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Biomedical subjects

M Moscovitch

Publications and source records attributed to M Moscovitch.

At least 73 records · Page 4Linked to original sources
PubMed1996

Heightened interference on implicit, but not explicit, tests of negative transfer: evidence from patients with unilateral temporal lobe lesions and normal old people.

The present research investigated alternative explanations of heightened interference in AB-AC learning in individuals with memory loss related to medial temporal lobe dysfunction. In Experiment 1, patients with left or right temporal lobectomy and control subjects were administered the standard AB-AC test. Relative to the other groups, left temporal patients exhibited significant negative transfer that was characterized by large numbers of response intrusion errors. In Experiment 2, groups of community-dwelling old and young adults were administered the standard test and an implicit version in which, during AC testing, subjects were instructed to provide the first word that comes to mind in response to stimulus words. There were no differences between groups on either version. Of particular interest was that both groups made significantly more intrusion errors on the implicit test and did not differ on this measure. It was concluded that exaggerated interference in AB-AC learning, as reflected by response intrusion errors, is related to the use of implicit memory processes rather than a failure of inhibitory mechanisms. Memory-impaired individuals, who have a selective loss of explicit memory, are vulnerable on this task because they rely excessively on implicit memory processes.

Adolescent↗
PubMed1996

The effect of imagery on explicit and implicit tests of memory in young and old people: a double dissociation.

The use of imagery as an elaborative study task was examined to determine its effects on implicit and explicit tests of memory in both young and old adults. Both the implicit and explicit tests were word-stem completion tests, identical except for their instructional content. Results showed that imaging the referent of a visually-presented word during the initial study period significantly improved the performance of the young adults on the explicit test of memory, but reduced their performance on the implicit test. The test results of the elderly subjects showed a similar trend in that explicit test performance was significantly improved following an imagery study task whereas implicit test performance was reduced following this same task. These results did not, however, reach the level of significance, observed for young adults. The results are discussed within the framework of a processing account of implicit/explicit dissociations.

Adult↗
PubMed1995

Dissociation of pathways for object and spatial vision: a PET study in humans.

A positron emission tomography (PET) study was conducted to determine which brain regions are differentially involved in visual object identification and object localization. Subjects engaged in a spatial task in which they matched the location of common objects, and an object task in which they matched the identity of common objects. In both tasks the stimulus arrangements used were of the same kind. Regional cerebral blood flow data showed that a right-sided region in the inferior parietal lobule was more activated during spatial than during object matching. In contrast, bilateral occipitotemporal regions, with the left more predominant, were more activated during object than spatial matching. These results provide support for Ungerleider and Mishkin's dual pathway model of vision and indicate important patterns of lateralization in the human visual system.

Brain↗
PubMed1995

The contribution of external and internal features to the matching of unfamiliar faces.

The relative efficacy of external and internal features in matching unfamiliar faces was studied in three experiments in which the subjects matched target and test faces differing in terms of external or internal features, or both. In Experiment 1 only full congruency between target and test faces was considered a match; in Experiments 2 and 3 faces sharing the same external and internal features were also considered to be matches. A total of 100 subjects matched 192 pairs of target and test faces in a "same-different" task. Reaction times and matching errors were recorded for analyses of variance. In all three experiments performance was best when either all features matched or all features mismatched, with mismatches having a slight edge. When matches of external and internal features with the target faces were inconsistent with each other, mismatches of external features led to faster responses in Experiments 1 and 2, and mismatches of internal features led to faster responses in Experiment 3. The results suggest that since faces are configurational stimuli, face matching is influenced by the non-relevant set of features; and that mismatches, especially of external features, influence face matching more than matches do.

Face↗
PubMed1995

Repetition priming for newly formed and preexisting associations: perceptual and conceptual influences.

Three experiments demonstrate that association-specific repetition effects can be obtained for both newly formed and preexisting associations and that these effects are sensitive to modality of presentation. After studying a list of word pairs, participants were shown the original intact pairs and pairs formed by recombining the original pairs. In a lexical-decision task in which participants were asked to indicate whether both items were words, responses were faster to newly formed associations in the intact than in the recombined condition. This association-specific repetition priming effect was also observed for preexisting associations when a speeded relatedness judgment task was used. Both effects were found to be attenuated under cross-modal presentation. Finally, an explicit speeded recognition task revealed an associative effect that was not attenuated when modality was crossed for newly formed associations and was actually exaggerated for preexisting associations, suggesting that the repetition priming effects were not produced by conscious recollection. Results are discussed in terms of frameworks that are based either on perceptual representation systems or on a transfer-appropriate processing model.

Adult↗
PubMed1995

Repetition priming effects for newly formed associations are perceptually based: evidence from shallow encoding and format specificity.

This article is concerned with memory for newly formed associations as displayed on implicit and explicit tests of memory. After studying a list of word pairs, participants were shown the original intact pairs and pairs formed by recombining the original pairs. Pairs were simultaneously presented both at study and at test. In a lexical-decision task in which participants were asked to indicate whether both items were words, responses to intact pairs were faster than to recombined pairs. The size of this association-specific repetition effect was relatively unaffected by a levels-of-processing manipulation, indicating that conceptual processes did not likely contribute to the production of the effect. Furthermore, the effect was not produced when pairs were presented simultaneously at study but sequentially at test, thus highlighting the importance of format of presentation. Finally, in an explicit speeded-recognition task the size of the association-specific effect was largely affected by levels-of-processing manipulation and was revealed even under sequential test presentation suggesting that the associative repetition effects were not contaminated by conscious recollection. Together, the results show that perceptual factors are involved in both storage and retrieval of associative information in data-driven implicit tests of memory.

Adult↗
PubMed1995

Recovered consciousness: a hypothesis concerning modularity and episodic memory.

Why should conscious recollection be associated with recovery of some memories and not others? A hypothesis is proposed and defended that the medial temporal lobe/hippocampal complex (MTL/H) and related limbic structures comprise a memory module that receives as its input only information that is consciously apprehended. The module then binds or conjoins into memory traces those neural elements that mediated the conscious experience so that effectively "consciousness" is as intergral a part of the memory traces as it was during the experience of the event. When memory traces are retrieved, what is recovered are the phenomenological records (Conway, 1992) of experienced events which are integrated content-consciousness packets. Evidence is presented which suggests that the MTL/H module satisfies Fodorian criteria of modularity. The MTL/H module is compared to perceptual modules in nonfrontal neocortex that mediate performance on tests of memory without awareness and to prefrontal neocortex that acts as a central working-with-memory system that operates on the input to MTL/H and the shallow output from it.

Animals↗
PubMed1994

Hemispheric encoding/retrieval asymmetry in episodic memory: positron emission tomography findings.

Data are reviewed from positron emission tomography studies of encoding and retrieval processes in episodic memory. These data suggest a hemispheric encoding/retrieval asymmetry model of prefrontal involvement in encoding and retrieval of episodic memory. According to this model, the left and right prefrontal lobes are part of an extensive neuronal network that subserves episodic remembering, but the two prefrontal hemispheres play different roles. Left prefrontal cortical regions are differentially more involved in retrieval of information from semantic memory and in simultaneously encoding novel aspects of the retrieved information into episodic memory. Right prefrontal cortical regions, on the other hand, are differentially more involved in episodic memory retrieval.

Brain↗
PubMed1994

Intact visual imagery and impaired visual perception in a patient with visual agnosia.

Although it is now well accepted that visual mental imagery and visual perception share common underlying mechanisms, there are several reports in which they are dissociated. Evidence for the separability of these processes is provided by a patient, C.K., who has a profound visual object recognition deficit attributable to an impairment in grouping or segmenting visual images. Despite this perceptual deficit, C.K. was able to draw objects in considerable detail from memory, and his knowledge of the visual appearance of objects was preserved on a variety of mental imagery tasks. Together with previous cases, these findings confirm the double dissociation between object recognition and perception. Interestingly, C.K. could also recognize newly constructed objects in his internal imagery. To accommodate these results, we propose a model in which imagery and perception are strongly associated but are also functionally specialized.

Adult↗
PubMed1994

Contributions of surface and conceptual information to performance on implicit and explicit memory tasks.

Four experiments examined the effects of perceptual and conceptual processing operations on 2 implicit and 2 explicit memory tasks. Results show an advantage of visual over auditory presentation for word-fragment completion, word-stem completion, and word-stem cued recall; there was no such advantage in recognition memory. Conceptual processing had no effect on the implicit tasks, a small effect on word-stem cued recall, and a large effect on recognition. It is concluded that there is no necessary trade-off between the 2 types of information. Speculatively, the use of perceptual information may be all or none and relatively automatic, whereas the use of conceptual information appears to be graded and more under conscious control.

Acoustic Stimulation↗
PubMed1994

Intact primary memory in mild to moderate Alzheimer disease: indices from the California Verbal Learning Test.

The California Verbal Learning Test (CVLT; Delis, Kramer, Kaplan, & Ober, 1987) was administered to patients with mild to moderate Alzheimer disease (AD) (Group AD; n = 13) and to a control group of normal older adults (Group NC; n = 13) matched on age and education. Two measures were used to determine whether primary memory (PM) is impaired in early AD. One measure, considered a relatively "pure" measure of PM, is based on the procedure developed by Tulving and Colotla (1970) which considers an item to be recalled from PM if no more than six items intervene between its presentation and recall. The other measure is the more commonly used recall from recency. No significant difference between the AD and NC Groups was found, both on the Tulving and Colotla measure, as well as on the recall from recency measure of PM. A significant difference was obtained on two measures of secondary memory (SM), namely, Tulving and Colotla's measure and recall from the primacy and middle regions of the list of words. In comparison to NC, and AD patients showed little evidence of learning over the five trials, and poor retention even over short delays. In addition, the patients with AD showed deficits in clustering words by taxonomic category at recall. We conclude that impairment in PM cannot be used as a diagnostic marker of AD in the early stages of the disease process.

Aged↗
PubMed1992

Dissociation between mental imagery and object recognition in a brain-damaged patient.

Visual imagery is the creation of mental representations that share many features with veridical visual percepts. Studies of normal and brain-damaged people reinforce the view that visual imagery and visual perception are mediated by a common neural substrate and activate the same representations. Thus, brain-damaged patients with intact vision who have an impairment in perception should have impaired visual imagery. Here we present evidence to the contrary from a patient with severely impaired object recognition (visual object agnosia) but with normal mental imagery. He draws objects in considerable detail from memory and uses information derived from mental images in a variety of tasks. In contrast, he cannot identify visually presented objects, even those he has drawn himself. He has normal visual acuity and intact perception of equally complex material in other domains. We conclude that rich internal representations can be activated to support visual imagery even when they cannot support visually mediated perception of objects.

Adult↗
PubMed1992

Memory with and without awareness: performance and electrophysiological evidence of savings.

Event-related potentials (ERPs) recorded on the scalp were shown to be sensitive indicators of the strength of a memory trace on both implicit and explicit tests of memory. In explicit recognition tests, the amplitude of a positive potential identified as P300 was larger for "old" than for "new" words regardless of whether the subject categorized the items correctly. This effect, however, was statistically reliable only when the recognition memory (d') was relatively high. In contrast to ERPs, the reaction times in explicit recognition were sensitive to accuracy but not to repetition. In implicit tests, lexical decisions to repeated words were faster than to newly presented words. The magnitude of the repetition effect varied neither with elapsed time since the last repetition nor with the number of previous repetitions. In contrast, the P300 elicited by the same words were sensitive to both lag and recency of repetition, suggesting that they were influenced by the episodic memory strength of the items.

Adult↗
PubMed1990

Memory for temporal order and conditional associative-learning in patients with Parkinson's disease.

The performance of Parkinson's patients was compared to that of normal controls on memory for temporal order and conditional associative-learning tasks, each of which is sensitive to frontal-lobe dysfunction. Memory for temporal order involved reconstructing the presentation order of each of a series of drawings, words and designs. Recognition of similar stimuli was also examined. Parkinson's patients exhibited poor memory for the relative temporal relations between stimuli, though no group differences were observed in the number of stimuli placed in the correct position. Recognition was intact in the Parkinson's patients, and an absence of correlation between performance on the recognition and temporal order tasks indicates that the poor memory for temporal order is not simply a function of degraded memory for the individual stimuli. The conditional associative-learning task required subjects to learn, either by trial-and-error or with immediate correction, numbers paired with drawings, designs or spatial locations. Parkinson's patients were impaired only when learning by trial-and-error was required. Results suggest that the strategic retrieval processes involved in both memory for temporal order and learning conditional associations by trial-and-error depend on the integrity of the fronto-striatal system, which is known to be affected in Parkinson's disease.

Aged↗
PubMed1990

Hemispheric control of spatial attention.

According to the activation-orienting hypothesis the distribution of attention in space is biased in the direction contralateral to the more activated hemisphere. The present investigation tested this proposal and evaluated the nature of hemispheric differences in orienting control. Activation imbalance was produced by a unilateral visual stimulus. The distribution of attention was measured using a modified line bisection task in which subjects judged the location of an intersect on a tachistoscopically presented horizontal line. The first three experiments suggest that (a) attention is biased in the direction contralateral to the stimulated hemisphere, and (b) the biases do not depend on the task relevance or hemispatial position of the stimulus producing the activation imbalance. The final three experiments suggest that when orienting conflict is introduced the rightward bias becomes more robust than the leftward bias. The findings are consistent with the activation-orienting hypothesis. Each hemisphere generates a contralateral attentional bias and the rightward bias of the left hemisphere is stronger. The relevance of these findings to understanding unilateral neglect resulting from parietal damage is discussed.

Adult↗