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)     

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)     

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 from semantic memory and its implications for Alzheimer's disease.

In 3 experiments, participants generated category exemplars (e.g., kinds of fruits) while a voice key and computer recorded each response latency relative to the onset of responding. In Experiment 1, mean response latency was faster when participants generated exemplars from smaller categories, suggesting that smaller mental search sets result in faster mean latencies. In Experiment 2, a concurrent secondary task increased mean response latency, suggesting that slowed mental processing results in slower mean latencies. In Experiment 3, the mean response latency of Alzheimer's participants was faster than that of elderly controls, which is consistent with the idea that the semantic memory impairments of Alzheimer's disease patients stem primarily from a reduction in available items (as in Experiment 1) rather than retrieval slowing (as in Experiment 2). (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.     

The effects of perceptual interference at encoding on implicit memory, explicit memory, and memory for source.

lnterfering with stimulus identification can enhance later explicit memory performance. This counterintuitive (and theoretically unexpected) phenomenon was investigated in 5 exps. Perceptual interference enhanced category-cued recall (a conceptually driven explicit test) but had no effect on a comparable implicit memory test, category-exemplar production. This dissociation was obtained across higher levels of priming and with high-frequency as well as low-frequency exemplars. Furthermore, although perceptual interference enhanced old-new recognition memory, it did not enhance rhyme recognition (a data-driven explicit test) or source discriminability. Explanations based on enhanced semantic elaboration or enhanced encoding of spatio-temporal context do not account for the perceptual-interference effect. An account based on compensatory processing of higher level perceptual representations remains viable and is discussed in terms of the transfer-appropriate processing framework and the item-specific-relational distinction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

When false recognition is unopposed by true recognition: Gist-based memory distortion in Alzheimer's disease.

The authors examined false recognition of semantic associates in patients with probable Alzheimer's disease (AD), older adults, and young adults using a paradigm that provided rates of false recognition after single and multiple exposures to word lists. Using corrected false recognition scores to control for unrelated false alarms, the authors found that (a) the level of false recognition after a single list exposure was lower in AD patients than in controls; (b) across 5 trials, false recognition increased in AD patients, decreased in young adults, and showed a fluctuating pattern in older adults; and (c) all groups showed an increase in true recognition over the 5 trials. Analyses suggested that AD patients built up semantic gist across trials, whereas both control groups were able to use increased item-specific recollection and more conservative response criteria to suppress gist-based false alarms. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Facilitation by semantic priming in Alzheimer's disease and control groups matched for accuracy of word recognition.

Facilitation of word recognition was compared for Alzheimer's disease (n?=?10) and elderly control (n?=?10) groups in an experimental paradigm developed by T. R. Kwapil, D. C. Hegley, L. J. Chapman, and J. P. Chapman (1990). The task involved presenting a priming word to a participant followed by a related, neutral, or unrelated target word in a degraded form. The participant's task was to recognize the target word. Level of degradation was manipulated during a series of practice trials so that the overall accuracy of target word recognition for the neutral and related words was about 50%. The purpose of this manipulation was to minimize the artifactual effect of overall accuracy of word recognition on difference scores. With an overall accuracy level of 57% on the experimental trials for both groups, a smaller facilitation effect was found for the Alzheimer group than for the controls. (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)     

Limitations of the distinctions between conceptual and perceptual implicit memory: A study of Alzheimer's disease.

Previous studies suggested that perceptual implicit memory is spared in Alzheimer's disease (AD) but conceptual implicit memory is not. This dissociation is often invoked to support views of implicit memory that distinguish between perceptual and conceptual processing or systems. This study investigated an alternate hypothesis: that methodological differences between perceptual and conceptual implicit tests could account for differences in performance. Fourteen AD participants, 16 elderly controls, and 16 younger controls participated in structurally parallel conceptual and perceptual tests of implicit memory that required production of studied items. Results showed normal perceptual and conceptual priming when participants with AD generated items at study but impaired priming in both tests when they merely repeated items. These results are inconsistent with both systems and processing views of implicit memory and suggest that similarity of study and test procedures is more important than the inferred theoretical construct. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

On the relation between perceptual priming and recognition memory.

Two experiments evaluated the hypothesis that perceptual fluency is used to infer prior occurrence. Subjects heard (Experiment 1) or saw (Experiment 2) a list of words and then were presented in the same modality with both these and other words twice in succession: first in a more or less impoverished fashion, and then in clear fashion. For the first of these two presentations, the subjects tried to identify the word; for the second, they gave a recognition judgment. As predicted by the perceptual fluency hypothesis, and as has been found in previous research, the recognition judgments were more positive for identified words than for unidentified words. However, degree of impoverishment, by which apparent perceptual fluency was brought under experimental control, did not affect the recognition judgments. The perceptual fluency hypothesis was therefore not supported, and the observed relation between identification and recognition was attributed to an item selection effect. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Long-term perceptual specificity effects in recognition memory: The transformed pictures paradigm.

The effects of a study/test mismatch in the viewing mode of natural scenes on recognition memory performance were examined. At both encoding and retrieval, scenes were presented either by being divided into quarters that were displayed in a sequential cumulative fashion or by scrolling the images through the screen, thereby gradually revealing the content of the images. Half of the participants were tested immediately after encoding and the other half after 48 hours. For both the immediate and delayed retrieval conditions, better recognition memory was demonstrated when viewing modes matched across study and test than when they mismatched. Implications for current processing and multiple systems views of memory are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conceptual and perceptual implicit memory in Huntington's disease.

The aims of this study were to examine and compare perceptual and conceptual implicit memory (CIM) in Huntington's disease (HD) and to characterize the relationship between tests of frontal lobe functioning and CIM. Sixteen HD patients and 16 normal controls completed structurally parallel tests of perceptual implicit memory and CIM (i.e., rhyme and category exemplar generation), tests of explicit memory, and verbal fluency. HID patients showed intact implicit memory for both rhyme and category exemplars, despite evidence of frontal dysfunction on other tests. An unexpected finding was that patients showed a deficit in cued rhyme generation that correlated with severity of neurological impairment. The authors replicated findings in controls of a correlation between letter fluency and CIM but found no relationship in patients. Frontal dysfunction in HID may lessen the influence of generative strategies on tests of CIM without compromising performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

ERP assessment of semantic memory in Alzheimer''s disease

We present the technical details of a new system for the synchronous recording and review of a combined oesophageal manometry and video fluoroscopic barium swallow examination. The system developed uses a portable manometry recorder and personal computer (PC) with an integrated digital video acquisition system. These are controlled using software to enable the real time capture of digital video and manometric data throughout the combined examination. The recorded pressure waveforms can then be synchronously displayed on a screen with the recorded digital video of the fluoroscopic barium swallow. This new tool enables both comparative measurement and detailed analysis of the relationship between visualized bolus transport and pressure measurements. It provides for a deeper understanding and improved clinical assessment of complex motility disorders over those obtained when these two modalities are applied separately. The system is easily incorporated into a clinical radiology suite and it is both user and patient friendly. It uses readily available computer hardware together with multimedia software and is a comparatively economical addition to the radiology suite with the manometry analysis available fulfilling the criteria laid down by the Clinical Associates Group of the British Society of Gastroenterology.     

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)     

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)     

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)     

Dissociations between familiarity processes in explicit recognition and implicit perceptual memory.

Dual-process theories of recognition posit that a perceptual familiarity process contributes to both explicit recognition and implicit perceptual memory. This putative single familiarity process has been indexed by inclusion–exclusion, remember–know, and repetition priming measures. The present studies examined whether these measures identify a common familiarity process. Familiarity-based explicit recognition (as indexed by the inclusion–exclusion and the independence remember–know procedures) increased with conceptual processing. In contrast, implicit word-identification priming and familiarity-based word-stem completion (as indexed by inclusion–exclusion) increased with study–test perceptual similarity. These dissociations indicate that familiarity-based explicit recognition may be more sensitive to conceptual than to perceptual processing and is functionally distinct from the perceptual familiarity process mediating implicit perceptual memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)