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Non-verbal semantic impairment in semantic dementia
BOZEAT, S., LAMBON RALPH, M.A., PATTERSON, K., Garrard, P. & HODGES, J.R.
Neuropsychologia 2000, 38 (9), 1207-1215
Year of publication:
The clinical presentation of patients with semantic dementia is dominated by anomia and poor verbal comprehension. Few studies have investigated semantic impairment using entirely non-verbal assessments and the few exceptions have been based on results from single cases (Breedin et al., 1994; Graham et al., 1997; Lambon Ralph & Howard, in press). This study employed sound recognition and semantic association tasks to investigate the nature of the verbal and non-verbal comprehension deficit in ten patients with semantic dementia. The patients were impaired on both verbal and non-verbal assessments, and their accuracy on these tasks was directly related to their scores on a range of other tests requiring access to semantic memory. Further analyses revealed that performance was graded by concept and sound familiarity and, in addition, identified significant item consistency across the different conditions of the tasks. These results support the notion that the patientsí deficits across all modalities were due to degradation within a single, central network of conceptual knowledge. There were also reliable differences between conditions, which we propose arise directly from the nature of the mapping between input modality and semantic memory. Words and sounds have an arbitrary relationship with meaning while pictures benefit from a degree of systematicity with conceptual knowledge about the object.