Implicit Retrieval Research Articles

Neural Mechanism of Implicit and Explicit Memory Retrieval: Functional MR Imaging

Purpose: To identify, using functional MR imaging, distinct cerebral centers and to evaluate the neural mechanism associated with implicit and explicit retrieval of words during conceptual processing. Materials and Methods: Seven healthy volunteers aged 21-25 (mean, 22) years underwent BOLD-based fMR imaging using a 1.5T Signa Horizon Echospeed MR system. To activate the cerebral cortices, a series of tasks was performed as follows: the encoding of two-syllable words, and implicit and explicit retrieval of previously learned words during conceptual processing. The activation paradigm consisted of a cycle of alternating periods of 30 seconds of stimulation and 30 seconds of rest. Stimulation was accomplished by encoding eight twosyllable words and the retrieval of previously presented words, while the control condition was a white screen with a small fixed cross. During the tasks we acquired ten slices (6 mm slice thickness, 1 mm gap) parallel to the AC-PC line, and the resulting functional activation maps were reconstructed using a statistical parametric mapping program (SPM 99). Results: A comparison of activation ratios (percentages), based on the number of volunteers, showed that activation of Rhs-35, PoCiG-23 and ICiG-2630 was associated with explicit retrieval only; other brain areas were activated during the performance of both implicit and explicit retrieval tasks. Activation ratios were higher for explicit tasks than for implicit; in the cingulate gyrus and temporal lobe they were 30% and 10% greater, respectively. During explicit retrieval, a distinct brain activation index (percentage) was seen in the temporal, parietal, and occipital lobe and cingulate gyrus, and PrCeG-4, Pr/PoCeG-43 in the frontal lobe. During implicit retrieval, on the other hand, activity was greater in the frontal lobe, including the areas of SCA-25, SFG/MFG-10, IFG-4445, OrbG-1147, SFG-68, and MFG-946. Overall, activation was lateralized mainly in the left hemisphere during both implicit and explicit retrieval tasks. For explicit retrieval, the lateralization index was more than twice as high as for implicit retrieval. Conclusion: Our findings indicate that there is neuro-anatomical dissociation between implicit and explicit retrieval of words during conceptual processing, suggesting, on the basis of cognitive neuroscience, that the performance of implicit and explicit memory-related tasks involves different mechanisms.

Implicit and Explicit Alcohol‐Related Cognitions

This article presents the proceedings of a symposium at the 2001 RSA Meeting in Montreal, Canada organized by Reinout W. Wiers and Alan W. Stacy. The purpose of the symposium was to present recent applications of implicit cognitive processing theory to alcohol research. Basic cognitive research has demonstrated that implicit cognition influences memory and behavior without explicit recall or introspection. The presentations from this symposium show that implicit cognition approaches yield new insights into understanding drinking motivation. The presentations were: (1) An introduction by Alan W. Stacy; (2) Implicit cognition and alcohol use. Involvement of other variables? (Susan L. Ames); (3) Alcohol expectancies and the art of implicit priming (Jane A. Noll); (4) Parental alcoholism and the effects of alcohol on semantic priming (Michael A. Sayette); (5) Implicit arousal and explicit liking of alcohol in heavy drinkers (Reinout W. Wiers); and (6) Negative affective cues and associative cognition in problem drinkers (Martin Zack). Comments were provided by the discussant Marvin Krank. The presented studies demonstrated that: (1) implicit memories of alcohol associations are powerful predictors and cross-sectional correlates of alcohol use; (2) implicit retrieval processes influence alcohol outcome expectancies and alcohol consumption; (3) alcohol consumption influences implicit memory processing; (4) heavy drinkers reveal different affective responses in implicit and explicit tasks; and (5) negative affect exerts an implicit priming effect for alcohol associations in problem drinkers. These findings illustrate the importance of implicit cognition in understanding alcohol abuse and demonstrate the potential of the theoretical framework for more widespread application across a variety of areas of alcohol research, including diagnostics for the risk of alcohol abuse, treatment, and prevention.

Implicit False Memory: Effects of Modality and Multiple Study Presentations on Long-Lived Semantic Priming

In the Deese paradigm, studying a list of semantic associates (holiday, beach, etc.) produces false explicit memory for a nonpresented lure (vacation). Here, we examine false memory with implicit retrieval. Experiment 1 tested memory for lures and matched on-list targets, using stem completion (implicit) and stem-cued recall (explicit). We replicated McDermott's (1997) finding of implicit false memory at a 10-min delay, using better controls for explicit contamination. In Experiment 2, we show that this semantic priming is modality-specific (on the visual test, lure priming was reduced with auditory study of the semantic associates), consistent with the perceptual nature of stem completion. In Experiment 3, additional study presentations reduced false memory with explicit, but not implicit, retrieval, consistent with suppression of gist-based responses by veridical information only when explicit retrieval is required. Results also dissociate implicit and explicit false memory and demonstrate similarities between false and true memories with implicit retrieval.

Memory, consciousness and neuroimaging.

Neuroimaging techniques that allow the assessment of memory performance in healthy human volunteers while simultaneously obtaining measurements of brain activity in vivo may offer new information on the neural correlates of particular forms of memory retrieval and their association with consciousness and intention. We consider evidence from studies with positron emission tomography and functional magnetic resonance imaging indicating that priming, a form of implicit retrieval, is associated with decreased activity in various cortical regions. We also consider evidence concerning the question of whether two components of explicit retrieval--intentional or effortful search and successful conscious recollection--are preferentially associated with increased activity in prefrontal and medial temporal regions, respectively. Last, we consider recent efforts to probe the relation between the phenomenological character of remembering and neural activity. In this instance we broaden our scope to include studies employing event-related potentials and consider evidence concerning the neural correlates of qualitatively different forms of memory, including memory that is specifically associated with a sense of self, and the recollection of particular temporal or perceptual features that might contribute to a rich and vivid experience of the past.

On the Relations among Priming, Conscious Recollection, and Intentional Retrieval: Evidence from Neuroimaging Research

Neurobiological distinctions among forms of memory have been investigated mainly from the perspective of lesion studies in nonhuman animals and experiments with human neurological patients. We consider recent neuroimaging studies of healthy human volunteers using positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) that provide new information concerning the neural correlates of particular forms of memory retrieval. More specifically, we consider evidence indicating that priming, a form of implicit retrieval, is associated with decreased activity in various cortical regions. We also consider evidence suggesting that two components of explicit retrieval—intentional or effortful search and successful conscious recollection—are preferentially associated with increased activity in prefrontal and medial temporal regions, respectively.

Associative Priming in Word Fragment Completion: A Dissociation Between Explicit and Implicit Retrieval Processes

Three experiments investigated associative priming in word fragment completion. In associative priming, the study word that acts as a prime is semantically related in some way to the response word that the subject must produce or respond to at test. For example, a prime might be semantically related to the solution to its paired word fragment (e.g. study “VANILLA”, solve fragment “-H-C—A-E” at test, solution is “CHOCOLATE”). Associative priming therefore differs from both repetition and conceptual priming, in which the studied primes are themselves the words that must be produced or responded to at test. In Experiment 1, associative primes were found to influence word fragment completion performance on an explicit test, but not on an implicit test. Experiment 2 demonstrated that the effects of associative primes on explicitly instructed fragment completion cannot be attributed to the specific information about cue-prime relationships that is included in the explicit instructions. Experiment 3 demonstrated that a manipulation of modality, a variable known to disrupt implicit retrieval processes, disrupts repetition priming on an explicit test, but not associative priming. The results of these three experiments suggest that whereas repetition primes are retrieved from memory by both explicit and implicit retrieval processes, associative primes are retrieved by only explicit processes. These data suggest that implicit retrieval processes are cue-dependent processes which automatically retrieve memory information that provides a good match to retrieval cues. Explicit retrieval processes are cue-independent, functioning as an intentional retrieval set to access particular categories or types of memory information.

Time Course of Cortical Activations in Implicit and Explicit Recall

The distinction between implicit and explicit retrieval of learned material is central to recent thinking about the neural systems underlying memory. Word stem completion is one task in which subjects can be instructed either to make a deliberate recall (explicit instruction) or to be told to complete the stem with any appropriate word (implicit instruction). Positron emission tomography (PET) studies have indicated that during implicit retrieval, there is reduced blood flow in right posterior areas, whereas some tasks of explicit retrieval involve frontal and hippocampal activation. However, there is no information about the timing of these activations or how implicit and explicit retrieval might be related. We used word stem completion tasks similar to those used in the PET studies, but used high-density electrical recording designed to allow localization of the regions involved in the tasks and to provide temporal information. We found reduced activity for primed words in right posterior cortex corresponding to previous PET results. The reduction occurred within the first 200 msec after input, suggesting early interaction with the information stored in this area. Similar reductions observed during explicit recall of the previously presented words indicate that priming is similar under implicit and explicit conditions. In addition, when priming was not an adequate basis for response, then frontal areas were active. Retrieval of unprimed words under implicit instruction elicited right frontal activation, whereas explicit retrieval activated frontal areas bilaterally. Left frontal and hippocampal activations appear to occur only when the retrieval involved use of the words from the list studied previously.

ERPs during study as a function of subsequent direct and indirect memory testing in young and old adults

Event-related potentials (ERPs) were recorded from young and older adults while words were studied during structural and semantic encoding tasks. Items were presented twice to assess repetition effects. Subsequent memory effects (i.e. Dm or difference in subsequent memory) associated with non-target study items were also evaluated. Memory for non-target study items was tested either indirectly (word stem completion) or directly (cued recall). There were small, but unreliable age differences (favoring the young) on both the indirect and direct tests. These small differences were consistent with previous results for stem completion performance, but were counter to expectation for the cued recall test, where young adults were expected to show clear superiority. We conclude, based on task considerations, that for cued recall, subjects may have adopted an ‘implicit’ retrieval strategy. Because older adults typically have little difficulty with implicit retrieval, they fared almost as well as the young on cued recall. Dm effects were reliable for the young only. As Dm is thought to reflect elaborative encoding processes, the larger Dm magnitudes in the young than the old suggest that the small, though unreliable, age-related performance differences that resulted may have been mediated by such elaborative processing on the part of the younger adults.

Collaboration and Memory: Effects of Dyadic Retrieval on Different Memory Tasks

Collaborative retrieval was investigated in two experiments. The experiments were explicitly designed to investigate how different types of memory tasks were affected by two individuals working together compared to individuals working on their own. A nominal group score was treated as the predicted potential a dyad could attain. In Experiment 1, semantic and episodic retrieval were employed. The episodic task was to encode and retrieve a story and the semantic task was to answer, without any encoding, 20 questions from the same history domain as the episodic task. In Experiment 2, explicit recognition and implicit retrieval of dot patterns were employed. The explicit recognition task was forced-choice, and in the implicit task, subjects were instructed to complete a pattern they saw from an incomplete pattern. The results suggest that: (1) dyads suffer from collaboration relative to the predicted potential, (2) the reduction of productivity for dyads was limited to explicit and episodic memory tasks, and (3) friends as opposed to non-friends reduced the negative effect of collaboration. The results replicate and extend the results from a previous study.

Implicit and explicit memory retrieval within and across the disconnected cerebral hemispheres.

Implicit and explicit memory retrieval within and across the disconnected cerebral hemispheres.

Psychopharmacological analysis of implicit and explicit memory: a study with lorazepam and the benzodiazepine antagonist flumazenil

Recent studies have suggested that the benzodiazepine (BZ) lorazepam (LZ) differs from other BZs in its impairing effects on implicit memory tasks. The present study was designed to assess whether this atypical effect withstood the experimental rigour of Schacter's retrieval intentionality criterion and further, whether it could be reversed by the BZ antagonist, flumazenil (FL). The separate and combined effects of LZ, FL and placebo (PL) were assessed on indices of memory, sedation, and attention in 48 healthy volunteers. LZ disrupted performance on both explicit and implicit memory tasks, induced motor sedation and impaired focussed attention. Fl attenuated LZ-induced attentional deficits but did not affect motor sedation. FL also attenuated LZ-induced impairment on the implicit retrieval task. On the explicit retrieval task FL attenuated LZ-induced impairment for words which had been deeply processed at study but not words which had been shallowly processed. A subsequent recognition test showed LZ impaired recognition memory only when accompanied by recollective experience and flumazenil again attenuated this effect. FL itself lowered performance on several measures, reflecting intrinsic activity of this "antagonist". Assessment of the relationship between the mnestic and other effects of the drugs suggested that attentional effects contribute to, but do not explain, effects on implicit memory tasks. These results imply that the apparent atypical effects of LZ on implicit memory tasks are mediated by the same BZ receptor complex as mediates LZ's other effects.

Implicit retrieval processes in cued recall: Implications for aging effects in memory

Aging produces deficits in what has come to be called explicit or direct memory, in which subjects must consciously retrieve information from long-term memory. In contrast, many studies have shown that when implicit or indirect memory is tested, old and young subjects perform equivalently. The present study manipulated orienting instructions (structural vs. semantic) for indirect (stem completion) and direct (cued recall) memory tasks for both young and old subjects. Contrary to previous research, older subjects produced equivalent performance to young subjects on the direct test as well as on the indirect test, and performance of both groups was worse in the direct than indirect test. In addition, semantic orienting activity at study led to greater learning on the indirect test than structural orienting for both groups, although the levels of processing effect was greater for the direct test. We attribute the unexpected lack of age difference on the direct test to its difficulty, which led subjects to adopt an implicit (generate + recognize) rather than an explicit retrieval strategy during the cued recall task. Because the elderly are not impaired with regard to either implicit retrieval or recognition, this strategy produced equivalent performance in the two groups.

Infectious endophthalmitis after cataract surgery.

The distinction between implicit and explicit retrieval of learned material is central to recent thinking about the neural systems underlying memory. Word stem completion is one task in which subjects can be instructed either to make a deliberate recall (explicit instruction) or to be told to complete the stem with any appropriate word (implicit instruction). Positron emission tomography (PET) studies have indicated that during implicit retrieval, there is reduced blood flow in right posterior areas, whereas some tasks of explicit retrieval involve frontal and hippocampal activation. However, there is no information about the timing of these activations or how implicit and explicit retrieval might be related. We used word stem completion tasks similar to those used in the PET studies, but used high-density electrical recording designed to allow localization of the regions involved in the tasks and to provide temporal information. We found reduced activity for primed words in right posterior cortex corresponding to previous PET results. The reduction occurred within the first 200 msec after input, suggesting early interaction with the information stored in this area. Similar reductions observed during explicit recall of the previously presented words indicate that priming is similar under implicit and explicit conditions. In addition, when priming was not an adequate basis for response, then frontal areas were active. Retrieval of unprimed words under implicit instruction elicited right frontal activation, whereas explicit retrieval activated frontal areas bilaterally. Left frontal and hippocampal activations appear to occur only when the retrieval involved use of the words from the list studied previously.

System Noise in the NESDIS TOVS Forward Model. Part II: Consequences

Abstract To utilize satellite radiance sounding data, in either explicit or implicit retrieval algorithms, a proper understanding of the noise in the measurements is required. Conventionally, to define the expected accuracy of atmospheric profiles inferred from sounder data, instrument noise equivalent temperature difference (NEΔT) noise specifications have been used to simulate spacecraft data. Here it is demonstrated that NEΔT noise specifications are inappropriate for this purpose. Instead, total system noise estimates should be employed since use of sounding data in any type of physical retrieval algorithm implies application of a radiative transfer model, which in turn must be “calibrated” against in situ and satellite data. It is demonstrated that the accuracy of atmospheric retrievals inferred from the TIROS Operational Vertical Sounder radiometers is limited by the total system noise rather than NEΔT noise, and that modeled radiance temperatures perturbed by Gaussian total system noise very nearly...

Implicit and Explicit Memory in Patients With Parkinson's Disease With and Without Dementia

To study explicit and implicit memory processes in patients with Parkinson's disease. Case-control design. All subjects were given a neuropsychological test battery, and the test scores were compared among the groups. Government-funded research facility. All subjects were examined as outpatients. We tested nondemented (n = 13) and demented (n = 5) patients with Parkinson's disease and normal controls (n = 12) matched for age, gender, and educational level. Memory for verbal and pictorial stimuli under both explicit and implicit retrieval conditions. Both nondemented and demented patients with Parkinson's disease exhibited impairment on tests of explicit memory. Their impairment could be graded based on the level of effort required by the task: impaired free recall in nondemented patients and impaired free recall, cued recall, and recognition in demented patients. By contrast, neither group showed evidence of impairment on automatic (modality monitoring and word frequency estimation) or implicit (word and picture fragment identification) memory tasks. Correlation analyses did not support any association between the effortful memory deficits and neurologic variables, mood, or performance on executive function tests. Memory deficits in patients with Parkinson's disease primarily involve the conscious, effortful strategic aspects of searching long-term memory.

Negative priming in a spatial localization task: Feature mismatching and distractor inhibition.

Negative priming has recently been demonstrated in tasks requiring spatial localization (S. P. Tipper, J. C. Brehaut, & J. Driver, 1990), supporting the notion that distractors are actively inhibited during selection. However, it has since been argued that this effect is caused by the appearance of mismatching identities at a single location (J. Park & N. Kanwisher, 1994). The present studies show that negative priming in a spatial localization task can occur when the ignored distractor and subsequent target are identical. However, feature mismatches can also lead to negative priming. The argument is made that distractor inhibition and implicit retrieval of previously presented items together provide a better account of efficient sequential selective behavior than does either process alone. Consider a bartender clearing glasses from a table. This apparently simple perceptual-motor interaction can be broken down into two complex stages of processing. The first stage encompasses the movement of the hand toward one glass among others in the same path of motion, and thus affords conflicting motor responses (see Tipper, Lortie, & Baylis, 1992). The second stage encompasses subsequent motor behavior after action toward the first glass has been completed. This second stage of processing is the focus of the present article. However, a complete understanding of how action is directed toward an object that was ignored in a recent perceptual-motor interaction begins with an understanding of the processing consequences of originally ignoring that object. Two mechanisms have been proposed to explain how action can be selectively directed toward one object when there are distracting objects in the scene. Most early models of selective attention proposed that internal representations of the attended object receive analysis beyond that of initial perceptual processing. This extra level of excitation was considered sufficient to separate the target from distractor (Broadbent, 1958, 1982; Van der Heijden, 1981). More recently, inhibitory mechanisms have been proposed to play a role complementary to that of excitation in separating

Stochastic independence in the recognition/identification paradigm

Abstract Experiments in which subjects study a set of items and then take two successive tests, a recognition test followed by a test of implicit retrieval of the same items (e.g. Tulving, Schacter, & Stark, 1982), have typically yielded data showing stochastic independence between the tests. Ostergaard (1992) has suggested that the procedure for assessing such independence should include an evaluation of the data against a model that assumes maximal dependence between the components of the test attributable to the study episode. In applying his Maximum Memory Dependence model to the published data, however, Ostergaard inexplicably used test-primed data for baseline measures, rather than non-primed data, and erroneously concluded that there was no clear evidence for independence. In this article, we show that when the standard baseline measures are used, the results of many experiments demonstrate stochastic independence.

Perceptual and conceptual cueing in implicit and explicit retrieval

Subjects saw or heard words in a list (e.g. limerick) and then took two successive tests. The first was a yes/no recognition test in which auditory/visual modality of test words was manipulated orthogonally to the study modality. The second test varied with experimental conditions: subjects produced words to either perceptual (fragment) cues (l- -e-ick) or conceptual cues (What name is given to a lighthearted five-line poem?), under either explicit or implicit retrieval instructions. The major findings were: (a) that regardless of the type of retrieval cue (perceptual or conceptual) the degree of dependency between recognition and cued recall was greater than that between recognition and implicit retrieval; and (b) that modality shifts adversely affected perceptually cued explicit and implicit retrieval, whereas they had no effect either on conceptually cued retrieval or on recognition. These results suggest that the memory system subserving, and the processes involved in, conceptual priming differ from those underlying recognition and perceptual priming.

Implicit information retrieval

In an information retrieval system, many queries depend upon the realization of information implicit in the information base for a satisfactory response. Such problems as the recognition of morphological variation in language, the detection of word or sentence synonymy in context and the determination of simple logical or causal consequences of the information base, all depend to a lesser or greater extent upon information not explicitly available by currently used techniques. We describe-an experimental model for the exploration of “implicit retrieval”. Simple English text is mapped into a formalism suitable for machine inference. The performance of the model will be illustrated with extracts from the Wall Street Journal. Future application of the principles of implicit retrieval to conventional retrieval systems will be briefly discussed.