Implicit and explicit memory bias in anxiety: A conceptual replication

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.

In the absence of explicit memories such as the recall and recognition of intraoperative events, memory of auditory information played during general anesthesia has been demonstrated with several tests of implicit memory. In contrast to explicit memory, which requires conscious recollection, implicit memory does not require recollection of previous experiences and is evidenced by a priming effect on task performance. The authors evaluated the effect of a standardized anesthetic technique on implicit memory, first using a word stem completion task, and then a reading speed task in a subsequent study. While undergoing lumbar disc surgery, 60 patients were exposed to auditory materials via headphones in two successive experiments. A balanced intravenous technique with propofol and alfentanil infusions and a nitrous oxide-oxygen mixture was used to maintain adequate anesthesia. In the first experiment, 30 patients were exposed randomly to one of the two lists of 34 repeated German nouns; in the second experiment, 30 patients were exposed to one of two tapes containing two short stories. Thirty control patients for each experiment heard the tapes without receiving anesthesia. All patients were tested for implicit memory 6-8 h later: A word stem completion task for the words and a reading speed task for the stories were used as measures of implicit memory. The control group completed the word stems significantly more often with the words that they had heard previously, but no such effect was found in the anesthetized group. However, both the control and patient groups showed a decreased reading time of about 40 ms per word for the previously presented stories compared with the new stories. The patients had no explicit memory of intraoperative events. Implicit memory was demonstrated after anesthesia by the reading speed task but not by the word stem completion task. Some methodologic aspects, such as using low frequency words or varying study and test modalities, may account for the negative results of the word stem completion task. Another explanation is that anesthesia with propofol, alfentanil, and nitrous oxide suppressed the word priming but not the reading speed measure of implicit memory. The reading speed paradigm seems to provide a stable and reliable measurement of implicit memory.

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

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

Cognitive processes play an important role in the etiology and maintenance of anxiety and depression. Current theories differ, however, in their predictions regarding the occurrence of attentional biases and memory biases in depression and anxiety. To allow for a systematic comparison of disorders and cognitive processes, 117 women (35 with generalized social phobia, 27 with major depression, and 55 healthy controls) participated in a test of visual attention (visual search), an explicit memory test (free recall), and an implicit memory test (anagram solving). Both clinical groups exhibited attentional biases for disorder-related words, whereas only depressed participants showed clear evidence of explicit and implicit memory biases. The implications of these results for competing theories are discussed.

Neural Correlates of Perceptual/Semantic Encoding and Implicit/Explicit Retrieval: An fMRI Study T. Park (tpark@chonnam.ac.kr) Department of Psychology, Chonnam National University Kwangju 500-757, Republic of Korea The important distinction between implicit and explicit memory tests is based on intentional effort and conscious recollection experience during retrieval process (Schacter, 1987), which have been suggested to be associated with increased activity in prefrontal and medial temporal regions, respectively (Schacter & Buckner, 1998). The present study investigated brain areas activated during tasks involving implicit and explicit memory retrieval, and examined neural correlates of conscious recollection and intentional effort during memory retrieval. Methods Whole-brain functional MRI was used to examine 8 subjects during retrieval in a block-designed fMRI experiment (Fig. 1). Two incidental study conditions were manipulated: Semantic and perceptual word encoding conditions. This manipulation of level of processing (LoP) was expected to yield two retrieval conditions that differed with regard to intentional retrieval effort and successful conscious recollection: Semantic encoding yielding low level of retrieval effort with high level of retrieval success and perceptual encoding yielding high level of effort with low level of retrieval success. After studying, word fragment completion (WFC) task was presented and then cued recall (CR) task was presented with word fragment cues. PER 30S SEM 30S 30S PER 30S 30S UNS PER SEM 30S SEM 30S 30S 30S UNS PER SEM 30S 30S 30S 30S 30S 30S 30S 30S 30S Fig. 1. A schematic illustration of study (above) and retrieval (below) paradigm. Critical study blocks (Semantic Encoding and Perceptual Encoding) were 30-s long separated by 30-s blocks of fixation (+). Critical retrieval blocks (Unstudied, Perceptually studied, Semantically studied) were also 30-s long separated by 30-s blocks of fixation in each of WFC and CR tasks. Results During explicit retrieval (CR) of the semantically encoded words, right inferior frontal regions (Brodman Areas 45, 47) were activated but right anterior frontal regions (BA 10) were deactivated. These results suggest different roles of different prefrontal regions during explicit (episodic) memory retrieval: BA 45/47 involved in conscious recollection and BA 10 in intentional effort (McIntosh et al., 1997). Also, parahippocampal gyrus was activated during explicit retrieval of the semantically encoded words, and this result supports the idea that medial temporal lobe is a neural correlate of conscious retrieval success. During implicit retrieval (WFC), occipital lobe (BA 17, 18 including fusiform gyrus) showed reduced activation when word fragments were primed, and this result supports the view that posterior areas are neural correlates of perceptual priming. Unexpectedly, right parahippocampal gyrus showed increased activation during implicit retrieval of the semantically encoded words. This result suggests that LoP effects which were often observed in studies of implicit memory retrieval could be the result of involuntary recollection (explicit contamination). Acknowledgements This research was supported as a Brain Neuroinformatics Research Program sponsored by Korean Ministry of Science and Technology. References McIntosh, A. R., Nyberg, L., Bookstein, F. L., & Tulving, E. (1997). Differential functional connectivity of prefrontal and medial temporal cortices during episodic memory retrieval. Human Brain Mapping, 5, 323-327. Schacter, D. L. (1987). Implicit memory: History and current status. Journal of Experimental Psychology: Learning, Memory, and Cognition, 13, 501-518. Schacter, D. L., & Buckner, R. L. (1998). On the relations among priming, conscious recollection, and intentional retrieval: Evidence from neuroimaging research. Neurobiology of Learning and Memory, 70, 284-303.

Implicit and explicit associative memory in patients with schizophrenia

Although patients with Alzheimer dementia (AD) have impaired explicit memory, more automatic, implicit aspects of learning and memory may be relatively preserved. However, neuropsychological tests for the assessment of implicit memory are lacking. This study examines a newly developed test, the Implicit Memory Test, in 28 patients with severe AD (mini-mental state examination 5 to 12) and 22 cognitively unimpaired matched controls (mini-mental state examination 25 to 29). The Implicit Memory Test consists of visually presented word (stem-completion) and picture (fragmented picture identification) subtests, each comprising 3 learning trials and a delayed test. Explicit memory was also assessed, using the verbal paired-associate learning subtest from the Wechsler Memory Scale and the Visual Association Test. Patients with AD obtained a floor performance on both explicit memory tests, whereas a significant learning curve was found for both the stem-completion and the fragmented pictures subtests of the Implicit Memory Test. Delayed testing on the fragmented pictures subtest showed a preserved performance that may have been mediated by implicit learning. Delayed performance on the stem-completion subtest, however, showed clear memory decay that suggests contamination by explicit memory function, at least in the controls. These findings extend the earlier results on word-stem completion and fragmented picture identification in patients with mild-to-moderate AD and indicate that residual learning capacity can be assessed in severe AD.

Explicit and implicit memory in the elderly: Evidence for double dissociation involving medial temporal- and frontal-lobe functions.

Four models were compared on repeated explicit memory (fragment cued recall) or implicit memory (fragment completion) tasks (Hayman & Tulving, 1989a). In the experiments, when given explicit instructions to complete fragments with words from a just-studied list-the explicit condition-people showed a dependence relation between the first and the second fragment targeted at the same word. However, when subjects were just told to complete the (primed) fragments-the implicit condition-stochastic independence between the two fragments resulted. Three distributed models-CHARM, a competitive-learning model, and a back-propagation model produced dependence, as in the explicit memory test. In contrast, a separate-trace model, MINERVA, showed independence, as in the implicit task. It was concluded that explicit memory is based on a highly interactive network that glues or binds together the features within the items, as do the first three models. The binding accounts for the dependence relation. Implicit memory appears to be based, instead, on separate non interacting traces.

Implicit tests of memory have become very popular. Age-related differences between young and older children typically observed on explicit memory tests are largely reduced with implicit memory testings. Yet to draw conclusions about the developmental invariance of priming from findings on one single type of implicit memory test seems problematic because of dissociations observed between different implicit tests. These dissociations have led researchers to classify memory tasks according to the forms of information they access or the type of processing they require. Developmental research has extensively demonstrated that existing semantic knowledge is a crucial factor in accounting for age-related differences in explicit memory performance. The conditions should be studied in which age-related differences can be observed as well as what kind of conceptual knowledge and conceptual processes are responsible for the differences.

Background and objectives: Implicit (unconscious) and explicit (conscious) memory associations with drugs have been examined primarily using verbal cues. However, drug seeking, drug use behaviors, and relapse in chronic cocaine and other drug users are frequently triggered by viewing substance-related visual cues in the environment. We thus examined implicit and explicit memory for drug picture cues to understand the relative extent to which conscious and unconscious memory facilitation of visual drug cues occurs during cocaine dependence. Methods: Memory for drug-related and neutral picture cues was assessed in 14 inpatient cocaine-dependent polydrug users and a comparison group of 21 young adults with limited drug experience (n = 35). Participants completed picture cue exposure, free recall and recognition tasks to assess explicit memory, and a repetition priming task to assess implicit memory. Results: Drug cues, compared to neutral cues, were better explicitly recalled and implicitly primed, and especially so in the cocaine group. In contrast, neutral cues were better explicitly recognized, and especially in the control group. Conclusion: Certain forms of explicit and implicit memory for drug cues were enhanced in cocaine users compared to controls when memory was tested a short time following cue exposure. Enhanced unconscious memory processing of drug cues in chronic cocaine users may be a behavioral manifestation of heightened drug cue salience that supports drug seeking and taking. There may be value in expanding intervention techniques to utilize cocaine users’ implicit memory system.

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.

Perceptual identification task points to continuity between implicit memory and recall

The author introduces implicit (versus explicit) memory to examine advertising effects on brand choice. Whereas explicit memory is demonstrated by the conscious recollection of an event, implicit memory is inferred by an improvement in some task performance as the result of having experienced the event. This research shows that memory-based choice benefits from advertising that enhances conceptually driven implicit memory whereas stimulus-based choice benefits from advertising that enhances perceptually driven implicit memory. The findings provide evidence that the two types of implicit memory and explicit memory are distinct constructs of memory; the findings also suggest that implicit memory measures may be more useful indicators of advertising effectiveness than explicit memory measures.