directed forgetting of the irrelevant list without any forgetting of the relevant list. The goal of the present study is to determine whether this selectivity effect is restricted to short lists of information (six items per list), or if the effect generalizes to longer lists (12 items per list). In Experiment 1, we replicate the finding that selective directed forgetting can occur when short lists of relevant and irrelevant information are involved. Going beyond this replication, we show in Experiment 2 that such selectivity can arise both when shorter and when relatively long lists of items are used. The results are consistent with the view that selective directed forgetting can result from the action of a flexible inhibitory mechanism. They are less well in line with the view that selective cues to forget pre-cue information induce a change in participants' mental context.

Inhibitory Selection Mechanisms in Clinically Healthy Older and Younger Adults

Objective

Declines in working memory are a ubiquitous finding within the cognitive-aging literature. A unitary inhibitory selection mechanism that serves to guide attention toward task-relevant information and resolve interference from task-irrelevant information has been proposed to underlie such deficits. However, inhibition can occur at multiple time points in the memory-processing stream. Here, we tested whether the time point at which inhibition occurs in the memory-processing stream affects age-related memory decline.

Method

Clinically healthy younger (n = 23) and older (n = 22) adults performed two similar item-recognition working memory tasks. In one task, participants received an instruction cue telling them which words to attend to followed by a memory set, promoting perceptual inhibition at the time of encoding. In the other task, participants received the instruction cue after they received the memory set, fostering inhibition of items already in memory.

Results

We found that older and younger adults differed in their ability to inhibit items both during encoding and when items had to be inhibited in memory but that these age differences were exaggerated when irrelevant information had to be inhibited from memory. These results provide insights into the mechanisms that support cognitive changes to memory processes in healthy aging.

Intentional inhibition but not source memory is related to hallucination-proneness and intrusive thoughts in a university sample

Proneness to unusual perceptual states - such as auditory or visual hallucinations - has been proposed to exist on a continuum in the general population, but whether there is a cognitive basis for such a continuum remains unclear. Intentional cognitive inhibition (the ability to wilfully control thoughts and memories) is one mechanism that has been linked to auditory hallucination susceptibility, but most evidence to date has been drawn from clinical samples only. Moreover, such a link has yet to be demonstrated over and above relations to other cognitive skills (source monitoring) and cognitive states (intrusive thoughts) that often correlate with both inhibition and hallucinations. The present study deployed two tests of intentional inhibition ability - the Inhibition of Currently Irrelevant Memories (ICIM) task and Directed Forgetting (DF) task - and one test of source monitoring (a source memory task) to examine how cognitive task performance relates to self-reported i) auditory hallucination-proneness and ii) susceptibility to intrusive thoughts in a non-clinical student sample (N = 76). Hierarchical regression analyses were used to assess the independent and combined contributions of task performance to proneness scores. ICIM performance but not DF or source memory scores were significantly related to both hallucination-proneness and intrusive thoughts. Further analysis suggested that intrusive thoughts may mediate the link between intentional inhibition skills and auditory hallucination-proneness, suggesting a potential pathway from inhibition to perception via intrusions in cognition. The implications for studying cognitive mechanisms of hallucination and their role in "continuum" views of psychosis-like experiences are discussed.

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.

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.

The cognitive control of emotional versus value-based information in younger and older adults

We investigated age-related changes in the cognitive control of value-based and emotionally valenced information. In 2 experiments, participants completed a selectivity task in which to-be-recalled words differed in value and emotional salience. In Experiment 1, all low-valued words were emotional, and emotional valence (positive/negative) was manipulated between subjects. In Experiment 2, valence was manipulated within subjects, with the addition of a control condition in which all words (emotional and neutral) were equally valued. We found that older and younger adults recalled more neutral words than emotional words in both experiments when emotional words were low-valued, and more emotional words than neutral words in the control condition. Emotion did not interact with age in either experiment, suggesting that the impact of emotional saliency on memory is age-invariant. We also found that the number of items recalled was lower for older compared to younger adults in both experiments. Despite this, older and younger adults showed equivalent selectivity in terms of which words they recalled. These results suggest that older adults employ strategic control and use value-based information to guide memory processes equivalently to younger adults, even in the face of salient emotional information. (PsycINFO Database Record

No Inhibitory Deficit in Older Adults' Episodic Memory

Selectively retrieving a subset of previously studied material can cause forgetting of the unpracticed material. Such retrieval-induced forgetting is attributed to an inhibitory mechanism recruited to resolve interference among competing items. According to the inhibition-deficit hypothesis, older people experience a specific decline in inhibitory function and thus should show reduced retrieval-induced forgetting. However, the results of the two experiments reported here show the same amount of retrieval-induced forgetting in younger and older adults. These results indicate that retrieval inhibition is intact in older adults' episodic recall. The findings suggest that the common view of a general inhibitory deficit in older adults needs to be updated and that older adults show intact inhibition in some cognitive tasks and deficient inhibition in others.

Older adults can suppress unwanted memories when given an appropriate strategy

Memory suppression refers to the ability to exclude distracting memories from conscious awareness, and this ability can be assessed with the think/no-think paradigm. Recent research with older adults has provided evidence suggesting both intact and deficient memory suppression. The present studies seek to understand the conditions contributing to older adults' ability to suppress memories voluntarily. We report 2 experiments indicating that the specificity of the think/no-think task instructions contributes to older adults' suppression success: When older adults receive open-ended instructions that require them to develop a retrieval suppression strategy on their own, they show diminished memory suppression compared with younger adults. Conversely, when older adults receive focused instructions directing them to a strategy thought to better isolate inhibitory control, they show suppression-induced forgetting similar to that exhibited by younger adults. Younger adults demonstrate memory suppression regardless of the specificity of the instructions given, suggesting that the ability to select a successful suppression strategy spontaneously may be compromised in older adults. If so, this deficit may be associated with diminished control over unwanted memories in naturalistic settings if impeded strategy development reduces the successful deployment of inhibitory control.

Forgetting in context: the effects of age, emotion, and social factors on retrieval-induced forgetting

Retrieval-induced forgetting (RIF) refers to the finding that selectively retrieving some information impairs subsequent memory for related but nonretrieved information. This occurs both for the individual doing the remembering (i.e., within-individual retrieval-induced forgetting: WI-RIF), as well as for individuals merely listening to those recollections (i.e., socially shared retrieval-induced forgetting: SS-RIF). In the present study, we examined how the contextual factors of age and emotion independently and interactively affect both WI-RIF and SS-RIF. The results indicated that both WI-RIF and SS-RIF occurred at equivalent levels, both for younger and older adults and for neutral and emotional information. However, we identified a boundary condition to this effect: People only exhibited SS-RIF when the speaker that they were listening to was of the same sex as themselves. Given that participants reported feeling closer to same-sex speakers, this suggests that people co-retrieve more, and therefore exhibit increased SS-RIF, with close others. In everyday life, these RIF effects should influence what information is remembered versus forgotten in individual and collective memories.

Putting congeniality effects into context: Investigating the role of context in attitude memory using multiple paradigms

In three experiments, we evaluated remembering and intentional forgetting of attitude statements that were either congruent or incongruent with participants' own political attitudes. In Experiment 1, significant directed forgetting was obtained for incongruent statements, but not for congruent statements. In addition, in the remember group, recall was better for incongruent statements than congruent statements. To explain these findings, we propose a contextual competition at retrieval hypothesis, according to which incongruent statements become more strongly associated with their episodic context during encoding than do congruent statements. At the time of retrieval, incongruent statements compete with congruent statements due to the greater amount of contextual information stored in their memory trace. We tested this hypothesis in Experiment 2 by studying free recall of congruent and incongruent statements in a mixed-pure list design. In Experiment 3, memory for incongruent and congruent statements was tested under recognition test conditions that varied in terms of how much direct retrieval of contextual details they required. Overall, the results supported the contextual competition hypothesis, and they indicate the importance of context strength in both the remembering and intentional forgetting of attitude information.

Effects of emotion and age on performance during a think/no-think memory task

Recent studies have demonstrated that young adults can voluntarily suppress information from memory when directed to. After learning novel word pairings to criterion, participants are shown individual words and instructed either to "think" about the associated word, or to put it out of mind entirely ("no-think"). When given a surprise cued recall test, participants typically show impaired recall for no-think words relative to think or "control" (un-manipulated) words. The present study investigated whether this controlled suppression effect persists in an aged population, and examined how the emotionality of the to-be-suppressed word affects suppression ability. Data from four experiments using the think/no-think task demonstrate that older and younger adults can suppress information when directed to (Experiment 1), and the age groups do not differ significantly in this ability. Experiments 2 through 4 demonstrate that both age groups can suppress words that are emotional (positive or negative valence) or neutral. The suppression effect also persists even if participants are tested using independent probe words that are semantically related to the target words but were not the studied cue words (Experiments 3 and 4). These data suggest that the cognitive functioning necessary to suppress information from memory is present in older adulthood, and that both emotional and neutral information can be successfully suppressed from memory.

Are patients with obsessive-compulsive disorder generally more doubtful? Doubt is warranted!

A number of neuropsychological models implicate disinhibition and a lack of response confidence in the pathogenesis of obsessive-compulsive disorder (OCD). To provide a fair test of the inhibition and confidence account, a variant of the directed forgetting (DF) paradigm with OCD-related and unrelated conditions was administered in 30 OCD patients and 20 healthy controls. First, 16 words were presented which the participant was subsequently instructed to forget. Then, 16 words were presented that should be memorized. After a short interval, patients were shown the to-be-forgotten and the to-be-remembered items along with new items in random order. The subjects were instructed to recollect both the to-be-remembered and the to-be-forgotten items. The subject was asked to grade responses according to confidence. In accordance with prior findings from our group, patients did not differ from controls on overall recollection, response confidence, and the recollection of to-be-forgotten (allegedly inhibited) information. Our study cannot refute the claim that disinhibition plays a role in OCD in view of the vast array of paradigms tapping different aspects of inhibition. Still, we deem a psychological understanding more fruitful that looks at dysfunctional coping strategies and false beliefs as mechanisms for the persistence and pervasiveness of obsessive thoughts.

Aging and directed forgetting in episodic memory: A meta-analysis

In this meta-analysis, we examined the effects of aging on directed forgetting. A cue to forget is more effective in younger (d = 1.17) than in older (d = 0.81) adults. Directed-forgetting effects were larger (a) with the item method rather than with the list method, (b) with longer presentation times, (c) with longer postcue rehearsal times, (d) with single words rather than with verbal action phrases as stimuli, (e) with shorter lists, and (f) when recall rather than recognition was tested. Age effects were reliably larger when the item method was used, suggesting that these effects are mainly due to encoding differences.

Positive moods can eliminate intentional forgetting

People can intentionally forget previously studied information if, after study, a forget cue and new material to be encoded are provided. We examined how the affective state people experience during encoding of the new material modulates such directed forgetting. Positive, negative, and neutral moods were induced immediately before the new material was studied. The study materials themselves were neutral. The results showed sustained forgetting of the previously studied materials in negative moods but an elimination of the forgetting in positive moods. These findings agree with the effects of mood found for other cognitive tasks. They suggest that in positive moods, associative networks are activated, which leads to reactivation of List-1 items, and thus to elimination of the directed forgetting effects. These results contrast with recent reports on the role of emotional content in directed forgetting, which have described equivalent effects for neutral and emotional materials. Together, our findings suggest that directed forgetting is mainly affected by mood, and hardly at all by emotional content.

Inhibitory control of memory in normal ageing: dissociation between impaired intentional and preserved unintentional processes

The aim of this study was to compare the performance of elderly and young participants on a series of memory tasks involving either intentional or unintentional inhibitory control of memory content. Intentional inhibition processes in working and episodic memory were explored with directed forgetting tasks and in semantic memory with the Hayling task. Unintentional inhibitory processes in working memory, long-term memory, and semantic memory were explored with an interference resolution task, the retrieval practice paradigm, and the flanker task, respectively. The results indicate that elderly participants' performance on the two directed forgetting tasks and the Hayling task is lower than that of young ones, and that this impairment is not related to their initial memory capacity. This suggests that there is a specific dysfunction affecting intentional inhibitory control of memory contents in normal ageing.

The role of switching, inhibition and working memory in older adults' performance in the Wisconsin Card Sorting Test

The Wisconsin Card Sorting Test (WCST) is considered a typical executive test. However, several interesting questions are still open as to the specific executive processes underlying this task. In the present study, we explored how local and global switching, inhibition and working memory, assessed through the Number-Letter, the Stop Signal and the Reading Span tasks, relate to older adults' performance in the WCST. Results showed that older adults' performance variability in the number of perseverative errors was predicted by the local switch component of the Number-Letter task. Results also showed age-related differences in inhibition, working memory and global switching, while local switching resulted largely spared in aging. This study provides evidence that switching abilities may contribute to performance of older adults in the WCST. It also provides initial evidence suggesting that switching processes, associated with local switch costs, are involved in performance on the WCST, at least in older adults.

Oh, honey, I already forgot that: strategic control of directed forgetting in older and younger adults

Two experiments investigated list-method directed forgetting with older and younger adults. Using standard directed forgetting instructions, significant forgetting was obtained with younger but not older adults. However, in Experiment 1 older adults showed forgetting with an experimenter-provided strategy that induced a mental context change--specifically, engaging in diversionary thought. Experiment 2 showed that age-related differences in directed forgetting occurred because older adults were less likely than younger adults to initiate a strategy to attempt to forget. When the instructions were revised to downplay their concerns about memory, older adults engaged in effective forgetting strategies and showed significant directed forgetting comparable in magnitude to younger adults. The results highlight the importance of strategic processes in directed forgetting.