Span of temporal continuity as a measure of personal and present existence.
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Adult↗
Biomedical subjects
M Moscovitch
Publications and source records attributed to M Moscovitch.
A potential application to the study of microscopic energy deposition in a solid by means of heavy charged-particle induced photochromic alterations in a tissue-equivalent matrix.
A theoretical study was carried out to investigate the feasibility of using the radiation-induced colour decay of photochromic molecules embedded in a polymer matrix as a probe for studying the microscopic energy deposition of heavy charged particles (HCPs) in a tissue-equivalent solid. The theoretical treatment makes use of the radial dose distribution function as derived from gas-phase physics, together with the effects of the increase in temperature and of matrix degradation on the colour-decay kinetics of the photochromic molecules, according to empirical models derived for the solid state. Bearing in mind the non-stochastic nature of the model, the use of gas-phase physics at the level of radiation interaction, and the fact that some empirical quantities used have been established macroscopically, all factors which signify that extra caution is required in the interpretation of the results, it is shown that when the optimum information retrieval time (after track formation) is considered the technique may be able to resolve differences in the energy deposition pattern by different HCPs in the nanometre range (1-10 nm; material's mass density 1.2 g cm(-3)) from the track axis. Most importantly, though, the present study aims to erect a theoretical framework for the possible application of the technique and to highlight those aspects which are likely to be critical to its practical usage, such as particle type and energy range, and spatial scale and magnitude of the expected effect together with its dependence on time, the physical characteristics of the matrix, and the kinetic behaviour of the type of photochromic molecule studied. Furthermore, it establishes a rationale for interpreting the experimentally observed (if available) colour changes in the HCP track in terms of the microscopic distribution of energy deposition in it.
Benzopyrans↗
Source memory and divided attention: reciprocal costs to primary and secondary tasks.
Source memory, in comparison with item memory, is more sensitive to frontal lesions and may require more strategic processing. Divided attention was used to restrict attentional resources and strategic processing on memory tasks. Participants encoded and retrieved items (i.e., words) and source (i.e., voice or spatial location) while concurrently performing a finger-tapping (FT) or visual reaction-time (VRT) task. Memory accuracy costs under divided attention were greater for retrieval of source than item and were greater with VRT than FT. Similarly, costs to the secondary task were greater when concurrently retrieving source as opposed to item and were greater for VRT than FT. Effects were stronger when spatial location was used as the source task. Findings support the idea that processing source information requires more attentional resources and effort than processing item information. Furthermore, concurrent performance of VRT produced greater interference with a task that was more dependent on intact frontal functioning and better simulated the performance of patients with frontal dysfunction.
Adult↗
Levels of processing and selective attention effects on encoding in memory.
The purpose of the present study was to investigate the effects of selective attention and levels of processing (LOPs) at study on long-term repetition priming vis-a-vis their effects on explicit recognition. In a series of three experiments we found parallel effects of LOP and attention on long-term repetition priming and recognition performance when the manipulation of these factors at encoding was blocked. When a mixed study condition was used, both factors affected explicit recognition, while their effect on repetition priming was determined by the nature of the test. Shallow processing at test did not benefit from long-term repetition, regardless of whether the words had been studied deeply or shallowly. Selective attention affected long-term repetition priming in a semantic, but not in a lexical decision (LD), test. Regardless of study condition, retention lag affected long-term repetition priming only in the semantic test. These results suggest that if the experimental conditions allow scrupulous selection of attended and unattended information or narrow tuning to a shallow, pre-lexical LOP, implicit access to unattended or shallowly studied items is significantly reduced, as is explicit recognition. We suggest a conceptual framework for understanding the effects of LOP, attention, and retention interval on performance of explicit and implicit tests of memory.
Analysis of Variance↗
Networks of domain-specific and general regions involved in episodic memory for spatial location and object identity.
Positron emission tomography (PET) was used to investigate human episodic memory for spatial location and object identity. We measured regional cerebral bloodflow (rCBF) while subjects engaged in perceptual matching of the location or the identity of line drawings of objects. Perceptual matching also involved incidental encoding of the presented information. Subsequently, rCBF was measured when subjects retrieved the location or the identity of these objects from memory. Using the multivariate partial least squares image analysis, we identified three patterns of activity across the brain that allowed us to distinguish structures that are differentially involved in processing spatial location and object identity from structures that are differentially involved in encoding and retrieval but operate across both domains. Domain-specificity was evident by increased rCBF during the processing of spatial location in the right middle occipital gyrus, supramarginal gyrus, and superior temporal sulcus, and by increased rCBF during the processing of object identity in portions of bilateral lingual and fusiform gyri. There was a nearly complete overlap between domain-specific dorsal and ventral extrastriate cortex activations during perceptual matching and memory retrieval. Evidence of domain-specificity was also found in the prefrontal cortex and the left hippocampus, but the effect interacted with encoding and retrieval. Domain-general structures included bilateral superior temporal cortex regions, which were preferentially activated during encoding, and portions of bilateral middle and inferior frontal gyri, which were preferentially activated during retrieval. Together, our data suggest that encoding and retrieval in episodic memory depend on the interplay between domain-specific structures, most of which are involved in memory as well as perception, and domain-general structures, some of which operate more at encoding and others more at retrieval.
Adult↗
Clustering and switching on verbal fluency: the effects of focal frontal- and temporal-lobe lesions.
We examined the hypothesis that, on verbal fluency, clustering (i.e. generating words within subcategories) is related to temporal-lobe functioning, whereas switching (i.e. shifting between subcategories) is related to frontal-lobe functioning. Tests of phonemic and semantic fluency were administered to 53 patients with focal frontal-lobe lesions (FL), 23 patients with unilateral temporal-lobe lesions (TL) and 55 matched controls. Performance by FL patients was consistent with our hypothesis: in comparison to controls, patients with left-dorsolateral or superior-medial frontal lesions switched less frequently and produced normal cluster sizes on both phonemic and semantic fluency. Performance by TL patients was not consistent across fluency tasks and provided partial support for our hypothesis. On phonemic fluency, TL patients were unimpaired on both switching and clustering. On semantic fluency, TL patients were impaired on switching in comparison to controls and left TL patients produced smaller clusters than right TL patients. The best indices for discriminating the patient groups, therefore, were phonemic-fluency switching (impaired only with frontal lesions) and semantic-fluency clustering (impaired only with temporal-lobe lesions).
Adult↗
Memory impairments associated with hippocampal versus parahippocampal-gyrus atrophy: an MR volumetry study in Alzheimer's disease.
Delayed memory impairments and medial temporal-lobe atrophy are considered to be cardinal features of Alzheimer's disease (AD). The goal of the present magnetic resonance (MR) volumetry study was to investigate the relationship between both features. We determined MR-derived estimates of hippocampal and parahippocampal volume in a sample of 27 AD patients and in a group of 26 healthy control subjects (NCs) of comparable age and education. We examined the performance of the two groups on immediate and delayed recall trials of an auditory-verbal list-learning task (CVLT), a visual non-verbal memory task (Visual Reproduction of the WMS-R), and a screening procedure that provides an estimate of overall cognitive functioning (DRS). Volumes of the hippocampus and the parahippocampal gyrus were significantly smaller in AD patients than in NCs. AD patients were impaired in their overall level of cognitive functioning and showed memory deficits under immediate and delayed recall conditions. The association between medial temporal-lobe atrophy and cognitive impairments in AD was found to be highly specific: Hippocampal volume correlated positively with delayed but not immediate recall of the verbal auditory list learning task. In contrast, parahippocampal gyrus volume, specifically in the right hemisphere, was positively related to delayed but not immediate recall of the non-verbal visual memory task. In NCs, there was a trend towards a negative association between hippocampal volumes and delayed verbal recall. Our results suggest that hippocampal and parahippocampal gyrus atrophy in AD are related to distinct aspects of the patients' memory impairments. Our findings have implications for current discussions regarding contributions of the hippocampus and the parahippocampal gyrus to memory in the intact human brain.
Aged↗
Consolidation and the hippocampal complex revisited: in defense of the multiple-trace model.
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Adaptation, Physiological↗
Clustering and switching on verbal fluency tests in Alzheimer's and Parkinson's disease.
Two components of verbal fluency performance--clustering (i.e., generating words within subcategories) and switching (i.e., shifting between subcategories)--were examined in patients with dementia of the Alzheimer type (DAT), patients with dementia with Parkinson's disease (DPD), nondemented patients with Parkinson's disease (NPD), and demographically matched controls. The DAT and DPD groups were impaired in the number of words generated on both phonemic and semantic fluency. The DAT group produced smaller clusters on both tasks and switched less often on semantic fluency than controls. The DPD group switched less often on both tasks and produced smaller clusters on phonemic fluency than controls. The NPD group was not impaired on any fluency variable. Thus, the total number of words generated on phonemic and semantic fluency did not discriminate the dementia groups from their respective control groups, but measures of clustering and switching did. This differential pattern of performance provides evidence for the potential usefulness of measures of switching and clustering in the assessment of dementia.
Aged↗
Age-related changes in D2 receptor binding with iodine-123-iodobenzofuran SPECT.
UNLABELLED: The purpose of this study was to evaluate the effects of age on D2 receptor binding with 123I-iodobenzofuran (IBF) SPECT. METHODS: Subjects were 40 healthy volunteers (age 19-83 yr), including 6 who had test/retest studies. Scans were acquired with a triple-head SPECT camera 3 hr postinjection of IBF (300 MBq). Striatal regions (caudate and putamen) were defined by two different region-of-interest (ROI) sets consisting of large volumes [(CLVs), 2.2 and 6.6 m] and small volumes [(SVs), 0.6 and 1.3 ml]. D2 binding (Rv=V3/V2) was quantified using our previously proposed multilinear regression technique. Effects of age on D2 binding were evaluated by fitting linear, exponential and logarithmic models. RESULTS: The mean Rvs were 26% lower than LV for both putamen and caudate than the corresponding values from the SV due to the partial-volume effect. Although the identifiability of Rv using SV deteriorated slightly, the test/retest reproducibility of Rv measurements was equally excellent for LV and SV. The mean Rvs were 11% higher for putamen compared with those for caudate. D2 binding declined significantly with age (p < 10(-5)) for all three models. The nonlinear models were slightly superior to the linear model in describing the relationship between Rv and age. In these models, D2 binding declined with age, equally for caudate and putamen at 7%-13% per decade; the decline was progressively smaller with age. CONCLUSION: IBF SPECT permitted reliable measurements of D2 binding in the caudate or putamen separately using small ROI volumes that significantly improved the quantitation loss from the partial-volume effect. Our results agreed with previous PET and postmortem findings of D2 binding losses with age. However, these age effects may be nonlinear. Age-related changes in D2 binding must be taken into consideration in clinical IBF SPECT investigations.
Adult↗
Simulation of radiation effects on three-dimensional computer optical memories.
A model was developed to simulate the effects of heavy charged-particle (HCP) radiation on the information stored in three-dimensional computer optical memories. The model is based on (i) the HCP track radial dose distribution, (ii) the spatial and temporal distribution of temperature in the track, (iii) the matrix-specific radiation-induced changes that will affect the response, and (iv) the kinetics of transition of photochromic molecules from the colored to the colorless isomeric form (bit flip). It is shown that information stored in a volume of several nanometers radius around the particle's track axis may be lost. The magnitude of the effect is dependent on the particle's track structure.
Biophysical Phenomena↗
Strategic retrieval and the frontal lobes: evidence from confabulation and amnesia.
Confabulation and amnesia are considered disorders of episodic but not of semantic memory. To test the limits of this view, retrieval from episodic and semantic memory was investigated in eight confabulating and nine non-confabulating amnesic subjects, and in 17 matched control subjects, by using a personal and an historical version of the Crovitz [Unconstrained search in long-term memory, Paper presented at the meeting of the Psychonomic Society, St Louis, MO, 1973] cue-word test. In response to cue words such as letter or battle subjects had to describe in detail, respectively, a related event from their personal lives or from history before their birth. We found that a subset of amnesic subjects, those with presumed damage or dysfunction in the region of the ventromedial frontal cortex, would confabulate in response to these cues. Their confabulations involved semantic, historical memories, as much as episodic, personal ones: and that distortions of content were at least as common as those of time. Even when not confabulating, they had much more difficulty than other amnesic subjects in recovering memories related to these cues. In confabulating, as compared to non-confabulating, amnesic subjects, prompting led to an increase in confabulations but also to greater recovery of veridical memories. By comparison, non-confabulating amnesic subjects whose memory loss was as severe as that of the confabulators, had a milder deficit on the personal as well as the historical cue-word test. They benefited from prompting somewhat more than matched control subjects. These results suggest that confabulation is associated with impaired strategic retrieval processes resulting from damage in the region of the ventromedial frontal cortex. These strategic retrieval processes help initiate and guide search in episodic and in semantic memory and they help monitor and organize the output from those systems.
Adult↗
Memory consolidation, retrograde amnesia and the hippocampal complex.
Results from recent studies of retrograde amnesia following damage to the hippocampal complex of human and non-human subjects have shown that retrograde amnesia is extensive and can encompass much of a subject's lifetime; the degree of loss may depend upon the type of memory assessed. These and other findings suggest that the hippocampal formation and related structures are involved in certain forms of memory (e.g. autobiographical episodic and spatial memory) for as long as they exist and contribute to the transformation and stabilization of other forms of memory stored elsewhere in the brain.
Amnesia↗
Clustering and switching as two components of verbal fluency: evidence from younger and older healthy adults.
Although verbal fluency is a frequently used neuropsychological test, little is known about the underlying cognitive processes. The authors proposed that 2 important components of fluency performance are clustering (i.e., the production of words within semantic or phonemic subcategories) and switching (i.e., the ability to shift between clusters). In Experiment 1, correlational data from 54 older and 41 younger adults indicated that both components were highly correlated with the number of words generated on semantic fluency, whereas switching was more highly correlated than clustering with the number of words generated on phonemic fluency. On semantic fluency, younger participants generated more words and switched more frequently than older participants; on phonemic fluency, older participants produced larger clusters than younger participants. In Experiment 2, among 22 young adults, divided attention decreased the number of words generated and decreased switching on phonemic fluency only. Overall, findings suggest that clustering and switching are dissociable fluency components and that switching is related to frontal-lobe functioning.
Adolescent↗
Correlation between frontal lobe functions and explicit and implicit stem completion in healthy elderly.
The authors investigated the relationship between performance on neuropsychological tests, which were sensitive to medial-temporal and frontal lobe function, and implicit and explicit stem completion in a group of healthy elderly participants (mean age = 77.3 years). Several stem-completion conditions varying in the size of the search space and the specificity of the cues were included. Across conditions, performance on a frontal lobe sensitive test (word fluency) and on medial-temporal tests (California Verbal Learning Test; delayed recall) correlated with explicit stem completion. The correlations between frontal and medial-temporal test performance and implicit stem completion were weaker. However, a relationship was observed between frontal lobe functioning and stem completion when (a) the search space was large and the cues were constrained and (b) when the search space was limited and the cues were relatively unconstrained. Therefore, the role of the frontal lobes in implicit stem completion seems to be to detect bias resulting from prior study, and this involvement can only be revealed when the interaction between the size of the search space and the retrieval cues (a) makes bias detection necessary and (b) allows it to play a role. The stronger involvement of the frontal lobes in explicit stem completion likely reflects strategic retrieval processes, and the medial-temporal lobe involvement may be related to verification processes.
Aged↗
Perceptual priming of proper names in young and older normal adults and a patient with prosopanomia.
The purpose of this study was to determine if normal participants and a patient with prosopanomia can be perceptually primed for proper names. To this end, 2 experiments were conducted. In Experiment 1, normative data were collected on 4 proper-name priming tasks. The variables of levels of processing at encoding and age were manipulated. Robust priming results were obtained that were not influenced by either of these variables. The results of Experiment 2 indicated that prosopanomic patient N.G. demonstrated normal repetition priming, despite her marked impairment in deliberate retrieval of person and city names. These results are interpreted in terms of a dissociation between explicit and implicit memory for proper names and suggest that the deficit in prosopanomia only involves deliberate access to the name; access to presemantic representations of the visual word form remains intact.
Adult↗
Patterns of eye movements during parallel and serial visual search tasks.
Eye movements were monitored while subjects performed parallel and serial search tasks. In Experiment 1a, subjects searched for an "O" among "X"s (parallel condition) and for a "T" among "L"s (serial condition). In the parallel condition in Experiment 1b, "[symbol: see text]" was the target, and "O"s were distractors; in the serial condition these stimuli switched roles. Displays contained 1, 12, or 24 stimuli, with both target-present and target-absent trials. RT and eye-movement measures (number of fixations, saccadic error, and latency to move) indicated that search efficiency was greatest in the parallel conditions, followed by the serial condition of experiment 1a and, finally, by the serial condition of Experiment 1b. This suggests that eye movements are correlated with the attentional processes underlying visual search.
Attention↗
Long-term semantic priming: a computational account and empirical evidence.
Semantic priming is traditionally viewed as an effect that rapidly decays. A new view of long-term word priming in attractor neural networks is proposed. The model predicts long-term semantic priming under certain conditions. That is, the task must engage semantic-level processing to a sufficient degree. The predictions were confirmed in computer simulations and in 3 experiments. Experiment 1 showed that when target words are each preceded by multiple semantically related primes, there is long-lag priming on a semantic-decision task but not on a lexical-decision task. Experiment 2 replicated the long-term semantic priming effect for semantic decisions with only one prime per target. Experiment 3 demonstrated semantic priming with much longer word lists at lags of 0, 4, and 8 items. These are the first experiments to demonstrate a semantic priming effect spanning many intervening items and lasting much longer than a few seconds.
Adult↗