Biomedical subjects

Sasha Bozeat

Publications and source records attributed to Sasha Bozeat.

5 recordsLinked to original sources

PubMed2006

Semantic knowledge in mild cognitive impairment and mild Alzheimer's disease.

The aim of this study was to investigate memory in patients with mild cognitive impairment (MCI) and mild Alzheimer's disease (AD). Ten patients with MCI, 11 with AD and a group of age and education matched healthy control participants were assessed on a comprehensive battery of semantic memory tests, including traditional semantic memory measures and a non-verbal test of knowledge of object use. The MCI group was impaired on tests of category fluency and all three conditions of an object knowledge test (matching to recipient, function and action), plus a difficult object-naming test. The mild AD group showed additional impairments on traditional measures of semantic memory, including naming high frequency items, comprehension and semantic association. Together these findings suggest that semantic memory impairments occur early in the course of AD, more specifically in patients with "amnesic" MCI, and provide further evidence that impaired category fluency reflects semantic breakdown.

Adult↗

PubMed2004

Structure and deterioration of semantic memory: a neuropsychological and computational investigation.

Wernicke (1900, as cited in G. H. Eggert, 1977) suggested that semantic knowledge arises from the interaction of perceptual representations of objects and words. The authors present a parallel distributed processing implementation of this theory, in which semantic representations emerge from mechanisms that acquire the mappings between visual representations of objects and their verbal descriptions. To test the theory, they trained the model to associate names, verbal descriptions, and visual representations of objects. When its inputs and outputs are constructed to capture aspects of structure apparent in attribute-norming experiments, the model provides an intuitive account of semantic task performance. The authors then used the model to understand the structure of impaired performance in patients with selective and progressive impairments of conceptual knowledge. Data from 4 well-known semantic tasks revealed consistent patterns that find a ready explanation in the model. The relationship between the model and related theories of semantic representation is discussed.

Anomia↗

PubMed2002

Apraxia, mechanical problem solving and semantic knowledge: contributions to object usage in corticobasal degeneration.

To investigate the nature of the apraxia in corticobasal degeneration (CBD) five patients with CBD and five matched controls were compared on tests of: i) meaningless and symbolic gesture production, ii) a battery of semantic tasks based on 20 everyday items (involving naming and picture-picture matching according to semantic attributes, matching gestures-to-objects, object usage from name and with the real object) and iii) a novel tool test of mechanical problem solving. All five patients showed severe impairment in the production of meaningless and symbolic gestures from command, and by imitation, and were also impaired when using real objects. Deficits were not, however, restricted to action production: four were unable to match gestures to objects and all five showed impairment in the selection and usage of novel tools in the mechanical problem solving task. Surprising was the finding of an additional semantic knowledge breakdown in three cases, two of whom were markedly anomic. The apraxia in CBD is, therefore, multifactorial. There is profound breakdown in the organisation and co-ordination of motor programming. In addition, patients show central deficits in action knowledge and mechanical problem solving, which has been linked to parietal lobe pathology. General semantic memory may also be affected in CBD in some cases and this may then contribute to impaired object usage. This combination of more than one deficit relevant for object use may explain why CBD patients are far more disabled by their dyspraxia in everyday life than any other patient group.

Aged↗

PubMed2002

The influence of personal familiarity and context on object use in semantic dementia.

Several laboratory experiments assessing the ability of patients with semantic dementia to use familiar objects have revealed deficits corresponding directly to the patients' remaining conceptual knowledge for the same items. The same patients, however, were reported to demonstrate normal use of some objects relevant to their everyday lives. The study reported here was designed to explore this apparent discrepancy by examining the influence of personal familiarity with object exemplars, and of the contexts in which they are typically used. Two patients with severe semantic impairment were given single objects that they were still using at home on a regular basis and asked to demonstrate the use of each. Performance on these items was compared with use of perceptually similar and perceptually different exemplars of the same objects. All three sets were tested in the patients' own homes and also in the laboratory. Both patients were significantly more successful at using their own objects than the perceptually different exemplars, while an advantage for 'own' relative to similar exemplars characterized one of the two patients. Familiar home context had no impact on performance. The results suggest that repeated experience with personally familiar objects helps to maintain appropriate responses to them in the face of severely degraded conceptual knowledge.

Activities of Daily Living↗

PubMed2002

When objects lose their meaning: what happens to their use?

The 8 patients involved in this study were impaired on tests assessing knowledge of objects and on the demonstration of their use. The patients' success in object use was significantly correlated with their knowledge about the objects, providing further evidence that conceptual knowledge plays a key role in object use. Having a recipient present improved performance in the moderately impaired patients, suggesting that a certain level of conceptual knowledge must remain for the additional information to be beneficial. Although overall accuracy in using the target objects was not related to our measures of affordance, the specific aspects of use afforded by the objects' structures were relatively impervious to semantic impairment, suggesting a role for affordance information when object-specific knowledge is disrupted. The patients' familiarity with the objects was an important predictor of performance. Finally, despite good performance on tests of mechanical problem solving, the patients showed very little evidence of employing these skills in their interactions with real objects.

Aged↗