Implicit Memory Tests Research Articles

Some young adults hyper-bind too: Attentional control relates to individual differences in hyper-binding.

Hyper-binding - the erroneous encoding of target and distractor information into associative pairs in memory - has been described as a unique age effect caused by declines in attentional control. Previous work has found that, on average, young adults do not hyper-bind. However, if hyper-binding is caused by reduced attentional control, then young adults with poor attention regulation should also show evidence of hyper-binding. We tested this question with an individual differences approach, using a battery of attentional control tasks and relating this to individual differences in hyper-binding. Participants (N = 121) completed an implicit associative memory test measuring memory for both target-distractor (i.e., hyper-binding) and target-target pairs, followed by a series of tasks measuring attentional control. Our results show that on average, young adults do not hyper-bind, but as predicted, those with poor attentional control show a larger hyper-binding effect than those with good attentional control. Exploratory analyses also suggest that individual differences in attentional control relate to susceptibility to interference at retrieval. These results support the hypothesis that hyper-binding in older adults is due to age-related declines in attentional control, and demonstrate that hyper-binding may be an issue for any individual with poor attentional control, regardless of age.

Alterations in whole-brain dynamic functional stability during memory tasks under dexmedetomidine sedation.

This study aimed to explore the neurological effects of dexmedetomidine-induced sedation on memory using functional stability, a whole-brain voxel-wise dynamic functional connectivity approach. A total of 16 participants (10 men) underwent auditory memory task-related fMRI in the awake state and under dexmedetomidine sedation. Explicit and implicit memory tests were conducted 4 h after ceasing dexmedetomidine administration. One-sample Wilcoxon signed rank test was applied to determine the formation of explicit and implicit memory in the two states. Functional stability was calculated and compared voxel-wise between the awake and sedated states. The association between functional stability and memory performance was also assessed. In the awake baseline tests, explicit and implicit memory scores were significantly different from zero (p < 0.05). In the tests under sedation, explicit and implicit memory scores were not significantly different from zero. Compared to that at wakeful baseline, functional stability during light sedation was reduced in the medial prefrontal cortex, left angular gyrus, and right hippocampus (all clusters, p < 0.05, GRF-corrected), whereas the left superior temporal gyrus exhibited higher functional stability (cluster p < 0.05, GRF-corrected). No significant associations were observed between functional stability and memory test scores. The distribution and patterns of alterations in functional stability during sedation illustrate the modulation of functional architecture by dexmedetomidine from a dynamic perspective. Our findings provide novel insight into the dynamic brain functional networks underlying consciousness and memory in humans.

Attention and Memory in Depersonalization-Spectrum Dissociative Disorders: Impact of Selective-Divided Attentional Condition, Stimulus Emotionality, and Stress

ABSTRACT We investigated cognition in depersonalization-spectrum dissociative disorders without comorbid posttraumatic stress disorder to explore evidence for emotionally avoidant information processing. Forty-eight participants with DSM-IV dissociative disorder (DD) (Depersonalization Disorder – 37, Dissociative Disorder NOS −11), 36 participants with Posttraumatic Stress Disorder (PTSD), and 56 healthy controls (HC) were administered the Weschler Adult Intelligence Scale-III (WAIS); the Weschler Memory Scale-III (WMS); and three Stroop tasks: the Standard Stroop, a selective-attention Emotional Stroop using neutral, dissociation, and trauma-related word categories, and a divided-attention Emotional Stroop using comparable words. Participants were also administered a paired-associates explicit and implicit memory test using emotionally neutral and negative words, before and after the Trier Social Stress Test. The DD and HC groups had comparable general intelligence and memory scores, though dissociation severity was inversely related to verbal comprehension and working memory. In the selective-attention condition, DD participants showed greater incidental recall across word categories with comparable interference. However in the divided-attention condition, DD participants significantly favored lesser attentional interference at the expense of remembering words. Across attentional conditions, DD participants had better recall for disorder-related than neutral words. Pre-stress, the DD group demonstrated better explicit memory for neutral versus negative words with reversal after stress, whereas the HC group demonstrated the opposite pattern; implicit memory did not differ. Cognition in the PTSD control group was generally dissimilar to the DD group. The findings in toto provide substantial evidence for emotionally avoidant information processing in DD, vulnerable to the impact of stress, at the level of both attention and memory.

Sleep-learning impairs subsequent awake-learning

Although we can learn new information while asleep, we usually cannot consciously remember the sleep-formed memories – presumably because learning occurred in an unconscious state. Here, we ask whether sleep-learning expedites the subsequent awake-learning of the same information. To answer this question, we reanalyzed data (Züst et al., 2019, Curr Biol) from napping participants, who learned new semantic associations between pseudowords and translation-words (guga–ship) while in slow-wave sleep. They retrieved sleep-formed associations unconsciously on an implicit memory test following awakening. Then, participants took five runs of paired-associative learning to probe carry-over effects of sleep-learning on awake-learning. Surprisingly, sleep-learning diminished awake-learning when participants learned semantic associations that were congruent to sleep-learned associations (guga-boat). Yet, learning associations that conflicted with sleep-learned associations (guga-coin) was unimpaired relative to learning new associations (resun-table; baseline). We speculate that the impeded wake-learning originated in a deficient synaptic downscaling and resulting synaptic saturation in neurons that were activated during both sleep-learning and awake-learning.

Can’t forget: disruption of the right prefrontal cortex impairs voluntary forgetting in a recognition test

ABSTRACTThe causal influence of the dorsolateral prefrontal cortex (DLPFC) in voluntary forgetting remains unclear. Here, we employed repetitive transcranial magnetic stimulation (rTMS) over the right DLPFC to temporarily disrupt function of this brain region and examined its influence on an item-method directed forgetting (DF) task with both neutral and negative emotional memories. Participants were assigned to either an active or a sham rTMS group, in which we administered stimulation for 20 min before the DF task. We then examined the explicit and implicit DF effects with an explicit recognition and an implicit word completion test. We found that while participants in the sham group showed the classic DF effects in both explicit and implicit memory tests, temporally disrupting activity of the right DLPFC selectively reduced the DF effect on explicit recognition, but not on implicit word completion test. Our findings provide novel evidence that the right DLPFC plays a causal role in voluntary forgetting and support the direct inhibition account of voluntary memory control. Intriguingly, preserved implicit DF effects in the active stimulation group suggest that unintentional expressions of unwanted memories may be more sensitive to DF and less dependent on the right DLPFC.

Differential effects of sleep on explicit and implicit memory for potential trauma reminders: findings from an analogue study

ABSTRACT Background: Recent findings suggest that disruptions of sleep-related memory processing are involved in the development of posttraumatic stress symptoms. More specifically, exposure to an analogue traumatic event resulted in fewer intrusive memories, when it was followed by sleep instead of continued wakefulness. However, competing evidence suggests that sleep deprivation may reduce intrusive re-experiencing. To address these conflicting accounts, we examined how sleep – as opposed to partial sleep deprivation – modulates explicit and implicit trauma memory using an analogue procedure. Methods: Healthy participants (N = 41) were assigned to a Sleep or Partial sleep deprivation group. Prior to nocturnal sleep, both groups were exposed to “traumatic“ picture stories. After sleep or partial sleep deprivation, participants were subjected to tests of explicit and implicit memory for potential trauma reminders. Thereafter, participants completed an intrusion triggering task that was embedded in a distractor task. Results: Analyses revealed higher explicit memory for potential trauma reminders after sleep as compared to partial sleep deprivation. No group differences were found for implicit memory. Participants responded with fewer intrusions after sleep than following partial sleep deprivation. Conclusions: The current findings support a protective role of sleep in trauma memory processing, which may be evident after the first night of sleep post-trauma. Although more research is needed, our results corroborate the importance of promoting restful sleep in trauma-exposed individuals.

An Investigation of Sex Differences, Implicit Memory, and Perceptual Identification in the Survival Memory Paradigm

Robust support has been found for a survival processing effect on memory when information is encoded for its fitness relevance (Nairne et al. J Exp Psychol Learn Mem Cogn 33:263–273, 2007). However, support for this effect has been limited to forms of memory that require intentional, explicit retrieval processes. Thus far, the literature has failed to identify the effect in implicit, automatic memory using conceptual and perceptual production tasks (McBride et al. Mem Cogn 41:862–871, 2013; Tse and Altarriba Mem Cogn 38:1110–1121, 2010). In the current study, an alternative implicit memory test that employs different memory processes was employed in a further attempt to examine the survival processing effect in implicit memory. Participants rated a list of unrelated nouns according to their relevance to either a grassland survival or home-moving scenario in a within-subjects (Experiment 1a) or a between-subjects (Experiment 1b) design. A perceptual identification task was then completed in which accuracy and response times were recorded for the identification of occluded words previously rated in the survival context, moving context, or novel words. Overall, there was no response difference across participants in the implicit or explicit conditions. However, a significant interaction between rating scenario and sex was found in Experiment 1a, suggesting that males and females differentially identify occluded words studied from an evolutionarily relevant perspective. Implications of these results for the survival processing advantage are discussed.

Implicit Vocabulary Learning during Sleep Is Bound to Slow-Wave Peaks

Learning while asleep is a dream of mankind, but is often deemed impossible because sleep lacks the conscious awareness and neurochemical milieu thought to be necessary for learning. Current evidence for sleep learning in humans is inconclusive. To explore conditions under which verbal learning might occur, we hypothesized that peaks of slow waves would be conducive to verbal learning because the peaks define periods of neural excitability. While in slow-wave sleep during a nap, a series of word pairs comprising pseudowords, e.g., "tofer," and actual German words, e.g., "Haus" (house), were played to young German-speaking women and men. When the presentation of the second word of a pair (e.g., "Haus" of "tofer-house") coincided with an ongoing slow-wave peak, the chances increased that a new semantic association between the pair had been formed and retained. Sleep-formed associations translated into awake ones, where they guided forced choices on an implicit memory test. Reactivations of sleep-formed associations were mirrored by brain activation increases measured with fMRI in cortical language areas and the hippocampus, a brain structure critical for relational binding. We infer that implicit relational binding had occurred during peaks of slow oscillations, recruiting a hippocampal-neocortical network comparable to vocabulary learning in the waking state.

Preliminary evidence for physiological markers of implicit memory

The Concealed Information Test (CIT) aims to detect concealed knowledge and is known to be sensitive to explicit memory. In two experiments, we examined whether the CIT is also sensitive to implicit memory using skin conductance, respiration and heart rate measures. For each participant, previously studied items were either categorized as explicitly remembered, implicitly remembered or forgotten. The two experiments differed in the strength of memory encoding, the type of implicit memory test, the delay between study and test and the number of critical CIT items. The results of Experiment 1 revealed that CIT detection efficiency was weak and significant only in the explicit memory condition. In Experiment 2, however, CIT detection efficiency was stronger and significant in both the explicit and implicit memory conditions as indexed by skin conductance and respiration. Altogether, our results provide initial evidence that the CIT may be sensitive to implicit memory. Theoretical and practical implications are discussed.

Effects of Saccade Induced Retrieval Enhancement on conceptual and perceptual tests of explicit & implicit memory

The effects of saccadic horizontal (bilateral) eye movements upon tests of both conceptual and perceptual forms of explicit and implicit memory were investigated. Participants studied a list of words and were then assigned to one of four test conditions: conceptual explicit, conceptual implicit, perceptual explicit, or perceptual implicit. Conceptual tests comprised category labels with either explicit instructions to recall corresponding examples from the study phase (category-cued recall), or implicit instructions to generate any corresponding examples that spontaneously came to mind (category-exemplar generation). Perceptual tests comprised of word-fragments with either explicit instructions to complete these with study items (word-fragment-cued recall), or implicit instructions to complete each fragment with the first word that simply ‘popped to mind’ (word-fragment completion). Just prior to retrieval, participants were required to engage in 30 s of bilateral vs. no eye movements. Results revealed that saccadic horizontal eye movements enhanced performance in only the conceptual explicit condition, indicating that Saccade-Induced Retrieval Enhancement is a joint function of conceptual and explicit retrieval mechanisms. Findings are discussed from both a cognitive and neuropsychological perspective, in terms of their potential functional and neural underpinnings.

Influence of directed forgetting on implicit memory test of face

Influence of directed forgetting on implicit memory test of face

Older adults encode more, not less: evidence for age-related attentional broadening

ABSTRACTPrevious work has shown that older adults attend to and implicitly remember more distracting information than young adults; however, it is unknown whether they show a corresponding decrease in implicit memory for targets in the presence of distracters. Using implicit memory tests, we asked whether older adults show a tradeoff in memory between targets and distracters. Here, young and older adults performed a selective attention task in which they were instructed to attend to target pictures and ignore superimposed distracter words. We measured priming for distracter words using fragment completion and for target pictures using naming time. Older adults showed greater priming for distracting words compared to young adults, but equivalent priming for target pictures. These results suggest that older adults have a broader attentional scope than young adults, encompassing both relevant and irrelevant information.

Attempts to Suppress Episodic Memories Fail but do Produce Demand: Evidence from the P300-Based Complex Trial Protocol and an Implicit Memory Test.

Instructions to voluntarily suppress memories of a mock crime have been reported to result in decreased P300 amplitude during a P300-based concealed information test (CIT) and reduced autobiographical Implicit Association Test (aIAT) D scores, supporting successful suppression. However, one such study, (Hu et al., Psychological science 26(7):1098-1106, 2015) used the P300-based Complex Trial Protocol with a 50-50 target to nontarget ratio, which could impose much response switching and thereby drain cognitive resources, also resulting in reduced P300. The present study replicated Hu et al. (Psychological science 26(7):1098-1106, 2015) with one major variation-a less intrusive 20-80 target to nontarget ratio that required less response switching. Detection rates were high using both the brainwave-based CIT (90% accuracy) and the aIAT (87% accuracy). However we found no significant differences between the suppression and simple guilty groups on the major indices of concealed information detection, which compare probe and irrelevant P300 responses. While we did find that overall P300 amplitude was reduced in the suppression group, this reduction was not specific to probe responses. Additionally, while there were group differences in aIAT hit rates, there were no differences in aIAT D scores. Taken together, these findings suggest that the previously demonstrated reductions in P300 are a reflection of task demand rather than of effective voluntary memory suppression.

Stuck on semantics: Processing of irrelevant object-scene inconsistencies modulates ongoing gaze behavior.

People have an amazing ability to identify objects and scenes with only a glimpse. How automatic is this scene and object identification? Are scene and object semantics-let alone their semantic congruity-processed to a degree that modulates ongoing gaze behavior even if they are irrelevant to the task at hand? Objects that do not fit the semantics of the scene (e.g., a toothbrush in an office) are typically fixated longer and more often than objects that are congruent with the scene context. In this study, we overlaid a letter T onto photographs of indoor scenes and instructed participants to search for it. Some of these background images contained scene-incongruent objects. Despite their lack of relevance to the search, we found that participants spent more time in total looking at semantically incongruent compared to congruent objects in the same position of the scene. Subsequent tests of explicit and implicit memory showed that participants did not remember many of the inconsistent objects and no more of the consistent objects. We argue that when we view natural environments, scene and object relationships are processed obligatorily, such that irrelevant semantic mismatches between scene and object identity can modulate ongoing eye-movement behavior.

Effects of Divided Attention at Retrieval on Conceptual Implicit Memory.

This study investigated whether conceptual implicit memory is sensitive to process-specific interference at the time of retrieval. Participants performed the implicit memory test of category exemplar generation (CEG; Experiments 1 and 3), or the matched explicit memory test of category-cued recall (Experiment 2), both of which are conceptually driven memory tasks, under one of two divided attention (DA) conditions in which participants simultaneously performed a distracting task. The distracting task was either syllable judgments (dissimilar processes), or semantic judgments (similar processes) on unrelated words. Compared to full attention (FA) in which no distracting task was performed, DA had no effect on CEG priming overall, but reduced category-cued recall similarly regardless of distractor task. Analyses of distractor task performance also revealed differences between implicit and explicit memory retrieval. The evidence suggests that, whereas explicit memory retrieval requires attentional resources and is disrupted by semantic and phonological distracting tasks, conceptual implicit memory is automatic and unaffected even when distractor and memory tasks involve similar processes.

A novel test of implicit memory; an eye tracking study

Novelty preference in visual scanning behaviour is used to test implicit memory in patients with Alzheimer’s disease (AD). During the test, subjects are presented with slides that include both novel images and images that were seen before (repeated images). Slides are presented sequentially and the number of slides between the first and second presentations of repeated images is varied to mask the purpose of the test. The normalised average glance duration (N-AGD) on repeated images (the bias towards novelty) was used to measure novelty preference. Data from 10 young controls showed that the bias towards novelty is reduced as the number of slides between the first and second presentations of repeated images is increased. A group of 17 patients with AD showed no significant bias towards novelty while a group of 21 age matched controls do exhibit such bias (t(20) = 6.16, p < 0.001). The data suggest that patients with AD have no preference to novel images and support the idea that AD affects implicit memory. The receiver operator characteristics of the bias towards novelty showed that patients with AD and age-matched controls can be differentiated with both high sensitivity and high specificity.

Retrieval intention modulates the effects of directed forgetting instructions on recollection.

The neurocognitive basis of memory retrieval is often examined by investigating brain potential old/new effects, which are differences in brain activity between successfully remembered repeated stimuli and correctly rejected new stimuli in a recognition test. In this study, we combined analyses of old/new effects for words with an item-method directed-forgetting manipulation in order to isolate differences between the retrieval processes elicited by words that participants were initially instructed to commit to memory and those that participants were initially instructed to forget. We compared old/new effects elicited by to-be-forgotten (TBF) words with those elicited by to-be-remembered (TBR) words in both an explicit-memory test (a recognition test) and an implicit-memory test (a lexical-decision test). Behavioral results showed clear directed forgetting effects in the recognition test, but not in the lexical decision test. Mirroring the behavioral findings, analyses of brain potentials showed evidence of directed forgetting only in the recognition test. In this test, potentials from 450–650 ms (P600 old/new effects) were more positive for TBR relative to TBF words. By contrast, P600 effects evident during the lexical-decision test did not differ in magnitude between TBR and TBF items. When taken in the context of prior studies that have linked similar parietal old/new effects to the recollection of episodic information, these data suggest that directed-forgetting effects manifest primarily in greater episodic retrieval by TBR than TBF items, and that retrieval intention may be important for these directed-forgetting effects to occur.

Not all that glittered is gold: neural mechanisms that determine when reward will enhance or impair memory.

Not all that glittered is gold: neural mechanisms that determine when reward will enhance or impair memory.

Thalamic volume deficit contributes to procedural and explicit memory impairment in HIV infection with primary alcoholism comorbidity

Component cognitive and motor processes contributing to diminished visuomotor procedural learning in HIV infection with comorbid chronic alcoholism (HIV+ALC) include problems with attention and explicit memory processes. The neural correlates associated with this constellation of cognitive and motor processes in HIV infection and alcoholism have yet to be delineated. Frontostriatal regions are affected in HIV infection, frontothalamocerebellar regions are affected in chronic alcoholism, and frontolimbic regions are likely affected in both; all three of these systems have the potential of contributing to both visuomotor procedural learning and explicit memory processes. Here, we examined the neural correlates of implicit memory, explicit memory, attention, and motor tests in 26 HIV+ALC (5 with comorbidity for nonalcohol drug abuse/dependence) and 19 age-range matched healthy control men. Parcellated brain volumes, including cortical, subcortical, and allocortical regions, as well as cortical sulci and ventricles, were derived using the SRI24 brain atlas. Results indicated that smaller thalamic volumes were associated with poorer performance on tests of explicit (immediate and delayed) and implicit (visuomotor procedural) memory in HIV+ALC. By contrast, smaller hippocampal volumes were associated with lower scores on explicit, but not implicit memory. Multiple regression analyses revealed that volumes of both the thalamus and the hippocampus were each unique independent predictors of explicit memory scores. This study provides evidence of a dissociation between implicit and explicit memory tasks in HIV+ALC, with selective relationships observed between hippocampal volume and explicit but not implicit memory, and highlights the relevance of the thalamus to mnemonic processes.

Evaluation of the effects of anti-motion sickness drugs on subjective sleepiness and cognitive performance of healthy males

This study aimed to investigate the clinical and cognitive side effects of baclofen (10 mg), meclizine (25 mg), dimenhydrinate (40 mg) plus cinnarizine (25 mg) and promethazine (25 mg) plus d-amphetamine (10 mg). The study had a double-blind, placebo controlled, repeated measures design and was conducted on healthy male volunteers. The psychomotor vigilance test, the Sternberg working memory task, the implicit memory test and the automated Operation Span (Ospan) task were performed. The Stanford, the Karolinska and the Epworth Sleepiness scale determined the degree of sleepiness. The Profile of Mood States (POMS) evaluated mood states and adverse effects were reported on a 22-item questionnaire. Letter recalls and time for solving mathematical problems, recorded during the Ospan task, were impaired by baclofen and dimenhydrinate-cinnarizine respectively, suggesting an influence of these drugs on the working memory. Significant side effects for baclofen were: sleepiness, tiredness, blurred vision, concentration problems and dizziness whereas for dimenhydrinate-cinnarizine only sleepiness and blurred vision were reported. Meclizine decreased the accuracy on the Sternberg working memory task and thus seemed to affect short-term memory. A reported side effect was increased sleepiness. Promethazine plus d-amphetamine did not affect any of the tested cognitive functions. However, many side effects such as sleepiness, dry mouth, dizziness, vertigo, confusion, insomnia and tremors were reported. The results show that meclizine and dimenhydrinate combined with cinnarizine were the two drugs with the most acceptable combination of side effects.