Only explicit memory seems affected by depth of hypnotic state.

Attending to Remember and Remembering to Attend

ABSTRACTIntroduction: Previous studies have found that music paired with lyrics at encoding may improve the memory performance of patients with mild Alzheimer’s disease (AD). To further explore memory for different types of musical stimuli, the current study examined both implicit and explicit memory for music with and without lyrics compared to spoken lyrics.Method: In this mixed design, patients with probable mild AD (n = 15) and healthy older adults (n = 13) listened to auditory clips (song, instrumental, or spoken lyrics varied across three sessions) and then had their memory tested. Implicit memory was measured by the mere exposure effect. Explicit recognition memory was measured using a confidence-judgment receiver operating characteristic (ROC) paradigm, which allowed examination of the separate contributions made by familiarity and recollection.Results: A significant implicit memory mere exposure effect was found for both groups in the instrumental and song but not the spoken condition. Both groups had the best explicit memory performance in the spoken condition, followed by song, and then instrumental conditions. Healthy older adults demonstrated more recollection than patients with AD in the song and spoken conditions, but both groups performed similarly in the instrumental condition. Patients with AD demonstrated more familiarity in the instrumental and song conditions than in the spoken condition.Conclusions: The results have implications for memory interventions for patients with mild AD. The implicit memory findings suggest that patients with AD may still show a preference for information familiar to them. The explicit memory results support prior findings that patients with AD rely heavily on familiarity, but also suggest that there may be limitations on the benefits that music can provide to recognition memory performance.

Twenty patients with primary insomnia were compared with 20 normal controls, matched for age, sex, and educational level, on a modified version of the emotional Stroop test, and tests of explicit and implicit memory for threat words and non-threat words. The results showed that the insomniacs had a prolonged Stroop latency for sleep words, but so did the controls, and there was no group difference on Stroop interference of sleep words. The insomniacs showed no explicit or implicit memory bias for threat words, and they did not differ from the controls on explicit or implicit memory performance. They did differ from the controls, however, by scoring lower on the WAIS-R vocabulary test, and by having lower expectations of their explicit memory performance before testing, although they did not differ from the controls on how they evaluated their memory performance after testing. The results are discussed in terms of a possible deficit in semantic memory in insomniacs.

Intact and impaired conceptual memory processes in amnesia.

According to the traditional memory-systems view, the hippocampus is critical during explicit (conscious) long-term memory, whereas other brain regions support implicit (nonconscious) memory. In the last two decades, some fMRI studies have reported hippocampal activity during implicit memory tasks. The aim of the present discussion paper was to identify whether any implicit memory fMRI studies have provided convincing evidence that the hippocampus is associated with nonconscious processes without being confounded by conscious processes. Experimental protocol and analysis parameters included the stimulus type(s), task(s), measures of subjective awareness, explicit memory accuracy, the relevant fMRI contrast(s) or analysis, and confound(s). A systematic review was conducted to identify implicit memory studies that reported fMRI activity in the hippocampus. After applying exclusion criteria, 13 articles remained for analysis. We found that there were no implicit memory fMRI studies where subjective awareness was absent, explicit memory performance was at chance, and there were no confounds that could have driven the observed hippocampal activity. The confounds included explicit memory (including false memory), imbalanced attentional states between conditions (yielding activation of the default-mode network), imbalanced stimuli between conditions, and differential novelty. As such, not a single fMRI study provided convincing evidence that implicit memory was associated with the hippocampus. Neuropsychological evidence was also considered, and implicit memory deficits were caused by factors known to disrupt brain regions beyond the hippocampus, such that the behavioral effects could not be attributed to this region. The present results indicate that implicit memory is not associated with the hippocampus.

A recent study in young patients undergoing propofol-alfentanil-nitrous oxide anaesthesia demonstrated implicit memory for stories presented during operation using a postoperative reading speed task. In this study we investigated whether patients who tolerate only small amounts of anaesthetics are prone to develop implicit and explicit memories about intraoperative events. Thirty patients with poor physical status (ASA III-IV) undergoing cardioverter defibrillator implantation were included in the study. Patients were premedicated with intravenous midazolam and anaesthesia was maintained using propofol and remifentanil infusions. During surgery one of two audio-tapes containing two short stories was played to the patients. Reading speed for the stories played during surgery and two similar stories from the other tape was tested 4 h later. Explicit memory was tested at 4 h and 24 h after audiotape presentation using a structured interview and a forced-choice recognition test pertaining to the story content. Thirty additional awake subjects served as controls. Although half of the patients seemed to be awake one or more times during the operation, no explicit memories of intraoperative events were reported. The forced-choice recognition of the stories was at chance level. No effect on reading speed was found in either the patients or the control subjects. The possible reasons for reduced explicit and implicit memory performance in elderly patients are age and poor physical status of the patients and the modality change between study and test phases. A non-anaesthetised control group of the same age and physical status should therefore be included in all studies of implicit memory.

Implicit and explicit olfactory memory in people with and without Down syndrome

The present research was designed to provide a direct test of the transfer-appropriate processing framework as it applies to performance on two implicit memory tasks and also to identify the component processes that are engaged on these memory tasks. The general strategy involved employing study tasks that mimicked (more so than a standard Read condition) the processing that appears to occur during the memory task. Performance on a stem-- completion task was not consistently enhanced by a study task in which participants selected potential word endings for the three-letter stems. However, inducing participants to engage in a letter-substitution task during encoding enhanced priming on a fragment-completion test, relative to the standard Read condition. Consistent with the transfer-- appropriate processing framework, the letter-substitution task showed evidence of optimizing priming effects, as additional manipulations of similarity had no further effect on performance on the implicit test. The data suggest that the Read condition does not induce maximum processing, as has been suggested previously, whereas a letter-by-letter substitution strategy mimics the processes used to complete word fragments on an implicit test. However, participants may not normally solve word stems by generating possible word endings and then selecting among these alternatives. Implicit memory tasks are operationally defined as memory tests for which the participant is given no instructions to consciously retrieve information from a prior study list, even though performance on the test may be affected by exposure to the prior study list. By contrast, explicit memory tests are defined as those for which the participant is given instructions at test to retrieve previously studied information (e.g., Richardson-Klavehn & Bjork, 1988). Although everyday uses of memory likely establish a predominant role for implicit memory (see also Masson & Graf, 1993), the extensive theoretical and empirical interest in implicit test performance over the last several years appears to have been motivated by two findings in particular. First, it is now well-established that individuals suffering from amnesia show performance on implicit memory tests that often does not differ from that of people with normal memory function (Morris & Kopelman, 1986; Richardson-- Klavehn & Bjork, 1988; Schacter, 1987; Shimamura, 1986, 1993). Although there are a few exceptions to this pattern (e.g., Hamann & Squire, 1996; Hodges, Salmon, & Butters, 1992), the generalization holds across a large number of etiological bases for the amnesia, including most forms of temporary and permanent amnesia. The second reason for interest in implicit memory is the finding that many independent variables have different effects on implicit and explicit memory performance. This research has been summarized in several places (e.g., Roediger & McDermott, 1993). Of primary relevance to the present work is the finding that performance on most tests of implicit memory is driven primarily by processing of the stimulus whereas performance on most tests of explicit memory is driven primarily by conceptual processing. Several aspects of processing have been shown to affect performance on these implicit memory tests, including typographic format (e.g., Clarke & Morton, 1983; Graf & Ryan, 1990; Jacoby & Hayman, 1987) and modality (e.g., Graf, Shimamura, & Squire, 1985; Jacoby & Dallas, 1981; Roediger & Blaxton, 1987). In contrast, conceptual processing yields much larger effects on explicit memory tasks than on implicit memory tasks (e.g., Gellatly, Parker, Blurton, & Woods, 1994). One of the most widely cited examples of this is the manipulation of depth of processing at study: Whereas depth effects are well-established on explicit tasks (e.g., Craik & Tulving, 1975), they are generally much smaller or even nonexistent on standard perceptual implicit tasks (for reviews, see Brown & Mitchell, 1994; Challis & Brodbeck, 1992; see also Hamann & Squire, 1996; Thapar & Greene, 1994). …

This study explored the nature of the relationship between attention available at learning and subsequent implicit and explicit memory performance. One hundred neurologically normal subjects rated their liking of target words on a five-point scale. Half of the subjects completed the word-rating task in a full attention condition and the other half performed the task in a divided attention condition. Following administration of the word-rating task, all subjects completed five memory tests, three implicit (category association, tachistoscopic identification, and perceptual clarification) and two explicit (semantic-cued recall and graphemic-cued recall), each bearing on a different subset of the list of previously presented target words. The results revealed that subjects in the divided attention condition performed significantly more poorly than subjects in the full attention condition on the explicit memory measures. In contrast, there were no significant group differences in performance on the implicit memory measures. These findings suggest that the attention to an episode that is necessary to produce later explicit memory may differ from that necessary to produce unconscious influences. The relationship between implicit memory, neurologic injury and automatic processes is discussed.

The distinction between explicit and implicit memory is fundamental to current memory research. Explicit memory involves conscious remembering of prior episodes, often by means of intentional retrieval of those episodes, whereas implicit memory involves influences of prior episodes on current behaviour without intentional retrieval, and sometimes without conscious remembering of those prior episodes. Much evidence confirms that explicit memory and implicit memory have different neural bases at the retrieval stage, but what about the encoding stage? Little evidence is provided owing to methodological ambiguities in prior studies which often compared incidental tests with intentional tests. In fact, brain activity in one test can reflect not only implicit (memory) but also explicit memory. Addressing these ambiguities has awaited a theoretical approach that distinguishes implicit (memory) and explicit memory for specific episodes in one test. To explore this question, a forced-choice recognition was conducted to produce priming without awareness of memory retrieval. We suggest that recognition mechanisms allied with explicit memory are different from recognition mechanisms allied with implicit memory. An ERP experiment was conducted with a study-to-test paradigm, in which participants performed a color study task, followed by a forced-choice recognition. There are two stages during recognition. Two words (one old and one new) were presented in a forced-choice recognition, and subjects were asked to choose the old one. If subjects could not choose a studied word, they were encouraged to guess. After choosing, subjects would report whether the word was from the study stage or not. Neural activities during the study phase were recorded. The Dm for explicit memory was identified by contrasting ERPs to words for which the studied word was selected and endorsed it as an old word versus ERPs to words for which the studied word was unselected; The Dm for implicit memory was identified by contrasting ERPs to words for which the studied word was selected but failed to endorse it as an old word versus ERPs to words for which the studied word was unselected. The results showed that implicit and explicit memory share a 200~300ms frontal-central negative-going Dm effect, which maybe reflect attention at encoding, so that these words can be retrieved implicitly or explicitly. Implicit memory involved a temporal negative-going Dm effect from 200ms after stimulus onset, which maybe reflect encoding into the perceptual representation system. Explicit memory involved an earlier (400-600ms) right prefrontal, positive-going Dm effect, as well as a late (600-1200ms) parietal negative-going Dm effect. These effects maybe reflect elaborated processing and encoding into the episodic memory system. The results suggested that implicit and explicit memory are not completely independent of each other. The truth is that they have both independent and shared components at encoding.

The aim of this study was to investigate the effect of emotional load of words (positive, negative and neutral) on explicit and implicit memory performances of participants with low and high alexithymia levels. The sample of the study consisted of 381 participants who were undergraduate students studying at Aydın Adnan Menderes University (M = 20.48, S = 1.73), with the age range between 18 and 26, and the second stage was consisted of 95 participants (M = 21,07, S = 2.21) with the age range between 18 and 26. Demographic Information Form and Toronto Alexithymia Scale were applied to the participants at the first stage. Participants who obtained one standard deviation below and above from Toronto Alexithymia Scale were invited to the second stage. Then the word completion task (implicit memory task) and free recall task (explicit task) were applied. The experimental design was 2 (Alexithymia Lev-el: low and high) x 3 (Emotional Use of Words: positive, negative, neutral) mixed ANOVA. The results showed significant difference between low and high alexithymia on explicit memory task. Participants with high levels of alexithymia remembered fewer words than those with low levels. There was no significant difference in neutral words on the main effect of emotional load according to alexithymia level. However, the group with high alexithymia remembered positive and negative words less than neutral words as compared to low alexithymia group. There was no significant difference in implicit memory performance according to interaction effect of alexithymia level and emotional load. Findings showed that high alexithymia level caused a deterioration on explicit memory but did not cause an impairment on implicit memory. The effect of alexithymia level on performance of remembering emotional words in explicit memory and implicit memory tasks was discussed in the light of emotional memory enhancement effect and related literature.

Using the Process Dissociation Procedure: The Meaning and Value of Comparable Base Rates

Effects of full and divided attention during study on explicit and implicit memory performance were investigated in two experiments. Study time was manipulated in a third experiment. Experiment 1 showed that both similar and dissociative effects can be found in the two kinds of memory test, depending on the difficulty of the concurrent tasks used in the divided-attention condition. In this experiment, however, standard implicit memory tests were used and contamination by explicit memory influences cannot be ruled out. Therefore, in Experiments 2 and 3 the process dissociation procedure was applied. Manipulations of attention during study and of study time clearly affected the controlled (explicit) memory component, but had no effect on the automatic (implicit) memory component. Theoretical implications of these findings are discussed.

Introduction: In a previous study, we found significant implicit memory in patients undergoing cardiac surgery. [1] While the bispectral index (BIS) of EEG has been correlated with loss of consciousness in anesthetized patients it is not clear whether the level of intraoperative implicit memory correlates with this measure of hypnotic state. [2,3] In this study, we determined the extent of intraoperative implicit and explicit memory formation in relation to the patient's BIS scores under general anesthesia for elective cardiac surgery. We hypothesized that higher BIS scores would predict the presence of implicit memory. Methods: After institutional review board approval, written informed consent was obtained from 11 patients. Subjects were randomized to receive one of two different audiotapes of 15 associated word pairs [4] and either a low (40) or high (60) target BIS condition. One complete presentation of the word list took 66 seconds. Anesthesia was induced and maintained (mean total dose +/- SD) using fentanyl (40.9 +/- 10.8 mcg/kg), midazolam (18.7 +/- 4.4 mcg/kg), and isoflurane ([0.0 - 0.4]exp). On approximately postoperative day 4 (range 3 - 6) a blinded observer performed memory testing. For implicit memory, patients free associated cues from the 15 cue-target word pairs presented and the 15 pairs not-presented during surgery. To measure explicit memory, recall and recognition tasks were given. The level of implicit memory was indicated by percentage of correct associations for presented items minus that for not presented items. Explicit memory was measured in terms of hits minus false alarms. Results: BIS values were obtained at 2.5 minute intervals and mean BIS scores were calculated for the period of list presentation. For the implicit task, patients randomized to the high BIS condition (54.7 +/- 4.6, n = 6) reported more correct target words for the presented than for the not-presented cues (7.7 +/- 2.3 vs 6.7 +/- 2.7, p = 0.14) while patients in the low BIS condition (42.0 +/- 1.9, n = 5) did not (5.3 +/- 3.7 vs 5.7 +/- 3.5, p = 0.77). The four patients who had BIS scores >or=to 70 during 2 - 5% of the recording period showed significant differences in performance for the presented and not-presented lists (mean difference 5.8 +/- 1.7, p = 0.006). No patient demonstrated spontaneous or directed evidence of explicit memory. Conclusion: Our preliminary results suggest that higher BIS levels enabled preserved implicit memory. Since patients with transient BIS levels > 70 showed significant levels of implicit memory, they were reliably able to reinforce associations between word pairs solely on the basis of their intraoperative auditory presentation. Although the clinical significance of implicit memory and its relationship to assessments of "depth of anesthesia" awaits further control experiments, it appears that BIS levels can aid in predicting the presence or absence of intraoperative implicit memory.

There is evidence that the prevention of errors during learning might be helpful in improving an impaired memory performance, both in amnesia as well as in normal age-related memory decline. Although errorless learning is a promising technique for use in rehabilitation practice, the underlying mechanisms are unclear. That is, it has been suggested that the beneficial effects of errorless learning operate through implicit memory, whereas others implicate that it is explicit memory that is responsible for the enhanced memory performance after errorless learning. The current study examined the contribution of implicit and explicit memory function to the memory performance after errorless and errorful learning using the process-dissociation procedure. A group of young adults (N=40) was compared to a matched group of older individuals (N=40) on a spatial memory task (i.e., learning the locations of everyday objects in a room). The results clearly show age-related decline in explicit spatial memory, while implicit spatial memory was unaffected. Furthermore, the young group benefited from errorless learning compared to errorful learning, while the older group did not show a difference between the two learning conditions. Also, it was found that the effects of errorful learning were related to explicit memory function, and not implicit processing, corroborating and extending recent findings.