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Biomedical subjects

M Moscovitch

Publications and source records attributed to M Moscovitch.

At least 19 recordsLinked to original sources
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↗
PubMed1990

Hippocampal and prefrontal cortex contributions to learning and memory: analysis of lesion and aging effects on maze learning in rats.

Young adult rats with bilateral lesions to the hippocampus or prefrontal cortex, young operated controls, and normal old rats were tested on two complex mazes in the Hebb-Williams series. Approximately half the animals were previously trained on one of the mazes; the remainder received no previous training. The trained hippocampal rats showed sparing of memory for the general skill of maze learning but poor recall of the specific maze on which they had been previously trained. The opposite pattern was observed in trained prefrontal rats. In contrast, the aged rats' memory for maze-specific and maze-general information was impaired. The results confirmed the importance of the hippocampus for recalling highly specific information and pointed to a possible role for the frontal lobes in learning and remembering nonspecific skill-related information. The generalized deficit of the aged rats indicates that both types of memory were compromised and offers further evidence of frontal lobe and hippocampal dysfunction in normal aging.

Aging↗
PubMed1990

A comparison of cognitive function in community-dwelling and institutionalized old people of normal intelligence.

Two carefully matched groups of normal old people living in institutions or in the community were administered a neuropsychological cognitive test battery. In general, the institutionalized group performed worse than the community group. Discriminant function analysis identified a subgroup of high-functioning institutionalized subjects whose performance more closely resembled that of the community group than the remainder of the institutionalized group. Differences between the various groups were not due to differences in IQ, age, health, or other controlled variables. The critical tests that differentiated the groups were sensitive to impaired function in frontal and medial-temporal lobe brain regions. The results suggest a complex interaction involving effects of age and environmental factors on brain function and cognition.

Aged↗
PubMed1990

Perceptual and conceptual mechanisms in neglect dyslexia. Two contrasting case studies.

The contribution of peripheral, data-driven effects is contrasted with conceptual, 'top-down' effects to the reading performance of 2 subjects with neglect dyslexia following a single right hemisphere lesion. Several tasks were administered, manipulating the physical, lexical or morphemic properties of the stimuli in an attempt to establish whether the attentional deficit disrupts reading at an early or late stage of processing. Both subjects were impaired at detecting elementary stimulus features on the left side of the display but were even more impaired at identifying conjoined features. One subject's performance was influenced by structural manipulations which altered the low-level representation of the stimulus. The other was less affected by structural changes of the stimuli but was influenced by the lexical and morphemic status of the words. This apparent double dissociation is interpreted as arising from a graded attentional deficit at a single locus, early in the reading process where low-level information is detected. When the deficit is not severe sufficient information may be picked up and may interact with higher order lexical knowledge to offset partially the peripheral malfunction. For a severe attentional deficit, top-down knowledge is not engaged as insufficient information is processed on the left-hand side. This hybrid view of attention provides insight into the mechanisms underlying neglect dyslexia and bears on the role of attention in normal visual processing.

Aged↗
PubMed1988

Priming of semantic autobiographical knowledge: a case study of retrograde amnesia.

The case of a 36-year-old man who suffers dense retrograde and anterograde amnesia as a result of closed-head injury that caused extensive damage to his left frontal-parietal and right parieto-occipital lobes is described. Patient K.C. has normal intelligence and relatively well-preserved perceptual, linguistic, short-term memory, and reasoning abilities. He possesses some fragmentary general knowledge about his autobiographical past, but he does not remember a single personal event or happening from any time of his life. He has some preserved expert knowledge related to the work he did for 3 years before the onset of amnesia, although he has no personal recollections from that period. Some features of K.C.'s retrograde amnesia can be interpreted in terms of the distinction between episodic and semantic memory, and in terms of the distinction between episodic and semantic autobiographical knowledge. K.C.'s semantic knowledge, but not his episodic knowledge, showed progressive improvement, or priming, in the course of the investigation.

Adult↗
PubMed1988

The time course of repetition effects for words and unfamiliar faces.

The repetition effect on reaction time to words and unfamiliar faces was examined at lags of 0, 4, and 15 items between first and second presentations. For words, subjects made either a lexical decision or a decision based on the stimulus's structural attributes. In the lexical decision task, a significant repetition effect was found at all three lags for words, whereas for nonwords the effect was significant only at Lag 0. In the structural decision task, the repeated decision was facilitated for both words and nonwords only at Lag 0, despite a word superiority effect at all lags. Target faces were presented either zero, one, or five times before testing. Subjects made either structural discriminations (face/nonface) or recognition judgments. In the structural discrimination task, the effect of repetition was significant only at Lag 0 (regardless of the number of pretest presentations). In the recognition task, the repetition effect was longer lasting, and its magnitude increased with the number of presentations which, presumably, determined the strength of the episodic memory trace. These results are taken as showing that repetition effects, like other measures of memory, are influenced by the type of stimulus, its preexperimental history, the level to which it is processed, and the lag between the initial presentation and the test. The manner in which these variables affect performance, however, may differ across memory tests. The dissociations between performance among repetition tests, and between repetition tests and other types of memory tests, is interpreted according to a task-specific, component-process approach to memory.

Adult↗
PubMed1987

Backward masking of lateralized faces by noise, pattern, and spatial frequency.

Experiments 1 and 2 measured the critical interstimulus interval at which a face presented to the right or left visual field escaped a trailing noise, pattern, or spatial-frequency mask. The function relating target duration to critical ISI was multiplicative in the noise and spatial-frequency condition, but additive at longer durations in the pattern mask condition. An advantage of about 8 msec for the left visual field and 2 msec for the right field was found in the pattern and spatial-frequency masking condition, respectively. No consistent visual field differences were found in the noise mask condition. Taken together, these results suggest that hemispheric difference in face recognition are either absent or inconsistent at early, peripheral, energy-sensitive stages of processing, but emerge strongly at higher order central stages. The results also suggest that the left and right hemispheres are not differentially sensitive to the output of high- and low-spatial-frequency channels, respectively. If it is assumed that the central face processor is functionally localized to the right hemisphere, one can infer from these results that interhemispheric transmission time is not greater than 8 msec, and the output of sensory analysis and/or relational features are transferred across the interhemispheric commissures.

Adolescent↗
PubMed1987

Contextual cuing and memory performance in brain-damaged amnesics and old people.

In Experiment 1, groups of Korsakoff amnesics and alcoholic controls learned a list of paired-associate words in a standard testing room or in a room with distinctive contextual features. Recall was tested 48 hr later in the same or other context. This procedure was repeated in Experiment 2 with old people living in institutions or in the community, but matched for age, health, education, and socioeconomic background. The amnesic patients and institutionalized old people, relative to their comparison groups, were more impaired in recalling the lists under standard conditions and were more responsive to contextual cuing, especially when the distinctive cues were provided during original learning. The results highlight the susceptibility to interference of Korsakoff amnesics and institutionalized old people and offer further evidence that both groups are more responsive to salient contextual cues than either young people or old people living in the community.

Aged↗
PubMed1986

Maturation of cytolytic T lymphocytes.

We have studied the maturation of cytotoxic T-lymphocytes (CTL) following primary and anamnestic responses in vivo and in vitro. Parameters evaluated included: frequency of effector CTL, specificity of binding to and lysis of target cells, killing and recycling ability of individual CTL, and the avidity of effector-target conjugation. While the frequency of effector CTL in the peritoneal cavity of BALB/c mice immunized against leukemia EL4 of C57BL/6 origin increases from 0 to 35% in 11 days of priming, a paradoxically lower frequency has been observed usually after 2 degrees and repeatedly after 3 degrees immunizations both in the peritoneal cavity and in the spleen. The H-2 haplotype and H-2 sub-loci specificity of CTL is preserved upon repeated immunizations. Likewise, the rate of killing and recycling of individual CTL do not change throughout immunizations, suggesting that the cytolytic activity of individual effector CTL is discrete ("quantal") and not subject to maturation upon repeated immunizations. On the other hand, inhibition of conjugate formation and of lysis by antibodies against target major histocompatibility complex (MHC) or effector Lyt-2 determinants is consistently less effective with 3 degrees CTL, suggesting an increase in avidity of effector/target interaction upon repeated immunizations. A striking increase in apparent avidity has been observed during CTL priming in mixed lymphocyte reaction, as deduced from blocking by target cell MHC antibodies. These results suggest that alloimmune CTL undergo maturation with respect to their ability to interact with the target, and that the composition of the responding population is subject to moderate selective processes driven by repeated antigenic stimuli.

Animals↗
PubMed1986

Afferent and efferent models of visual perceptual asymmetries: theoretical and empirical implications.

Visual laterality studies are reviewed in the framework of an afferent hierarchical information-processing model. According to this model, the hemispheres are viewed as separate information-processing systems, each with its own components and resources, as well as a common pool of resources. Information is shared across interhemispheric pathways. The magnitude and direction of visual field differences are determined by two factors: the processing efficiency of the components in one hemisphere relative to the other and interhemispheric transmission to components that are functionally localized to only one hemisphere. Rules are derived for weighing the relative contribution of these to visual field differences. As designed, the model can accommodate dynamic features characteristic of competing efferent (attentional) models without sacrificing its basic structure. The model's adequacy and usefulness for interpreting and guiding research on normal and brain-damaged people is discussed.

Brain Damage, Chronic↗
PubMed1986

Memory as assessed by recognition and reading time in normal and memory-impaired people with Alzheimer's disease and other neurological disorders.

Three experiments are reported that examine the dissociations in performance on two tests of retention, speeded reading and recognition in young people, home-dwelling and institutionalized elderly people, and people with severe memory disorders. In Experiment 1, subjects read sentences in normal and in geometrically transformed script at initial presentation, 1-2 hr later, and again 4-14 days later. On the latter two occasions, they were required to distinguish old sentences that they had read previously from new ones. In general, the young and elderly subjects could distinguish old from new sentences at the short delay, and all but the institutionalized elderly people could do so at the long delay. Retention as measured by reading speed typically paralleled recognition performance in that those items that were recognized best were read most quickly. The dissociation between these two tests of retention is seen only in people with memory disorders. Although these people could not distinguish old from new items even at short delays (most could not even remember having seen any sentences), their retention as assessed by reading time was similar to that of the other groups. Old sentences were read most quickly, indicating retention of item-specific information, and reading time of new sentences improved, indicating the acquisition and retention of a general skill. Experiment 2 examined what type of item-specific information was retained. Young, elderly, and memory-disordered subjects studied weakly associated word pairs and sentences. A few minutes later they were tested on both recognition and speeded reading of old, new, and recombined pairs and sentences, the last being those in which words from a studied pair or sentence were recombined with words from other such pairs or sentences. The results of both retention tests indicated that young and elderly people could distinguish old from new and recombined items. People with memory disorders, however, again failed on recognition but performed normally on speeded reading. Like the other two groups, they read old items faster than either recombined or new items. In Experiment 3, similar results were obtained even when the word pairs were constructed using randomly associated items. The results of all three experiments suggest that on implicit tests of memory, such as speeded reading, people with memory disorders can be shown to have formed and retained new associations despite failing utterly on explicit tests, such as recognition, that require conscious recollection of a previous episode.(ABSTRACT TRUNCATED AT 400 WORDS)

Aged↗
PubMed1986

Mnemonic precedence in amnesic patients: an analogue of the AB error in infants?

Amnesic patients were able to retrieve an object hidden at an initial location after a brief delay, but subsequently failed to retrieve an object at a new location, and instead searched for it at the old place. This phenomenon, which we call mnemonic precedence, resembles the AB error that has been observed in 8-10-month-old infants. The parallel performance of amnesics and infants on object search tasks is consistent with the hypothesis that memory deficit, rather than defective object concept, plays a major role in the AB error. The influence of memory processes on tests of symbolic representation is discussed.

Adult↗
PubMed1985

Antigen/mitogen induced cytolytic activity and IL-2 secretion in memory-like CTL-hybridomas.

Memory-like monoclonal CTL hybridomas, derived from fusion of the AKR thymoma BW5147 with secondary CTL generated in vivo or in MLC cultures, have been used to study the mechanism whereby antigen/mitogen induces anamnestic CTL responses. Specifically, we have asked whether induction of cytolytic activity can be promoted by an antigenic/mitogenic signal without involvement of IL-2 receptors, IL-2, or other extrinsic factors. We have found that antigen/lectin alone can trigger the cytolytic potential of the hybridomas and induce IL-2 secretion. Pure IL-2 and conditioned medium were ineffective inducers of cytotoxicity. Moreover, IL-2 receptors were not detected on the hybrid cells before and after antigenic stimulation, demonstrating that expression of IL-2 receptors and induction of specific killing activity are not genetically linked. Non-activated and activated cells conjugated with target cells equally well, suggesting that induction of cytolytic activity involves a post target cell binding step. Close linkage between cytotoxicity and IL-2 secretion has been observed: induction of killing was consistently associated with IL-2 secretion and stimulation of both activities could be blocked by Cyclosporin A. IL-2 was secreted by the CTL hybrids as early as 3 h following stimulation. We propose that the immediate supply of IL-2 by such memory CTL enhances antigenic response of other, IL-2-dependent T cells.

Animals↗