Linguistic and nonlinguistic impairments in writing: a comparison of patients with focal and multifocal CNS disorders

The hypothesis that the language disorder in Alzheimer's disease (AD) depends on degenerative brain changes in classical left-hemisphere language zones was tested by comparing the written language performances of a group of AD patients with mild-moderate dementia and left-hemisphere stroke patients with equally severe naming and auditory comprehension deficits who were in varying stages of recovery from Wernicke's aphasia. The results indicated significant qualitative group differences in performances between tasks and in errors within tasks. The findings are consistent with hypothesized disruption of more diffusely organized neurolinguistic systems in AD. The hypothesis that the language disorder in AD represents an exaggeration of the pattern of language change in normal aging was also examined by comparing the performances of AD patients to the changes that occur with very advanced normal aging. The data indicate convergence between AD and very elderly healthy subjects in some aspects of written language production.     

Longitudinal neuropsychological report of aphasia following left-subcortical hemorrhage

The neuropsychological assessments of a patient with language disturbance following left thalamic-putaminal hemorrhage over a $\text{2}\text{1}\text{2}\text{-}\text{year}$ period are presented together with premorbid measures of performance. Findings indicate that behavioral deficits which are both linguistic and nonlinguistic in nature differ from cortical aphasic syndromes in symptomatology and recovery course. The deficit pattern is also unlike that in other reported cases of left-subcortical lesions. Persistent dysarthria with fluent speech, limitation of verbal span and repetition, agraphia and anomia, and disturbances in self-regulation of behavior were noted, in addition to recovery of an initially severe auditory comprehension deficit. A distinguishing feature of this case was the relative preservation of reading comprehension in all four assessments.     

Oral reading in dementia

Reading has been thought to consist of three main processing components: the orthographic, phonological, and semantic lexicons. In traditional psycholinguistic models, these components have been treated independently such that the selective dysfunction of one does not necessarily imply the breakdown of another. Recently, it has been proposed that a word's semantic representation is essential to oral reading such that a disturbance within the semantic lexicon will disrupt processing within the orthographic and/or phonological lexicons. From this view, semantic deterioration should lead to fragmentation of the other systems contributing to reading, resulting in a specific pattern of errors during oral reading. This would include (1) a larger than normal advantage for reading words with regular spelling-to-sound correspondence over words with exception spelling, as well as the production of "regularization errors" when reading exception words; and (2) a smaller than normal difference between reading real words and pronounceable nonwords, or pseudowords (PW's). We found that patients with Semantic Dementia generally conformed to these hypothesized patterns of reading difficulty. Despite the presence of a semantic impairment, however, patients with Alzheimer's Disease, Frontotemporal Dementia, and Progressive Non-Fluent Aphasia did not demonstrate these patterns of reading difficulty. Our findings suggest that not all semantic impairments invariably lead to the disruption of the orthographic and phonological lexicons.     

Lexical but not semantic priming in Alzheimer's disease.

The hypothesis that patients with Alzheimer's disease (AD) have a disturbance in semantic processing was tested using a new lexical-priming task, threshold oral reading. Healthy elderly controls showed significant effects of priming for word pairs that are associatively related (words that reliably co-occur in word association tests) and for word pairs that are semantically related (high-frequency exemplars that belong to the same superordinate category but are not high-frequency associates). AD patients showed effects of priming for associatively related words but not for word pairs that are related only by shared semantic features. These results are consistent with the hypothesis that semantic processing is impaired in AD and suggest that independent networks of relationships among words and among concepts in semantic memory may be differentially disrupted with various forms of brain damage.     

Patterns of discourse production among neurological patients with fluent language disorders

Dissociations between impairments in microlinguistic and macrolinguistic abilities were examined in brain-damaged patients to assess whether these abilities are psychologically and neurologically distinct. The discourse productions of three groups of patients with equally severe fluent language disorders, but varying neuropathology and varying profiles of associated nonlinguistic cognitive impairments, were analyzed. Patients with fluent aphasia secondary to a single left-hemisphere CVA showed the greatest impairment on syntactic and lexical error measures taken to reflect microlinguistic abilities, but normal performance on measures of macrolinguistic organization (i.e., thematic coherence). Patients with probable Alzheimer's Disease were impaired on thematic coherence measures, but not on measures reflecting microlinguistic syntactic and phonological processes. Closed head injury patients whose primary clinical symptom was a fluent language disorder were impaired on both microlinguistic and macrolinguistic measures, which appears to parallel their deficits both in language-specific and in nonspecific, higher-order, diffusely organized cognitive processes.     

Neural correlates of successful and unsuccessful verbal memory encoding

Recent neuroimaging studies suggest that episodic memory encoding involves a network of neocortical structures which may act interdependently with medial temporal lobe (mTL) structures to promote the formation of durable memories, and that activation in certain structures is modulated according to task performance. Functional magnetic resonance imaging (fMRI) was used to determine the neural structures recruited during a verbal episodic encoding task and to examine the relationship between activation during encoding and subsequent recognition memory performance across subjects. Our results show performance-correlated activation during encoding both in neocortical and medial temporal structures. Neocortical activations associated with later successful and unsuccessful recognition memory were found to differ not only in magnitude, but also in hemispheric laterality. These performance-related hemispheric effects, which have not been previously reported, may correspond to between-subject differences in encoding strategy.     

Age vs Alzheimer's: a computational model of changes in representation

Previous research has demonstrated that the language of older adults leads to denser representations in a high dimensional model of memory than does the language of younger adults (Conley & Burgess, in press), and thus that density in the model (HAL or the hyperspace analogue to language) may constitute a useful metric in comparing memory for younger and older adults. This paper extends the previous research by examining the role of density in semantic representations that emerged from the language generated by adults with Alzheimer' s and comparing the results with age-matched normal controls. We found that, just as older adults have denser representations in semantic space than do younger adults, adults with Alzheimer's have still denser representations than normal older adults. These results support the hypothesis that greater density, normally associated in the model with good semantic depth, may in fact reach a "saturation point" and affect retrieval in older adults and especially adults with Alzheimer's.     

The role of sensory-motor information in object recognition: evidence from category-specific visual agnosia

The role of sensory-motor representations in object recognition was investigated in experiments involving AD, a patient with mild visual agnosia who was impaired in the recognition of visually presented living as compared to non-living entities. AD named visually presented items for which sensory-motor information was available significantly more reliably than items for which such information was not available; this was true when all items were non-living. Naming of objects from their associated sound was normal. These data suggest that both information about object form computed in the ventral visual system as well as sensory-motor information specifying the manner of manipulation contribute to object recognition.     

Communicative gestures in aphasia

Gestural communications of 10 mild and moderate aphasics and five controls were examined in two conditions: Face-to-face informal dyadic conversation and restricted visual access between speaker and listener. Gestural production was significantly reduced with restriction of visual access, supporting the posited communicative function of the hand and arm gestures investigated in this study. No differences were found between aphasic and control subjects in the rate of gestural communication in the natural condition of face-to-face interaction. Moderate aphasics, however, were found to produce proportionally fewer of the complex semantic modifying and relational communicative gestures and more nonspecific, nonconsensually shared, unclear gestures. Gestural complexity was significantly negatively correlated with measures of linguistic impairment for the aphasics. The relationship between the frequency and complexity of communicative gestures and concurrent verbalizations was also examined. The findings of this study provide confirmation for the view that there is an identifiable class of gestures utilized by aphasics for communication, aphasics are impaired in their gestural communicative competence in natural conditions of communication, and the quality of aphasics' gestural communications parallels changes in their verbal communication patterns.