Sparing of semantic memory in Alzheimer's disease.

A number of investigators have suggested that unlike the normal elderly population, patients with Alzheimer's disease have a severe semantic-memory deficit. However, the semantic-memory tasks used in previous studies have been confounded by the heavy demands they placed on effortful processing. In the present study, 20 demented (mean age 71 yrs) and 20 normal (mean age 69.8 yrs) elderly Ss were given a battery of episodic-memory tasks and 3 tasks that examined how intact and accessible their semantic memory was under conditions that did not require effortful processing. Although the demented Ss were greatly inferior to the normal Ss on the episodic-memory tests, they performed equally well on the semantic-memory test: The naming latency of both groups was equally facilitated by a semantic prime, the recall accuracy of both normal and demented elderly for a string of letters was similarly affected by the degree to which the string approximated English orthography, and recall accuracy for a string of words was affected equally in the 2 groups by the degree to which the word string obeyed syntactic and semantic rules. (42 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The deterioration of semantic memory in Alzheimer's disease.

Semantic memory impairment is a common feature of dementia of the Alzheimer type (DAT). Recent research has shown that patients with DAT are more impaired (relative to non-demented controls) in generating exemplars from a particular semantic category (e.g., animals) than words beginning with a particular letter, exhibit an altered temporal dynamic during the production of category exemplars, are impaired on confrontation naming tasks and make predominantly superordinate or semantically related errors, consistently misidentify the same objects across a variety of semantic tasks, and have alterations in multidimensional scaling models of their semantic network that are indicative of a loss of concepts and associations. These results are consistent with the view that Alzheimer's disease results in a breakdown in the organization and structure of semantic knowledge as neurodegeneration spreads to the association cortices that presumably store semantic representations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The disparate effects of Alzheimer's disease and Huntington's disease on semantic memory.

Alzheimer's disease (AD) and Huntington's disease (HD) impair performance on semantic memory tasks, but researchers disagree on whether AD and HD cause these impairments in the same manner. According to one view, AD disrupts the storage of semantic memories, whereas HD disrupts the retrieval of semantic memories. Dissenters argue that AD, like HD, disrupts retrieval. In this study, participants generated category exemplars (e.g., kinds of fruits) for 1 min, and response latencies were examined. Relative to healthy controls, the 12 AD patients produced a larger proportion of responses earlier in the recall period, consistent with the view that AD patients quickly exhaust their limited supply of items in storage. By contrast, the 12 HD patients produced a larger proportion of their responses late in the recall period, consistent with the view that HD slows retrieval. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Retrieval blocks in episodic and semantic memory.

A retrieval block (RB) refers to impaired accessibility in retrieving target information when semantically related information is presented or retrieved prior to target retrieval. A research review reveals that RBs occur in a variety of situations, including both episodic and semantic memory tasks. RBs have been most thoroughly studied in the part-list cuing paradigm in episodic recall, but similar principles seem to operate in other situations, including the A–B, A–D interference paradigm, episodic recognition, and the tip-of-the-tongue situation. Evidence for such RBs is problematic for theories postulating automatic spreading activation among associated nodes in memory. Difficulties with theories that account for such RBs are discussed. Further research on RBs may help illuminate similar phenomena, such as the effects of Einstellung in thinking and problem solving. (French abstract) (76 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Anomia as a marker of distinct semantic memory impairments in Alzheimer's disease and semantic dementia.

Objective: Many neurologically constrained models of semantic memory have been informed by two primary temporal lobe pathologies: Alzheimer's disease (AD) and Semantic Dementia (SD). However, controversy persists regarding the nature of the semantic impairment associated with these patient populations. Some argue that AD presents as a disconnection syndrome in which linguistic impairment reflects difficulties in lexical or perceptual means of semantic access. In contrast, there is a wider consensus that SD reflects loss of core knowledge that underlies word and object meaning. Object naming provides a window into the integrity of semantic knowledge in these two populations. Method: We examined naming accuracy, errors and the correlation of naming ability with neuropsychological measures (semantic ability, executive functioning, and working memory) in a large sample of patients with AD (n = 36) and SD (n = 21). Results: Naming ability and naming errors differed between groups, as did neuropsychological predictors of naming ability. Despite a similar extent of baseline cognitive impairment, SD patients were more anomic than AD patients. Conclusions: These results add to a growing body of literature supporting a dual impairment to semantic content and active semantic processing in AD, and confirm the fundamental deficit in semantic content in SD. We interpret these findings as supporting of a model of semantic memory premised upon dynamic interactivity between the process and content of conceptual knowledge. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Retrieval rules and semantic coding in short-term memory.

Examines studies of semantic coding in short-term memory for evidence of semantic effects in the primary memory component. It is argued that all cases in which semantic factors have been shown to affect primary memory are attributable to S's utilization of retrieval rules (i.e., techniques and strategies that are stored in secondary memory but facilitate the retrieval of phonemically-coded information from primary memory). It is concluded that semantic coding produces durable secondary memory traces. (41 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Discriminating age-associated memory impairment from Alzheimer's disease.

The authors attempt to provide a better understanding of the differences between the normal memory decline characteristic of age-associated memory impairment (AAMI) and the pathological decline typical of mild Alzheimer's disease (AD). Batteries of traditional memory tests and computer-simulated everyday-memory tests discriminated between the 2 groups, which were matched on age, gender, and education, with reasonable degrees of accuracy (87.5% and 88.4%, respectively). False positives were the most frequent classification errors when using either battery. These results indicate that it is possible to use ecologically valid memory assessment paradigms without sacrificing discriminant validity. The clinical significance of discriminating mild AD from AAMI is discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The influence of semantic and perceptual encoding on recognition memory in Alzheimer's disease

Previous results from a population of patients with Alzheimer's disease (Dalla Barba and Goldblum, 1996) demonstrated that the ability of patients to make a semantic association between two items was significantly and positively correlated to their performance on a yes/no recognition task for the same items and that patients who were impaired on the semantic task did significantly worse on the recognition task than patients who were unimpaired on the semantic task. These findings gave support to a hierarchical model of organization of human memory in which episodic memory depends on the integrity of semantic memory. The present study further investigates the relationship between semantic memory deficits and episodic recognition memory in 15 patients with Alzheimer's disease and 15 controls, as a function of their semantic and perceptual encoding abilities and of their cognitive impairment in other domains. The results confirmed the previous findings and showed that, although patients heavily relied on perceptual analysis, this type of encoding did not enhance their recognition memory. Correlations analyses showed that some patients who were not impaired in the semantic association, but with particularly low scores on a verbal fluency task presented with a pattern, in recognition memory tasks, that suggests a possible early involvement of frontal lobes in this subgroup of patients.     

Retrieval monitoring and anosognosia in Alzheimer's disease.

This study explored the relationship between episodic memory and anosognosia (a lack of deficit awareness) among patients with mild Alzheimer's disease (AD). Participants studied words and pictures for subsequent memory tests. Healthy older adults made fewer false recognition errors when trying to remember pictures compared with words, suggesting that the perceptual distinctiveness of picture memories enhanced retrieval monitoring (the distinctiveness heuristic). In contrast, although participants with AD could discriminate between studied and nonstudied items, they had difficulty recollecting the specific presentation formats (words or pictures), and they had limited use of the distinctiveness heuristic. Critically, the demands of the memory test modulated the relationship between memory accuracy and anosognosia. Greater anosognosia was associated with impaired memory accuracy when participants with AD tried to remember words but not when they tried to remember pictures. These data further delineate the retrieval monitoring difficulties among individuals with AD and suggest that anosognosia measures are most likely to correlate with memory tests that require the effortful retrieval of nondistinctive information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lexical semantic and associative priming in Alzheimer's disease.

Semantic memory impairment was investigated in patients with probable Alzheimer's disease (AD) using a threshold oral word reading task to assess priming of different lexical relationships. Healthy elderly controls showed significant priming for associatively related nouns (tempest-teapot) and also for nouns semantically related either because both designate basic-level exemplars of a common superordinate category (cousin-nephew) or because the target names the superordinate category of the prime (daughter-relative). AD patients, in contrast, showed preserved priming of lexical associates but impaired priming of certain semantic relationships. They showed no priming between words designating coordinate exemplars within a category, despite preserved priming of the superordinate category label. Findings are consistent with the view that at least part of the semantic deficit in AD is due to disruption of semantic knowledge that affects relationships among basic-level concepts, more than the relationships between these concepts and their corresponding superordinate category of membership. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Implicit memory for music in Alzheimer's disease.

Short, unfamiliar melodies were presented to young and older adults and to Alzheimer's disease (AD) patients in an implicit and an explicit memory task. The explicit task was yes–no recognition, and the implicit task was pleasantness ratings, in which memory was shown by higher ratings for old versus new melodies (the mere exposure effect). Young adults showed retention of the melodies in both tasks. Older adults showed little explicit memory but did show the mere exposure effect. The AD patients showed neither. The authors considered and rejected several artifactual reasons for this null effect in the context of the many studies that have shown implicit memory among AD patients. As the previous studies have almost always used the visual modality for presentation, they speculate that auditory presentation, especially of nonverbal material, may be compromised in AD because of neural degeneration in auditory areas in the temporal lobes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Episodic and semantic memory in Alzheimer's disease and progressive supranuclear palsy: a comparative study

We compared 13 patients with dementia of the Alzheimer's type (DAT) and 9 progressive supranuclear palsy (PSP) patients, matched by age, sex, education, and the overall level of cognitive deterioration, measured by using the Dementia Rating Scale, and 12 normal controls. The results of this study confirm that the pattern of cognitive deterioration of PSP patients differs from that of DAT patients. While episodic memory is severely affected early in the course of DAT, it appears to be relatively spared in PSP. In contrast to previous suggestions, we found no evidence for differentially rapid forgetting in DAT, although we did confirm relatively preserved recognition memory in PSP. We had predicted that the performance of the DAT group on tests of semantic memory (the Boston Naming Test, the ADA Synonym Judgement Test, and the Pyramids and Palm Trees Test) would be worse than that of the PSP group. However, there was, in fact, no difference on any of these measures, except that the PSP patients showed a significantly greater deficit on the Synonym Judgement Test. We suggest that the underlying cause of the semantic memory impairment might, however, be different in the two pathologies.     

Methodological control of semantic priming in Alzheimer's disease.

We conducted a lexical-decision, semantic priming experiment that included 250- and 1000-ms stimulus onset asynchronies (SOAs) with 32 probable Alzheimer's disease (AD) and 40 older normal persons. Attention-based, controlled processes are assumed to occur only at the longer of the 2 SOAs. The AD group showed greater than normal priming in the long-SOA but not the short-SOA condition. We conclude that greater than normal AD priming is a function of controlled processing rather than semantic network degradation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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 Ss 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 S 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 Ss. These results suggest that AD patients retain their knowledge of the relative importance that the different attributes of a concept have for concept meaning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Gist memory in Alzheimer's disease: Evidence from categorized pictures.

The authors investigated gist memory (the general meaning, idea, or gist conveyed by a collection of items) for categorized color photographs in patients with Alzheimer's disease (AD) using an experimental paradigm in which participants are instructed to respond "yes" when a test item fits with a previously studied category, regardless of whether the specific item was actually studied. Compared with controls, the patients endorsed fewer studied items and similar numbers of nonstudied lure items. After the authors corrected for the baseline false-alarm rate, the patients showed a lower level of endorsements for nonstudied lure items compared with that of controls, suggesting that their gist memory is impaired. Implications of these findings for understanding gist memory and response bias in patients with AD are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Heterogeneity of semantic and visuospatial deficits in early Alzheimer's disease.

Staging of visuospatial and semantic deficits in patients with dementia of the Alzheimer type (DAT) was examined. The authors hypothesized that semantic ability would be more impaired in these patients, reflecting predominant temporal pathology early in the disease. However, in the 1st study (n?=?26). 3 patients (11.5%) had marked visual but no semantic impairment. This finding was extended in a 2nd study with a 2nd patient sample (n?=?21) and more specific tasks. Two patients (9.5%) again had visual but no semantic impairment. These studies confirm that, in patients with DAT presenting with relatively focal deficits, visual deficits sometimes occur before semantic problems. The findings are discussed with regard to the cognitive demands and neuroanatomical underpinning of the tests used and point to the necessity of using cognitively specific tests to enable accurate analysis of deficits in the context of the neuroanatomical basis of impairment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Use of semantic context by patients with Alzheimer's disease.

Used semantic-priming procedures to examine limitations in the use of semantic context by 18 patients (mean age 68.9 yrs) with Alzheimer's disease (AD) and to determine whether any such contextual effects were mediated solely through automatic processes or whether attentional processes were also involved. Three tasks were applied to examine the effect of semantic context on the performance of 18 normal elderly Ss (mean age 67.2 yrs), 18 normal young Ss (mean age 24.1 yrs), and the AD Ss. When normal and AD Ss were asked to decide whether a given item was a member of a certain category, their response times were equally affected by the item's dominance in the category. The time that AD Ss took to recognize a word was actually affected more by the semantic context provided by a priming sentence than was that of normal Ss. When asked to generate the final word of an incomplete sentence, AD Ss performed very poorly unless potential responses were highly constrained by sentence context. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Working memory in mild Alzheimer's disease and early Parkinson's disease.

Alzheimer's disease (AD) and Parkinson's disease (PD) impair working memory (WM). It is unclear, however, whether the deficits seen early in the course of these diseases are similar. To address this issue, the authors compared the performance of 22 patients with mild AD, 20 patients with early PD and without dementia, and 112 control participants on tests of inhibition, short-term memory, and 2 commonly administered tests of WM. The results suggest that although mild AD and early PD both impair WM, the deficits may be related to the interruption of different processes that contribute to WM performance. Early PD disrupted inhibitory processes, whereas mild AD did not. The WM deficits seen in patients with AD may be secondary to deficits in other cognitive capacities, including semantic memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)