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R D Nebes

Publications and source records attributed to R D Nebes.

At least 19 recordsLinked to original sources
PubMed1996

Sentence context influences the interpretation of word meaning by Alzheimer patients.

This study examined whether, in Alzheimer patients, verbal context selectively activates elements of a word's meaning that are relevant to the context. Subjects were shown a sentence ending in a target noun, followed by a question about an attribute of that target. The sentence primed either the attribute in the question, a different attribute, or no attribute. Both normals and AD patients answered the question faster when the target had appeared in a context priming that particular attribute. These results suggest that Alzheimer patients retain knowledge of semantic attributes and that these attributes are susceptible to contextual activation.

Adult↗
PubMed1995

Contextual constraint facilitates semantic decisions about object pictures by Alzheimer patients.

Semantic constraints produced by sentence context reduce the time normal adults take to decide whether a given stimulus constitutes a meaningful ending to that sentence. The mechanism responsible for this constraint effect is thought to involve generation of featural restrictions based on context. In the present study, participants heard a sentence whose last word was replaced by an object picture. They decided whether the object formed a sensible ending to that sentence. Contextual constraint present in the sentences greatly influenced decision time: the greater the constraint, the faster the decision. Alzheimer patients were as affected by contextual constraint as were normal adults. The normality of the constraint effect in Alzheimer patients suggests that they can generate featural restrictions and thus retain knowledge of the semantic attributes of objects.

Adult↗
PubMed1994

Post-ECT increases in MRI regional T2 relaxation times and their relationship to cognitive side effects: a pilot study.

This pilot study examined the hypothesis that magnetic resonance imaging T2 relaxation times of specific brain regions increase after electroconvulsive therapy (ECT) and that these increases are related to the cognitive side effects of ECT. Six depressed patients undergoing unilateral ECT were studied. The results demonstrate significant post-ECT T2 increases in the right and left thalamus, and suggest a correlation between regional T2 increase and anterograde memory impairment following ECT. These findings are consistent with a post-ECT increase in brain water content (perhaps secondary to a breakdown of the blood-brain barrier) and suggest that this process may be related to the memory impairment following ECT.

Adult↗
PubMed1994

Contextual facilitation of lexical processing in Alzheimer's disease: intralexical priming or sentence-level priming?

Studies of semantic priming (facilitation of lexical processing by a prior semantic context) suggest that semantic-memory structure remains intact in Alzheimer's disease (AD). Recently, however, it has been claimed that the priming produced by single-word primes reflects merely the facilitation of preexisting lexical associations (intralexical priming) and thus reveals nothing about semantic memory in AD. Other studies showing normal priming in AD have used sentences as primes. However, intralexical priming originating from individual words within the sentence might also account for this type of contextual priming. This possibility was examined by reanalyzing previous sentence-priming results using data only from those trials where there was little likelihood of intralexical priming. This did not change the previous pattern of priming facilitation, suggesting that the normal sentence priming found in AD patients derives from the message conveyed by the sentence as a whole, rather than from simple intralexical associations.

Aged↗
PubMed1993

Phasic and tonic alertness in Alzheimer's disease.

Phasic alertness (the rapid mobilization of resources to process an expected stimulus) was examined in Alzheimer patients and normals by a choice RT task in which the stimulus was usually preceded by a warning signal. The time subjects needed to attain maximal phasic alertness was determined by varying the Stimulus Onset Asynchrony (SOA) between the warning and the stimulus. In comparison to trials without any warning, presentation of a warning signal reduced the RT of Alzheimer patients as much as it did that of normals. Similarly, the SOA necessary for maximal alertness was the same in Alzheimer patients and in normals. Maintenance of tonic alertness was investigated by examining how RT changed across a long period of continuous testing. Alzheimer patients and normals showed a similar rise in RT with increasing time on task. These results suggest that phasic and tonic alertness are relatively unimpaired by Alzheimer's disease.

Adult↗
PubMed1992

Generalized cognitive slowing and severity of dementia in Alzheimer's disease: implications for the interpretation of response-time data.

A meta-analysis was performed on the response times (RTs) of Alzheimer patients and normal subjects for 61 experimental conditions. Regression of the RTs of Alzheimer patients against those of young normals yielded a linear function: Alzheimer (time) = A+B Young (time), where B was a constant proportion of 2.3. As dementia severity increased, so too did the magnitude of this RT slowing, B rising from 2.0 to 2.9. The linearity of this function suggests that Alzheimer's disease produces a generalized slowing of cognitive processing. Since Alzheimer patients are proportionally slower than normals, the size of the absolute difference in RT between Alzheimer patients and normals increases as task complexity rises, irrespective of the exact cognitive operations being tested. It will be necessary to take this generalized slowing into account when interpreting differences in the effect that various experimental conditions have on the RTs of normals and Alzheimer patients.

Aged↗
PubMed1992

Cognitive slowing in Alzheimer's disease and geriatric depression.

Response slowing on psychological tasks is found both in Alzheimer's disease and depression. However, the underlying cause for this slowing may be different in the two disorders. This research examined whether the behavioral slowing found in Alzheimer patients results from a reduction in their rate of cognitive processing, whereas the slowing in depressed geriatric patients reflects a purely motor retardation. This hypothesis was tested using a task in which subjects had simply to determine the number of dots present in an array (i.e., enumeration). In all four subject groups (Alzheimer patients, depressed geriatric patients, healthy old controls, and healthy young controls), response time increased linearly with array size. The slope of this linear function (reflecting rate of enumeration) was the same in the normal and depressed patients, but was significantly greater in the Alzheimer patients, suggesting the presence of a cognitive slowing in Alzheimer's disease, but not in depression.

Aged↗
PubMed1991

A longitudinal study of word-reading ability in Alzheimer's disease: evidence from the National Adult Reading Test.

The purpose of this longitudinal study was to examine word-reading ability of subjects with probable Alzheimer's disease (AD), using the National Adult Reading Test (NART). In addition to the NART, a battery of neuropsychological tests was administered to 18 AD and 20 elderly control subjects at yearly intervals over 3 years. Repeated measures analysis with grouping factors showed that the controls scored better than AD subjects on the NART at each test date and the AD subjects scored significantly worse over time. NART scores were significantly correlated with dementia severity in AD subjects at final testing only, suggesting that the NART is sensitive to dementia severity only at the later stages of the disease. Associations between the NART and other cognitive measures yielded few significant results. Finally, error responses to NART words were summarized by type and percentage for each group at each test session.

Aged↗
PubMed1991

The effect of contextual constraint on semantic judgments by Alzheimer patients.

Subjects (Alzheimer patients, normal young and elderly individuals) heard a sentence the last word of which was missing. A visual word then appeared and the subjects decided whether it made a sensible ending to the sentence. Sentences varied in the degree to which their semantic context constrained possible endings to the sentence. The degree of contextual constraint greatly influenced response time--the greater the constraint, the faster subjects made their decisions. While Alzheimer patients were slower than normals, their decision time was affected by contextual constraint to the same degree as that of normals. Thus, the performance of Alzheimer patients was sensitive to the amount of semantic context present in sentences, and this context facilitated their ability to make conscious semantic judgements. These findings suggest that Alzheimer patients are capable of using semantic information in a task requiring attention-dependent processes.

Adult↗
PubMed1990

Aging increases the energetic demands of episodic memory: a cardiovascular analysis.

We hypothesized that older volunteers allocate more attentional resources to memory maintenance than do younger volunteers. Allocation of a resource supporting memory maintenance was inferred from performance and cardiovascular measures. Eighteen 18- to 26-year-old men and eighteen 60- to 79-year-old men performed a serial memory task both as a single task and as a dual task that added simple reaction time stimuli. Items presented early or later in the serial list created relatively low or high memory load. The results suggested that older men allocated greater attention to memory maintenance, particularly during high-memory-load items. They showed a slowing of dual-task reaction time and increased heart rate during high- vs. low-memory-load items. Cardiac and vascular reactions further suggested that memory maintenance is supported by phasic autonomic adjustments and that with age, more of this support is required for adequate maintenance of episodic memory.

Adolescent↗
PubMed1990

Preserved organization of semantic attributes in Alzheimer's disease.

This study investigated whether Alzheimer's disease (AD) disrupts the basic organization of the semantic attributes of concepts. Young and normal older subjects and AD patients were presented with a target concept followed by a stimulus word and were to decide whether the stimulus was related to the target. On those trials where it was, the stimulus was either a high-, medium-, or low-dominance attribute of the target. The higher the normative dominance, the more important the attribute to concept meaning. In all 3 subject groups, decision time varied as a function of dominance. The higher the dominance, the faster the decision. Attribute dominance affected the performance of AD patients more than that of normal subjects. These results suggest that AD patients retain their knowledge of the relative importance that the different attributes of a concept have for concept meaning.

Adult↗
PubMed1989

The effect of semantic and syntactic structure on verbal memory in Alzheimer's disease.

This study examined the ability of 17 patients with Alzheimer's disease and 17 normal-old subjects to recall short sentences that were normal, or had a disruption in either their semantic structure, their syntactic structure, or both their semantic and syntactic structure. Results showed that sentence recall performance was affected similarly in the demented and normal-old subjects by both the syntactic and semantic structure of the sentences. The presence of either type of language structure appeared to allow both normal and demented subjects to organize strings of words into multiword chunks for more efficient memory encoding.

Aged↗
PubMed1989

Focused and divided attention in Alzheimer's disease.

Visual search tasks were used to examine two aspects of selective attention (focused and divided attention) in normal young and older persons and in Alzheimer patients. Normal and demented subjects were equally efficient in using a color cue to selectively search only the relevant items in an array. Thus, focused attention abilities appear to be relatively unimpaired by Alzheimer's disease. By contrast, in comparison to normals, the search time of demented patients rose disproportionately as the number of items over which they had to distribute their attention was increased. This suggests that Alzheimer patients are less efficient than normals in dividing their attention.

Aged↗
PubMed1989

Semantic memory in Alzheimer's disease.

Patients with Alzheimer's disease have been suggested to have a semantic memory impairment not present in the normal old. This article reviews the performance of Alzheimer patients on tests of various aspects of semantic memory, including word finding, knowledge of the semantic attributes, and associates of concepts, as well as their category membership. The effect that semantic context has on cognitive processes such as lexical and semantic priming and memory encoding is also reviewed. Finally, the ability of theoretical constructs such as implicit memory and automaticity to explain intertask variability in Alzheimer patients' semantic performance is discussed.

Aged↗
PubMed1989

Automatic and attentional mechanisms of semantic priming in Alzheimer's disease.

Previous studies using a word-naming task have suggested that in demented patients, semantic priming results only from automatic spreading activation and not from attention-dependent processes. If this is true, then on a lexical-decision task where attention-dependent processes are a major source of the semantic-priming effect, demented patients should show little or no priming. To test this prediction, three groups of 16 subjects (young and normal-old individuals and patients with Alzheimer's disease) were given a Word-Naming and a Lexical-Decision task. In both tasks, the amount of semantic priming (the difference in response time to a word preceded by a semantically unassociated vs. a semantically associated word) was determined. Demented patients showed significantly greater semantic priming than either normal group on both tasks. This result argues against the hypothesis that the semantic priming found in demented patients is due solely to automatic processes.

Adult↗
PubMed1989

Clinical significance of sleep-disordered breathing in Alzheimer's disease. Preliminary data.

In a study of 15 probable Alzheimer's patients and 12 healthy elderly control subjects, Alzheimer's patients had a significantly higher apnea index (patients versus controls, mean +/- SD: 6.3 +/- 6.6 vs 1.8 +/- 2.7, P less than .05) and greater maximal duration of apnea (patients versus controls, median: 50.0 vs 28.5 seconds, P less than .001), but no significant increase in oxyhemoglobin desaturation compared with controls. (The accepted normal threshold for abnormality is an apnea index more than 5.) Although three of seven psychometric tests (odd-even, category retrieval, face-hand test) showed diurnal effects on one or more of their subscores, with Alzheimer's patients having significantly poorer scores at the AM than at PM testing, overnight change scores in the psychometric tests were not significantly correlated with severity of sleep-disordered breathing. Further, only 18.1% of the disruptive (ie, requiring intervention) nocturnal behaviors of the Alzheimer's patients were temporally linked to sleep-disordered breathing. The current data suggest that sleep-disordered breathing in nonmedicated Alzheimer's patients is relatively mild and is not a predictor of either overnight mental status changes, of disruptive nocturnal behaviors, or of daytime behavioral fluctuations. Additional studies of more severely demented patients and possibly of sleeping pill effects would be useful in further evaluating the role of sleep apnea in Alzheimer behavioral changes.

Aged↗
PubMed1988

Neuropsychological function in Alzheimer's disease. Pattern of impairment and rates of progression.

Although patients with Alzheimer's disease (AD) generally have impairments in multiple areas of cognitive function, there are those patients who appear to have neuropsychological deficits more prominent in one domain than in other domains. We examined the neuropsychological status of 86 patients with probable AD and 92 elderly control subjects and identified the patterns of impairments in the patients with AD. Independent deficits of visuoconstructional and lexical/semantic abilities were identified in a subset of patients by a principal components analysis. Individual patients were identified who were predominantly impaired in one, but not the other, neuropsychological domain. There were no striking relationships between the demographic characteristics of the patients and their pattern of deficits at the initial evaluation. There were no significant differences in age at onset or rate of progression of dementia among patients with different patterns of cognitive dysfunction. A review of the results of this and other studies suggests that the language impairment in AD may be associated with two distinct neuropsychological abnormalities: a lexical/semantic impairment that is unrelated to onset or progression of symptoms, and a syntactic impairment that may be associated with earlier onset and more rapid progression of dementia.

Aged↗