Explicit Memory Tests Research Articles

The memory enhancement effect of emotion is absent in conceptual implicit memory.

Memory for emotional stimuli is superior to memory for neutral stimuli. This study investigated whether this memory advantage is present in implicit memory. Memory was tested with a test of explicit memory (associate cued recall) and a test of conceptual implicit memory (free association) identical in all respects apart from the retrieval instructions. After studying emotional and neutral paired associates, participants saw the first member of the pair, the cue; in the test of explicit memory participants were instructed to recall the associate; in the test of implicit memory participants were instructed to generate the first word coming to mind associated to the word. Depth of study processing dissociated performance in the tests, confirming that the free-association test was not contaminated by an intentional retrieval strategy. Emotional pairs were better recalled than neutral pairs in the test of explicit memory but not in the equivalent test of implicit memory. The absence of an emotion effect in implicit memory implies that emotional material does not have a privileged global mnemonic status; intentional retrieval is necessary for observing the emotion-related memory advantage.

The Asymmetric Relationship Between Encoding and Retrieval in Implicit and Explicit Memory

Encoding and retrieval are two important phases of memory.Encoding produces memory engraved and retrieval reactivates previously encoded information.The approach to the relationship between encoding and retrieval is meaningful for the better understanding of the nature of memory.As for explicit memory,the relation of encoding and retrieval has been investigated by many researchers who have found out that the performance of a secondary task during encoding reduced the later memory performance,but the division of the attention in the same way during retrieval had virtually no effect on memory performance,which indicated an asymmetry between encoding and retrieval processes.With respect to implicit memory,an asymmetry was also found in one of our previous studies(Meng Guo,2006),but the asymmetry is somewhat different from that in explicit memory,that is,the performance of a concurrent task during encoding had no effect on later task performance,but interference during retrieval disrupted priming,and reduced task performance.In order to clarify the issues we conducted an ERP experiment.The experiment was conducted with 16 undergraduate students as subjects and Chinese characters as stimuli.The experiment adopted a study-to-test paradigm,in which participants performed a "shallow"(color) study task or a "deep"(pleasant) study task,followed by either a lexical decision(implicit) test(section 1) or a recognition(explicit) test(section 2).In interference task participants were asked to account the total number of "+" in a regulated orientation which appeared with a word,and was performed concurrently with either the encoding or the retrieval phase of the memory task for encoding interference condition or retrieval interference condition.The results showed that:(1) the effects of interference to encoding in implicit memory test were different from that to retrieval.Interference during encoding had virtually no effect on N400 or P600 old/new ERP components,but interference during retrieval significantly reduced N400 old/new and P600 old/new components,which abolished behavior priming.(2) The effects of interference to encoding on ERP components in explicit memory test were different from that to retrieval.Interference during encoding had significant influence on later P600 old/new effect,but interference during retrieval did not produce such effect.The results confirmed the finding of Meng Guo(2006),that is,interference during encoding had effect on explicit memory,but left implicit memory intact.Interference during retrieval affected implicit memory,but had little effect on explicit memory.So the relationship between encoding and retrieval was different between implicit and explicit memory,thus providing further evidence on the dissociation between implicit and explicit memory.

The Long-Term Effect of Four Hours of Hyperventilation on Neurocognitive Performance and Lesion Size After Controlled Cortical Impact in Rats

We investigated the effects of 4 h of posttraumatic hyperventilation on neurocognitive performance, motor function, and coordination as well as lesion volume in rats subjected to focal traumatic brain injury. After a 14-day training period with various neurocognitive tests including hole-board, beam walk, and beam balance, 21 male Sprague-Dawley rats (369 +/- 15 g) were anesthetized with halothane, tracheally intubated, their lungs mechanically ventilated, and subjected to controlled cortical impact (1.75 mm depth, diameter 5 mm, 4 m/s). They were then randomized to either normoventilation (n = 10; PaCO(2) = 38-42 mm Hg) or hyperventilation (n = 11; PaCO(2) = 28-32 mm Hg) and ventilated for 4 h, respectively. Posttraumatic performance in the behavioral and motor tests was evaluated for 20 days. Rats were then decapitated under deep anesthesia, and their brains frozen and sliced to evaluate lesion volume. Hyperventilated animals performed significantly worse in explicit memory tests compared with normoventilated rats over time. Both groups showed deficits in advanced motor function and coordination (evaluated by beam walk and beam balance) initially, with a significantly worse performance of hyperventilated compared with normoventilated animals. However, there was no difference between groups by the end of the study. On Day 20 after injury, lesion volume was significantly larger with hyperventilated (69.7 +/- 13.0 mm(3)) compared with normoventilated animals (48.3 +/- 15.6 mm(3)). Although hyperventilation enhanced histologic damage, there was no long-term adverse neurocognitive effect from 4 h of posttraumatic hyperventilation (PaCO(2) = 28-32 mm Hg) in rats.

Differences of relevance in implicit and explicit memory tests: An ERP study

An ERP study was conducted to explore the differences between other-relevant words and possessor-relevant words in implicit and explicit memory tests. The results show that other-relevant words are associated with a more negative ERP than possessor-relevant words during 300-900 ms whether in the implicit or the explicit memory tests. The N400 effect is also found in semantic processing of social materials. There is an ERP dissociation of retrieval formats between the implicit and the explicit memory tests during 700-900 ms, namely, there is no difference between other-relevant words and possessor-relevant words in the implicit memory while there is a significant difference between them in the explicit memory. Observed through Curry 6.0, the analysis of neural sources for other-relevant words and possessor-relevant words indicates that they have different locations. At 400 ms, activity is found in the left precuneus during possessor-relevant words processing. Both the right and the left precuneus are activated during other-relevant words processing. However, at 600 ms their location is both in the left precuneus. In a word, our results show that there exists a cognitive difference between other-relevant words and possessor-relevant words, and other-relevant words closely related to the percipient himself/herself are strongly responded to, which reflects that there is a bigger attention bias to the stimuli concerning the percipient himself/herself than to processor-relevant words.

Inattentional blindness for ignored words: Comparison of explicit and implicit memory tasks

Inattentional blindness is described as the failure to perceive a supra-threshold stimulus when attention is directed away from that stimulus. Based on performance on an explicit recognition memory test and concurrent functional imaging data Rees, Russell, Frith, and Driver [Rees, G., Russell, C., Frith, C. D., & Driver, J. (1999). Inattentional blindness versus inattentional amnesia for fixated but ignored words. Science, 286, 2504–2507] reported inattentional blindness for word stimuli that were fixated but ignored. The present study examined both explicit and implicit memory for fixated but ignored words using a selective-attention task in which overlapping picture/word stimuli were presented at fixation. No explicit awareness of the unattended words was apparent on a recognition memory test. Analysis of an implicit memory task, however, indicated that unattended words were perceived at a perceptual level. Thus, the selective-attention task did not result in perfect filtering as suggested by Rees et al. While there was no evidence of conscious perception, subjects were not blind to the implicit perceptual properties of fixated but ignored words.

Levels of Processing and Amnesia Affect Perceptual Priming in Fragmented Picture Naming

In this paper we examine the impact of amnesia and of levels of processing on implicit memory by using a well-established fragmented picture-naming test with proven adequate reliability. A group of patients with amnesia of non-Korsakoff etiology was compared to a control group. While amnesic patients showed a deficit in perceptual priming, both groups showed a comparable level of processing effect. Our results confirm that when a reliable implicit memory test is used amnesia and levels of processing can both be shown to affect implicit memory performance. Thus, functional dissociations between explicit and implicit memory tests may be the consequence of a methodological artifact, that is, a difference in the reliability of the tests.

Syndrome démentiel dans les suites d’une bipolarité

Converging evidence suggests that people with bipolar disorder (BPD) exhibit persistent cognitive impairment independently from the emotional state. In old age BPD, the cognitive decline is more severe and can fulfill the criteria of dementia. However, the characteristics of bipolar disorder dementia are still unknown. The aim of the study was to characterise the cognitive and imaging profile of the dementia following bipolar disorder. Patients fulfilling criteria of dementia and followed-up in the memory unit for at least two years were included. Patients with substance abuse were excluded. A battery of specific (assessing verbal memory, attention, frontal executive function, construction and visuospatial impairment), and global (MMSE and Mattis dementia rating scale) neuropsychological tests, behavioural assessment using the frontotemporal behavioural scale, MRI and HMPAO-SPECT imaging were performed in all patients during euthymic state. We included 13 patients with bipolar disorder (9W/4M). The mean age was 70.8 years (+/-7.7). Dementia began in average 29.2 years (+/-10.1) after the onset of the bipolar disorder. The mean score of MMSE was 24.0 (+/-4.3). The mean score of the Mattis dementia rating scale was 122.5 (+/-8.9). After an average of 6.1 years (+/-2.8) of follow-up, the mean score of MMSE was 23.5 (+/-3.2). The annual MMSE score decrease was of 0.5 (+/-4.4) per year. In more than 75% of the patients, Trail-Making Test-part B, Go-nogo test, Stroop test, delayed free recall in verbal explicit long-term memory test, category fluency tasks and code test were impaired. In more than 50% of patients, free recall, delayed cued recall, clock test, visuospatial battery and temporal orientation were impaired. On the other hand, spatial orientation and recognition were within the standards. The mean of the BREF score was 10.6 (+/-3.2). A moderate frontal behavioural syndrome was observed, but never persistent hallucinations. Seven patients had been treated with lithium and seven with antipsychotics, but none during the neurological assessment. Moderate extrapyramidal signs were reported in 10 patients, of which the seven patients treated in the past with antipsychotics. MRI showed no focal atrophy and no vascular lesions. Functional imaging conducted in 10 patients always showed uptake decrease in the frontotemporal regions and sometimes in the parietal region too. After six years of follow-up, no patient fulfilled the probable criteria for the main dementia, Alzheimer disease, vascular dementia, frontotemporal dementia and dementia with Lewy bodies. The data of this study support a possible specific dementia postbipolar disorder and not only mild cognitive decline. This hypothesis could be tested in a prospective study. Such dementia could be a main differential diagnosis from long lasting frontotemporal dementia. The pathogenic process of this dementia could also be determined.

Memory bias for health-related information in somatoform disorders

Objective Cognitive processes are considered to be relevant to the etiology and maintenance of somatoform disorders (SFDs). The aim of this study was to assess explicit and implicit information-processing bias for disorder-congruent information in SFDs. Methods A clinical sample of 33 patients suffering from multiple somatoform symptoms (SSI-3/5) and 25 healthy controls performed an encoding task with computer-presented word lists (illness related, negative, positive, neutral content), subsequently followed by explicit memory tests (free recall and recognition) and an implicit test (word-stem completion). Results The somatoform group showed a memory bias for illness-related stimuli in the word-stem completion task, whereas the two groups did not differ in explicit memory tests. This effect could not be explained by comorbid depression. Conclusion These results provide some support for current theories on SFDs.

Capturing conceptual implicit memory: The time it takes to produce an association

Conceptual implicit memory is demonstrated when, in the absence of explicit retrieval, performance on a task requiring conceptual processing benefits more from prior conceptual encoding than from prior nonconceptual encoding. In the present study, we sought to provide an improved measure of conceptual implicit memory by minimizing contamination from explicit retrieval. On a modified word association test, participants free-associated to the actually studied items, with response time to produce any associate serving as the dependent measure. Experiment 1 varied whether words were read or generated at study and showed that generated words were associated to more quickly than were read words. Experiment 2 varied level of processing at study and showed that words processed semantically were associated to more quickly than were words processed nonsemantically. With modifications to ensure its implicit nature, a conceptual implicit test can be consistently affected by the same encoding manipulations as those that affect conceptual explicit memory tests.

Environmental context effects in conceptual explicit and implicit memory

Previous research has found environmental context effects for both conceptual explicit and conceptual implicit memory (Parker, Gellatly, & Waterman, 1999). The research presented here challenges these findings on methodological grounds. Experiment 1 assessed the effects of context change on category-exemplar generation (conceptual implicit memory test) and category-cued recall (conceptual explicit memory test). Experiment 2 assessed the effects of context change on word association (conceptual implicit memory test) and word associate cued recall (conceptual explicit memory test). In both experiments, study–test changes in environmental context were found to influence performance only on tests of explicit memory. It is concluded that when retrieval cues across explicit and implicit tests are matched, and the probability of explicit contamination is reduced, then only conceptual explicit test performance is reduced by study–test changes in environmental context.

Dissociable effects of conscious emotion regulation strategies on explicit and implicit memory.

The authors manipulated emotion regulation strategies at encoding and administered explicit and implicit memory tests. In Experiment 1, participants used reappraisal to enhance and decrease the personal relevance of unpleasant and neutral pictures. In Experiment 2, decrease cues were replaced with suppress cues that directed participants to inhibit emotion-expressive behavior. Across experiments, using reappraisal to enhance the personal relevance of pictures improved free recall. By contrast, attempting to suppress emotional displays tended to impair recall, especially compared to the enhance condition. Using reappraisal to decrease the personal relevance of pictures had different effects depending on picture type. Paired with unpleasant pictures, the decrease cue tended to improve recall. Paired with neutral stimuli, the decrease cue tended to impair recall. Emotion regulation did not affect perceptual priming. Results highlight dissociable effects of emotion regulation on explicit and implicit memory, as well as dissociations between regulation strategies with respect to explicit memory.

Autobiographical memory deficit in anorexia nervosa: Emotion regulation and effect of duration of illness

Emotional deficits in anorexia nervosa can be expressed in autobiographical memory recall. The aim of this study is to test whether deficits in autobiographical memory exist in anorexic patients and concern specifically negative or positive emotional valence. Moreover, it is unclear whether these deficits are dependent upon comorbid aspects (depression, alexithymia, and anxiety) or upon illness duration. Anorexic patients ( n=25) were compared to healthy volunteers based on their clinical assessment, explicit memory test score, and autobiographical memory test score. The study makes use of the autobiographical test of Williams and Scott, which involves specific emotional cues to elicit memory. Anorexic patients recalled more general memories than controls in autobiographical memory test, but had no deficit in explicit memory test. This pattern, observed both for negative and positive cues, was neither related to depression or alexithymia, nor to anxiety severity, but increased significantly with illness duration. These results show that anorexic patients are characterized by relative difficulty in the integration of both negative and positive emotional experiences, and that this impairment is reinforced by illness duration.

Ageing affects conceptual but not perceptual memory processes

Whereas age effects commonly occur in tests of explicit memory, tests of implicit memory often show age invariance. In two experiments, the traditional confound between test type (implicit vs explicit) and retrieval process (conceptually driven vs perceptually driven) was removed by using conceptually driven and perceptually driven tests of both implicit and explicit memory. Experiment 1 revealed a significant age effect for conceptually driven retrieval and no age effect for perceptually driven retrieval, regardless of the type of memory being measured. Experiment 2 highlighted a difference between the two age groups in their ability to utilise semantic encoding in a nominally perceptually driven explicit memory test. The paper concludes that although perceptually driven processing is stable over age, particular care must be taken to minimise contamination from conceptually driven retrieval processes in such investigations.

Endogenous versus exogenous attentional cuing effects on memory

Three experiments were conducted to investigate the influence of early attentional cuing effects on subsequent memory. In an incidental study phase, a cue preceded two simultaneously displayed words. An endogenous cue (row of arrows pointing toward one word) or an exogenous cue (row of stars at the location of one word) indicated which word to read aloud. In a subsequent test phase, memory for these cued and uncued words was measured. In Experiment 1, these attentional manipulations had almost no effect on subsequent implicit memory measured using a speeded reading (naming) test. Experiments 2 and 3 demonstrated that, on an explicit memory test, words were reliably better recognized in the endogenous condition than in the exogenous condition. These results suggest that endogenous attentional cues promote more active processing and hence elaboration of words, assisting their subsequent conscious retrieval.

Event-related fMRI of category learning: Differences in classification and feedback networks

Eighteen healthy young adults underwent event-related (ER) functional magnetic resonance imaging (fMRI) of the brain while performing a visual category learning task. The specific category learning task required subjects to extract the rules that guide classification of quasi-random patterns of dots into categories. Following each classification choice, visual feedback was presented. The average hemodynamic response was calculated across the eighteen subjects to identify the separate networks associated with both classification and feedback. Random-effects analyses identified the different networks implicated during the classification and feedback phases of each trial. The regions included prefrontal cortex, frontal eye fields, supplementary motor and eye fields, thalamus, caudate, superior and inferior parietal lobules, and areas within visual cortex. The differences between classification and feedback were identified as (i) overall higher volumes and signal intensities during classification as compared to feedback, (ii) involvement of the thalamus and superior parietal regions during the classification phase of each trial, and (iii) differential involvement of the caudate head during feedback. The effects of learning were then evaluated for both classification and feedback. Early in learning, subjects showed increased activation in the hippocampal regions during classification and activation in the heads of the caudate nuclei during the corresponding feedback phases. The findings suggest that early stages of prototype-distortion learning are characterized by networks previously associated with strategies of explicit memory and hypothesis testing. However as learning progresses the networks change. This finding suggests that the cognitive strategies also change during prototype-distortion learning.

Implicit Memory Development in School-Aged Children With Attention Deficit Hyperactivity Disorder (ADHD): Conceptual Priming Deficit?

Previous research has shown that children with attention deficit hyperactivity disorder (ADHD) often demonstrate performance deficits on effortful, strategic memory tasks, whereas relatively rote tasks of memory reveal no such deficit. Thus far, research in this domain has focused primarily on explicit memory. This study examined performance on multiple measures of implicit and explicit memory in children aged 7 to 14 years with and without ADHD. Memory for words and pictures was assessed at 15-min and 24-hr intervals. ADHD and non-ADHD groups performed similarly on tests of explicit memory (category-cued recall and recognition) and on perceptual aspects of implicit memory (word stem completion and picture fragment identification) as a function of age, retention interval, and stimulus format (i.e., picture or word). However, there was no evidence of priming on a conceptual implicit memory test (category exemplar generation) for boys with ADHD. This type of conceptual task, which is likely mediated by frontal systems, may indicate a unique memory deficit associated with ADHD.

The Effect of Moderate to Severe Traumatic Brain Injury (TBI) on Different Aspects of Memory:A Selective Review

Deficient learning and memory are frequently reported as a consequence of traumatic brain injury (TBI). Because of the diffuse nature of the injury, patients with TBI are not the ideal group for studying brain-behavior relations. Nevertheless, characterization of the memory breakdown following TBI could contribute to the assessment and rehabilitation of this patient population. It is well documented that memory is not a unitary system. Accordingly, in this article I review studies that have investigated the long-term effect of moderate to severe TBI on different memory aspects, including explicit and implicit tests of memory. This review demonstrates that TBI affects a large range of memory aspects. One of the conclusions is that the memory impairment observed in TBI patients could be viewed, at least to some degree, as a consequence of a more general cognitive deficit. Thus, unlike patients suffering from global amnesia, memory in patients with TBI is not selectively impaired. Nevertheless, it is possible to detect a subgroup of patients that do meet the criteria of amnesia. However, the most common vulnerable memory processes following TBI very much resemble the memory deficits reported in patients following frontal lobe damage, e.g., difficulties in applying active or effortful strategy in the learning or retrieval process. The suggested similarity between patients with TBI and those suffering from frontal lobe injury should be viewed cautiously; considering the nature of TBI, patients suffering from such injuries are not a homogeneous group. In view of this limitation, the future challenge in this field will be to identify subgroups of patients, either a priori according to a range of factors such as severity of injury, or a posteriori based on their specific memory deficit characteristics. Such a research approach has the potential of explaining much of the variability in findings reported in the literature on the effect of TBI on memory. This work was supported by the Paula Rich Multidisciplinary Center in Mind, Brain and Behavior, Bar-Ilan University, Ramat-Gan, Israel. The author thanks Mr. Judah Koller for his help with the preparation of the tables.

Cognitive discernible factors between schizophrenia and schizoaffective disorder

Background Schizophrenia (SZ) and schizoaffective disorders (SA) are associated with cognitive deficits. Generally, a schizoaffective diagnosis is associated with better prognosis on the level of social integration. It is also well established that cognition is an important factor for good social outcome in schizophrenia. We hypothesized that, although patients suffering from SA share symptoms with SZ, they can be differentiated on the basis of neurocognitive function and that SA perform better in several domains. Method Performances of two groups SA ( N = 13) and SZ ( N = 44) were compared on several visual-motor tasks using CANTAB [Motor Screening (MOT), Reaction Time (RTI), Paired Associates Learning Task (PAL), and Stockings of Cambridge items (SOC)]. The two groups were matched for symptom severity. ANOVA with repeated measures was employed to determine whether any difference in cognitive scores during a 2-year period was significantly related to the diagnostic status. Results A significant and durable difference was observed between SZ and SA on motor screening and explicit memory tests where SA performed better. Conclusion Neurocognitive tests may be relevant for distinguishing schizoaffective from schizophrenia, chiefly via tests tapping into visuo-spatial and visuo-motor coordination abilities (e.g., paired associated learning and motor screening).

Retrieval-induced forgetting in implicit memory tests: The role of test awareness

Retrieval practice with particular items in memory may result in decreased recall of different, semantically related, items. This retrieval-induced forgetting effect has been demonstrated in studies using explicit memory tests. Anderson and Spellman (1995) have attributed retrieval-induced forgetting to inhibitory mechanisms. This hypothesis predicts similar effects in implicit memory tasks. In our first experiment, using Anderson and Spellman's original paradigm, retrieval-induced forgetting was found using an explicit memory test with independent extralist retrieval cues. In our second experiment, using the same materials, retrieval-induced forgetting was also found using an implicit memory test with independent extralist retrieval cues, but only for participants who were aware of the relationship between the study and practice phase on the one hand, and the test phase of the experiment on the other. Thus, test awareness seems to mediate retrieval-induced forgetting in implicit memory tasks.

A mixed-handed advantage in episodic memory: A possible role of interhemispheric interaction

Recent behavioral and brain imaging data indicate that performance on explicit tests of episodic memory is associated with interaction between the left and right cerebral hemispheres, in contrast with the unihemispheric basis for implicit tests of memory. In the present work, individual differences in strength of personal handedness were used as markers for differences in hemispheric communication, with mixed-handers inferred to have increased interhemispheric interaction relative to strong right-handers. In Experiment 1, memory for words was assessed via recall or word fragment completion. In Experiment 2, memory for real-world events was assessed via recall. Results supported the hypothesis, in that mixed-handers displayed better episodic memory in comparison with strong right-handers.