Priming and semantic memory loss in Alzheimer's disease

Semantic memory (SM) was investigated in six patients with probable Alzheimer's disease (AD) by on-line measurement of semantic priming in a lexical decision task, and off-line tests of comprehension. Detailed assessment was carried out on naming, name comprehension, and probes of semantic knowledge with a battery of 150 items. The patients performed normally on perceptual tests and displayed an item-specific loss of knowledge on the semantic tests. In a primed lexical decision task, greater semantic priming was found relative to age-matched normals. The priming was substantially greater for items with "degraded" representations as determined by the off-line tests. Lexical decision was also performed more slowly on these items. These unexpected results demand a reevaluation of the concepts of the lexicon and semantic memory structure and their possible alteration in dementia.     

Reduced short-term memory capacity in Alzheimer's disease: The role of phonological,lexical, and semantic processing

Individuals with Alzheimer's disease (AD) are often reported to have reduced verbal short-term memory capacity, typically attributed to their attention/executive deficits. However, these individuals also tend to show progressive impairment of semantic, lexical, and phonological processing which may underlie their low short-term memory capacity. The goals of this study were to assess the contribution of each level of representation (phonological, lexical, and semantic) to immediate serial recall performance in 18 individuals with AD, and to examine how these linguistic effects on short-term memory were modulated by their reduced capacity to manipulate information in short-term memory associated with executive dysfunction. Results showed that individuals with AD had difficulty recalling items that relied on phonological representations, which led to increased lexicality effects relative to the control group. This finding suggests that patients have a greater reliance on lexical/semantic information than controls, possibly to make up for deficits in retention and processing of phonological material. This lexical/semantic effect was not found to be significantly correlated with patients’ capacity to manipulate verbal material in short-term memory, indicating that language processing and executive deficits may independently contribute to reducing verbal short-term memory capacity in AD.     

Reduced short-term memory capacity in Alzheimer's disease: the role of phonological, lexical, and semantic processing

Individuals with Alzheimer's disease (AD) are often reported to have reduced verbal short-term memory capacity, typically attributed to their attention/executive deficits. However, these individuals also tend to show progressive impairment of semantic, lexical, and phonological processing which may underlie their low short-term memory capacity. The goals of this study were to assess the contribution of each level of representation (phonological, lexical, and semantic) to immediate serial recall performance in 18 individuals with AD, and to examine how these linguistic effects on short-term memory were modulated by their reduced capacity to manipulate information in short-term memory associated with executive dysfunction. Results showed that individuals with AD had difficulty recalling items that relied on phonological representations, which led to increased lexicality effects relative to the control group. This finding suggests that patients have a greater reliance on lexical/semantic information than controls, possibly to make up for deficits in retention and processing of phonological material. This lexical/semantic effect was not found to be significantly correlated with patients' capacity to manipulate verbal material in short-term memory, indicating that language processing and executive deficits may independently contribute to reducing verbal short-term memory capacity in AD.     

Pattern of language impairment is different in Alzheimer's disease and multi-infarct dementia.

Language impairment was assessed in 33 patients with Alzheimer's disease (AD), in 52 patients with multi-infarct dementia (MID), and in 86 elderly community residents. The investigation included the D-Test Battery based on the Luria's Neuropsychological Investigation for all subjects. An extended battery of Luria's language items was used for 30 demented patients (11 AD and 19 MID patients) and 86 controls. The changes in language functions in normal subjects could be clearly differentiated from those seen in patients with mild dementia. The patients with different degrees of dementia differed also significantly from each other in regard to language impairment. Moreover, patients with AD and MID appeared to have different patterns of language impairment although the severity of dementia and the levels of orientation, mnestic, and conceptual functions were equal. AD was associated especially with a defect in understanding of grammatical structures and MID with disorders in recognition of words, naming, and repetition. The differential diagnostic capacity of 23 selected language items proved to be 97% between AD, MID, and control subjects. The results indicate that the examination of language functions is valuable in the differential diagnosis of dementia.     

Pictorial and lexical priming: Patterns of implicit memory in Alzheimer's and Parkinson's disease patients

Lexical and pictorial priming were examined in patients with Alzheimer's disease and in demented and nondemented patients with Parkinson's disease. Control subjects were divided into young and elderly. Lexical priming used a word‐stem completion task. Pictorial priming task was based on Rey's superimposed pictures test. Elderly normal subjects demonstrated lower lexical priming scores than those of young subjects. Analysis of covariance with age and educational level as covariates showed that normal controls, demented and nondemented Parkinsonian patients, and Alzheimer patients did not differ significantly on the lexical priming task. Pictorial priming scores did not differ significantly between elderly and younger controls. In contrast there was a striking impairment of pictorial priming in Parkinsonian patients, both demented and nondemented. Performance of subjects with mild Alzheimer's disease was superior to that of nondemented Parkinsonian patients. Our results suggest that performance in lexical priming task diminishes with physiological ageing but is unaffected by mild or moderate Alzheimer's disease. Our study also observes the existence of a selective pictorial priming deficit in Parkinson's disease; however, this deficit is not specific, as it is also observed to a lesser degree in Alzheimer's disease. It may therefore be concluded that the systems serving pictorial priming are both cortical and subcortical.     

Lexical and semantic fluency discrepancy scores in aMCI and early Alzheimer's disease

Episodic memory is compromised in amnestic mild cognitive impairment (aMCI), but lesser deficits in other cognitive domains are also commonly observed and may be helpful in identifying this group. The relative difference in performance on lexical and semantic fluency tasks may be a sensitive and specific measure in aMCI and early Alzheimer's disease (AD). We compared four groups of participants, 35 early AD, 47 aMCI, 24 healthy controls, and 18 depressive out‐patient controls, on semantic and lexical fluency as well as other neuropsychological tests. Early AD and aMCI patients showed a distinct pattern of semantic impairment in the two fluency measures compared with the healthy and depressive controls. The findings implicate early failure of the semantic memory system in aMCI and AD and suggest that consideration of the discrepancy in performance on semantic and lexical fluency measures may help in the early identification of AD.     

Repetition and verbal STM in transcortical sensory aphasia: a case study

The repetition performance of a patient (S.T.) with transcortical sensory aphasia is examined in four experiments with particular emphasis on the STM capacities underlying her performance. S.T.'s repetition of word strings exceeding her span (two words) is characterized by good recall of the final items and a strong tendency to lose the initial items in the input string. This pattern contrasts with the serial position effects observed in a phonologically based STM impairment, and it is suggested that a lexical-semantic impairment, also evident in S.T.'s naming and lexical comprehension, contributes to her inability to retain the primacy portions of the input string. Lexical effects obtained in her reproduction of words and nonwords, as well as word strings (Experiments 1 and 2), indicate that under conditions of impaired semantics S.T. is relying on lexical phonological information to repeat. Priming by repeated exposure (Experiment 3) failed to improve her repetition performance, indicating that access to lexical information is brief and dependent on recent phonological input. In Experiment 4, the role of syntactic structure in S.T.'s sentence repetition was examined, and it was shown that syntactic structure affects the recall of order information, but not the number of items recalled. The repetition and verbal STM abilities of this patient, in light of her total language profile, are then evaluated in the context of a language-based view of verbal STM.     

Tracking the acquisition of orthographic skills in developing readers: masked priming effects

A masked priming procedure was used to explore developmental changes in the tuning of lexical word recognition processes. Lexical tuning was assessed by examining the degree of masked form priming and used two different types of prime-target lexical similarity: one letter different (e.g., rlay-->PLAY) and transposed letters (e.g., lpay-->PLAY). The performance of skilled adult readers was compared with that of developing readers in Grade 3. The same children were then tested again two years later, when they were in Grade 5. The skilled adult readers showed no form priming, indicating that their recognition mechanisms for these items had become finely tuned. In contrast, the Grade 3 readers showed substantial form priming effects for both measures of lexical similarity. When retested in Grade 5, the developing readers no longer showed significant one letter different priming, but transposed letter priming remained. In general, these results provide evidence for a transition from more broadly tuned to more finely tuned lexical recognition mechanisms and are interpreted in the context of models of word recognition.     

Comparison between Oral and Written Spelling in Alzheimer's Disease

Written and oral spelling were compared in 33 patients with Alzheimer's disease (AD) and 25 control subjects. AD patients had poorer spelling results which were influenced by orthographic difficulty and word frequency, but not by grammatical word class. Lexical spelling was also more deteriorated than phonological spelling. Moreover, oral spelling was more impaired than written spelling in AD patients, whereas no difference was present between oral and written spelling of controls. Analysis of spelling errors showed that, for controls, errors were predominantly phonologically accurate in both spelling tasks. Significantly, AD patients produced more phonologically accurate than inaccurate errors in written spelling, whereas these errors did not differ in oral spelling. In contrast to controls who produced more constant than variable responses in oral and written spelling, AD patients made more variable responses (words correctly spelled in one task but incorrectly in the other) and they showed many instances of variable errors (different misspellings from one spelling task to the other). Two stepwise regression procedures showed that written misspellings were specifically correlated with language impairment, whereas oral spelling errors were correlated with attentional and language disorders. These results suggest that AD increases the attentional demands of oral spelling process as compared to written spelling. This dissociation argues, either for a unique Graphemic Buffer in which oral spelling requires more attentional resources than written spelling or for the hypothesis of separate buffers for oral and written spelling.     

Spoonish spanerisms: A lexical bias effect in Spanish

Lexical bias is the tendency for phonological errors to form existing words at a rate above chance. This effect has been observed in experiments and corpus analyses in Germanic languages, but S. del Viso, J. M. Igoa, and J. E. García-Albea (1991) found no effect in a Spanish corpus study. Because lexical bias plays an important role in the debate on interactivity in language production, the authors reconsidered its absence in Spanish. A corpus analysis, which considered relatively many errors and which used a method of estimating chance rate that is relatively independent of total error number, and a speech-error elicitation experiment provided converging evidence for lexical bias in Spanish. The authors conclude that the processing mechanisms underlying this effect hold cross-linguistically.     

Consequences of lexical stress on learning an artificial lexicon

Four experiments examined effects of lexical stress on lexical access for recently learned words. Participants learned artificial lexicons (48 words) containing phonologically similar items and were tested on their knowledge in a 4-alternative forced-choice (4AFC) referent-selection task. Lexical stress differences did not reduce confusions between cohort items: KAdazu and kaDAzeI were confused with one another in a 4AFC task and in gaze fixations as often as BOsapeI and BOsapaI. However, lexical stress did affect the relative likelihood of stress-initial confusions when words were embedded in running nonsense speech. Words with medial stress, regardless of initial vowel quality, were more prone to confusions than words with initial stress. The authors concluded that non-initial stress, particularly when wor segmentation is difficult, may serve as "noise" that alters lexical learning and lexical access.     

汉语词汇产生中词汇选择和音韵编码之间的交互作用

采取图画－词汇干扰实验范式,探索汉语单音节词汇产生中词汇选择和音韵编码之间的交互作用。实验一探测目标图画语义相关项的语音激活,观察到了非目标项的语音激活。实验二探测目标图画语义相关项的字形激活,未发现非目标项的字形激活。在改进实验条件的基础上,实验三验证实验一和二,并探测目标图画字形相关项的语音激活以及语音相关项的字形激活,结果未探测到语义相关项的字形或语音激活、语音相关项的字形激活,只发现了字形相关项的语音激活。实验一至三的结果表明汉语词汇产生中存在目标字字形相关项的语音激活,但不存在从音韵编码阶段至词汇选择阶段的激活反馈。综合上述结果,从是否存在多重的字形或语音激活,以及是否存在从音韵编码至词汇选择的反馈两个方面进行了讨论。研究结果倾向于支持词汇产生中层叠式理论的观点     

Word recognition in Alzheimer's disease: Effects of semantic degeneration

Impairments of word recognition in Alzheimer's disease (AD) have been less widely investigated than impairments affecting word retrieval and production. In particular, we know little about what makes individual words easier or harder for patients with AD to recognize. We used a lexical selection task in which participants were shown sets of four items, each set consisting of one word and three non‐words. The task was simply to point to the word on each trial. Forty patients with mild‐to‐moderate AD were significantly impaired on this task relative to matched controls who made very few errors. The number of patients with AD able to recognize each word correctly was predicted by the frequency, age of acquisition, and imageability of the words, but not by their length or number of orthographic neighbours. Patient Mini‐Mental State Examination and phonological fluency scores also predicted the number of words recognized. We propose that progressive degradation of central semantic representations in AD differentially affects the ability to recognize low‐imageability, low‐frequency, late‐acquired words, with the same factors affecting word recognition as affecting word retrieval.     

A Cross-Language Study of Perception of Lexical Stress in English

This study investigates the question of whether language background affects the perception of lexical stress in English. Thirty native English speakers and 30 native Chinese learners of English participated in a stressed-syllable identification task and a discrimination task involving three types of stimuli (real words/pseudowords/hums). The results show that both language groups were able to identify and discriminate stress patterns. Lexical and segmental information affected the English and Chinese speakers in varying degrees. English and Chinese speakers showed different response patterns to trochaic vs. iambic stress across the three types of stimuli. An acoustic analysis revealed that two language groups used different acoustic cues to process lexical stress. The findings suggest that the different degrees of lexical and segmental effects can be explained by language background, which in turn supports the hypothesis that language background affects the perception of lexical stress in English.     

Orienting attention within visual fields: how efficient is interhemispheric transfer?

Five experiments are reported examining the effect of attentional orienting on lexical decisions within visual half-fields. In Experiment 1, following baseline performance, subjects were instructed to improve performance to the right or left of the fixation point. In Experiment 2, trials were run in blocks with all items to one side of the fixation point. In Experiment 3, completely valid position indicators as to the location of the next item to be shown were presented prior to the stimulus item. In Experiment 4, to examine practice effects, no instructions or cuing were given to subjects. In Experiment 5, subjects were urged to improve performance, but with no instructions as to location. As a summary of our results, it can be stated that (a) consistent visual field differences in lexical decision performance are present, even when subjects were informed, prior to viewing, of the spatial location of the next stimulus item. (b) Lexical decision information initially input to one cerebral hemisphere is primarily processed in that hemisphere. Interhemispheric transfer of this type of language information seems to be done primarily as the end product of a cognitive process.     

Influence of mild cognitive impairment on visual word recognition

The present study examined the effects of normal aging and mild cognitive impairment (MCI) on visual word recognition. Madden et al. (1999) reported evidence of general slowing of cognitive processes in Alzheimer's disease (AD) patients relative to younger adults and healthy older adults using a lexical decision task. It was of interest to determine whether similar effects would be observed in MCI patients relative to healthy younger and older adults. We extended the lexical decision task paradigm developed by Allen et al. (2004b) on younger adults to an examination of the effect(s) of MCI on visual word recognition. Results from the present study showed that healthy older adults and MCI patients performed similarly. That is, both groups took longer than younger adults to process words presented in mixed-case than in consistent-case letters. Mild cognitive impairment patients, however, responded significantly more slowly than healthy older adults across all lexical decision task conditions and showed a trend toward larger case-mixing effects than healthy older adults, which suggests that MCI may result in poorer analytic processing ability. Based on the current findings, evidence of a generalized slowing of cognitive processes using a standard lexical decision task can be expanded to include not only AD patients, but also the preclinical stages of the disease as well.     

Word list generation performance in Alzheimer's disease and vascular dementia

Word list generation (WLG) was examined among clinical samples of individuals with Alzheimer's disease (AD) (n = 73) or ischemic vascular dementia (IVD) (n = 85), equivalent in age, education, current and estimated premorbid intellectual functioning, and proportion of men and women. The AD group performed significantly better than did the IVD group on lexical WLG, and a trend was observed indicating superior performance among the IVD group on categorical WLG. Within-groups, comparisons of group means, and profile analyses of individual performance patterns all indicated that persons with AD demonstrated a lexical > categorical pattern significantly more often than did IVD participants. The absolute difference in average performance between the AD and IVD groups on lexical and categorical WLG was small; the findings, however, generally support the clinical utility of the lexical > categorical WLG pattern in the differential diagnosis of AD and IVD. The patterns of performance support the presence of relative impairment in semantic processing among the individuals with AD and global deficits in retrieval and processing speed in individuals with IVD.     

Word List Generation Performancein Alzheimer's Disease and Vascular Dementia

Word list generation (WLG) was examined among clinical samples of individuals with Alzheimer's disease (AD) (n = 73) or ischemic vascular dementia (IVD) (n = 85), equivalent in age, education, current and estimated premorbid intellectual functioning, and proportion of men and women. The AD group performed significantly better than did the IVD group on lexical WLG, and a trend was observed indicating superior performance among the IVD group on categorical WLG. Within-groups, comparisons of group means, and profile analyses of individual performance patterns all indicated that persons with AD demonstrated a lexical > categorical pattern significantly more often than did IVD participants. The absolute difference in average performance between the AD and IVD groups on lexical and categorical WLG was small; the findings, however, generally support the clinical utility of the lexical > categorical WLG pattern in the differential diagnosis of AD and IVD. The patterns of performance support the presence of relative impairment in semantic processing among the individuals with AD and global deficits in retrieval and processing speed in individuals with IVD.     

汉语聋生与健听生口语叙事和书面叙事发展特征的比较研究

以小学3-5年级的汉语聋生为被试,考察其口语叙事与书面叙事的发展特征,并与健听生比较,揭示聋生叙事发展特征的特异性。结果发现：（1）无论口语叙事还是书面叙事,聋生和健听生在宏观结构上表现相当,但聋生在微观结构上表现较差。（2）在宏观结构和平均句长上,无论健听生还是聋生,书面叙事得分均显著好于口语叙事;（3）在词汇密度上,健听生在口语叙事和书面叙事上的表现相当,但聋生的词汇密度在口语叙事下表现较差。（4）在词汇丰富性和词汇密度指标上,聋生和健听生存在年级间发展特征的差异。研究结果对聋生的叙事教学有重要启示。