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.     

Semantic versus phonological false recognition in aging and Alzheimer's disease

Patients with Alzheimer's disease (AD) have been found to exhibit lower levels of false recognition of semantic associates compared with healthy older adults. Because these patients may show impaired performance of episodic and semantic memory tasks, this finding could be explained by deficits in episodic memory, semantic memory, or both. The authors adapted a paradigm for comparison of semantic versus phonological false recognition. They found that: (a) patients with AD exhibited lower levels of corrected false recognition of semantic, phonological, and hybrid (mixed semantic and phonological) lists than older adults, and (b) patients with AD showed very similar levels of false recognition for all list types. These results suggest that only episodic memory deficits are necessary to explain the lower level of false recognition of semantic associates observed in patients with AD when compared to older adults. Additionally, (c) older adults showed greater levels of semantic, phonological, and hybrid false recognition than younger adults, extending previous false recognition research of semantically related words and categorized colored photographs to phonologically related words.     

Sentence repetition and processing resources in Alzheimer's disease

Sentence processing in Alzheimer's disease (AD) has been found to be influenced by several grammatical and extragrammatical factors, including phrase structure and verb-argument relations, number of propositions/verbs, and processing resource capacity. This study examines the effects of these variables on sentence production in AD. Normal control and AD subjects were asked to repeat six types of sentences varying along the above dimensions of complexity. Subjects' processing resource capacity was measured using several verbal working memory tests. AD subjects' sentence-repetition performance was impaired compared to the normal control group. Significant effects were observed for branching direction of phrase structure, canonicity of verb-argument relations, and serial position of errors. Sentence-repetition performance significantly correlated with working memory scores. The findings are interpreted within a resource capacity theory of sentence processing.     

Semantic sensitivity for prose in patients with probable alzheimer's disease

This study examined the sensitivity of patients with probable Alzheimer's Disease (AD) to the inherent semantic structure of prose. Patients and normal controls listened to prose passages and recalled the stories under immediate and delayed conditions. Subjects were also tested with a recognition format. Unlike controls and patients with mild AD, patients with severe AD were unable to differentiate high importance ideas from ideas of lower importance on free recall and recognition. These results suggest relative impairment of semantic processing at the encoding and consolidation process of memory in more advanced AD.     

Use of semantic context by patients with Alzheimer's disease

In this study we used semantic-priming procedures to examine limitations in the use of semantic context by patients with Alzheimer's disease. We also tried 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 and 18 normal young subjects, and on 18 patients with Alzheimer's disease. When normal and demented subjects were asked to decide whether a given item was a member of a certain category, results showed that their response times were equally affected by the item's dominance in the category. The time that demented patients took to recognize a word was actually affected more by the semantic context provided by a priming sentence than was that of normal subjects. When asked to generate the final word of an incomplete sentence, demented subjects performed very poorly unless potential responses were highly constrained by sentence context.     

Verb agreements during on-line sentence processing in Alzheimer's disease and frontotemporal dementia

An on-line "word detection" paradigm was used to assess the comprehension of thematic and transitive verb agreements during sentence processing in individuals diagnosed with probable Alzheimer's Disease (AD, n=15) and Frontotemporal Dementia (FTD, n=14). AD, FTD, and control participants (n=17) were asked to listen for a word in a sentence. Unbeknownst to the participants, the target word followed an agreement involving a verb's transitivity or thematic role component. Control participants took significantly longer to respond to a target word only when it immediately followed a violation of a thematic role agreement or a transitivity agreement, relative to target word detection immediately following the corresponding correct agreement. AD patients were selectively insensitive to thematic role agreement violations, although they demonstrated a normal processing pattern for transitivity agreements. This is consistent with previous observations showing selective difficulty with the thematic role component of a verb in AD. FTD patients were insensitive to violations of thematic role and transitivity agreements. FTD patients' impairment for both transitivity and thematic role agreements may reflect a broader degradation of verb knowledge that involves both grammatical and semantic representations, or difficulty processing sentence structure that also causes a thematic role deficit.     

Focused attention deficits in patients with Alzheimer's disease and mild cognitive impairment

Reaction time (RT) tasks take various forms, and can assess psychomotor speed, (i.e., simple reaction time task), and focused attention (i.e., choice reaction time (CRT) task). If cues are provided before stimulus presentation (i.e., cued choice reaction time (CCRT) task), then a cueing effect can also be assessed. A limited number of studies have addressed the nature of focused attention impairments in Alzheimer's disease (AD). Additionally, it is unknown whether similar impairments occur in Mild Cognitive Impairment (MCI). The current study used three RT tasks to address the nature of focused attention impairments in AD and MCI subjects. The results suggest that there were significant CRT and CCRT differences in AD subjects when compared to NECs. Furthermore, slowed RTs were also present in the MCI group, which provides evidence for impaired focussed attention and the inability to benefit from a cue in both the MCI and AD groups. The implications of the impairments related to the MCI group could potentially prove useful in early diagnosis of cognitive impairments in the elderly.     

Semantic processing of mathematical gestures

Objective

To examine whether or not university mathematics students semantically process gestures depicting mathematical functions (mathematical gestures) similarly to the way they process action gestures and sentences. Semantic processing was indexed by the N400 effect.

Results

The N400 effect elicited by words primed with mathematical gestures (e.g. “converging” and “decreasing”) was the same in amplitude, latency and topography as that elicited by words primed with action gestures (e.g. drive and lift), and that for terminal words of sentences.

Significance and conclusion

Findings provide a within-subject demonstration that the topographies of the gesture N400 effect for both action and mathematical words are indistinguishable from that of the standard language N400 effect. This suggests that mathematical function words are processed by the general language semantic system and do not appear to involve areas involved in other mathematical concepts (e.g. numerosity).     

Semantic processing in an incidental learning task

Recent research on implicit learning has suggested that perceptual learning could account for the observed dissociation between task performance and associated verbal knowledge. We report three experiments that investigate whether performance in an incidental learning task is based on knowledge held primarily at a perceptual or a semantic level. The results indicate that, under the task conditions described, processing of the semantic content of the stimuli is an automatic process. The implications of this result for implicit learning are discussed.     

Semantic processing and organization in free recall

It was hypothesized that both semantic processing and organizational activity are necessary for optimal free recall performance. In a series of three experiments, subjects were presented with a list of randomly selected nouns and were asked to make up a meaningful sentence for each noun. The subjects also rated the difficulty of using each noun. The subjects were instructed to try to remember words that were labeled "remember" words. For words that were labeled "story" words, the subjects were instructed only to make each sentence, using the word, part of an ongoing story which each subject was to make up. A test of retention for all presented words, using retention intervals of both 1 min and 24 h, showed that the story words were always recalled better than were the remember words. However, the amount of sequential organization was the same for both the story and the remember words. Recognition performance was found to be the same for both types of words. In addition, the story words were rated as being more difficult than the remember words. It was concluded that extensive semantic processing without organization is not sufficient for optimal recall.     

Assessment of depression in patients with Alzheimer's disease: concordance among informants.

This study is an investigation of the concordance among different sources of information on ratings of depression in patients with Alzheimer's disease (AD). Informants were 75 outpatients with diagnosed AD (22 with major depressive disorder), their caregivers, and geriatric clinicians. Clinicians rated each patient on the Hamilton Rating Scale for Depression on the basis of (a) the patient's report, (b) the caregiver's report, and (c) the clinician's evaluation. Overall, patients perceived themselves as less depressed than did caregivers or clinicians; for nondepressed patients, caregivers reported patients less depressed than clinicians reported; for depressed patients, no significant differences were obtained between caregiver or clinician. Certain items were more discrepant among informants and significantly differentiated depressed from nondepressed AD patients. Level of patient dementia did not affect ratings. These findings support the need for comprehensive, accurate assessment of depression in AD patients.     

Preserved metamemorial ability in patients with mild Alzheimer's disease: shifting response bias

Patients with mild Alzheimer's disease (AD) display a greater tendency to endorse unstudied items as "old" on memory tests than healthy older adults. This liberal response bias may result in mistaken beliefs about the completion of common tasks. This research attempted to determine whether it was possible to shift the response bias of mild AD patients to be more conservative on a recognition memory test through behavioral intervention. Patients with mild AD and matched controls were evaluated with two almost identical paradigms, separated by about one week. For each session, 30 words were studied and 60 words (half studied, half novel) were shown at test. During one session participants were told that 30% of words were old, and at the other session that 70% were old. We found that both groups were able to shift their response bias between the two conditions. That patients with mild AD were able to successfully shift their response bias demonstrates that--despite their overall liberal response bias and poor memory relative to controls--one component of metamemorial ability is preserved in patients with mild AD.     

Semantic processing of unattended parafoveal words

The influence that a context word presented either foveally or parafoveally, may exert on the processing of a subsequent target word was studied in a semantic decision task. Fourteen subjects participated in the experiment. They were presented with word-nonword pairs (prime). One member of the pair (which the subjects had to attend to) appeared centrally, the other parafoveally. The prime was followed by a target at two inter-stimulus intervals (ISI; 200 and 2000 msec). The word stimulus of the pair could be semantically related or unrelated to the target. The subjects' task was to classify the target as animal or not animal by pressing one of two buttons as quickly as possible. When the target word was semantically associated with the foveal (attended) word the reaction times were faster for both ISIs; when it was associated with the parafoveal (unattended) word in the prime pair, there were facilitatory effects only in the short ISI condition. A second experiment was run in order to evaluate the possibility that the obtained results were due to identification of the parafoveal stimulus. The same prime-target pairs of experiment 1 (without the target stimuli) were used. The prime-target pairs were presented to fourteen subjects who were requested to name the foveal (attended) stimulus and subsequently, if possible, the parafoveal (unattended) one. Even in this condition, percentage of identification of the unattended word was only 15%, suggesting that previous findings were not due to identification of unattended stimuli. Results are discussed in relation to Posner and Snyder's (1975) dual coding theory.     

Acoustic markers associated with impairment in language processing in Alzheimer's Disease

This study broaches in a novel way the analysis of cognitive impairment characteristic of the early stages of Alzheimer's Disease (AD). Specifically, we attempt to determine the acoustic speech parameters that are sensitive to the onset of the disease, and their association with the language deficit characteristic of AD. Speech analysis was carried out on 21 elderly patients with AD using Praat software, which analyzes the acoustic components of speech. The data obtained were subjected to stepwise regression, using the overall scores obtained in the test as the criterion variable, and the scores on the frequency, amplitude and periodicity variables as predictors of performance. We found that the percentage of voiceless segments explains a significant portion of the variance in the overall scores obtained in the neuropsychological test. This component seems to be related mainly to the patient's ability in phonological fluency. This finding could permit the creation of a diagnostic test for AD through analysis of the acoustic speech parameters at very low cost in terms of both time and resources.     

Cognitive plasticity in Alzheimer's disease patients receiving cognitive stimulation programs

The main purpose of this article is to examine whether cognitive plasticity increases after cognitive training in Alzheimer's disease patients. Twenty six patients participated in this study, all of them diagnosed with mild Alzheimer's disease, 17 of them received a cognitive training program during 6 months, and the other 9 were assigned to the control group. Participants were assigned to experimental or control conditions for clinical reasons. In order to assess cognitive plasticity, all patients were assessed before and after treatment with three subtests from the "Bateria de Evaluación de Potencial de Aprendizaje en Demencias" [Assessment Battery of Learning Potential in Dementia] (BEPAD). After treatment, Alzheimer's disease patients improved their performance in all the tasks assessing cognitive plasticity: viso-spatial memory, audio-verbal memory and verbal fluency. However, the cognitive plasticity scores of the patients in the control group decreased. In conclusion, this study showed that cognitive stimulation programs can improve cognitive functioning in mildly demented patients, and patients who do not receive any cognitive interventions may reduce their cognitive functioning.