We report five patients with a stereotyped clinical syndrome characterized by fluent dysphasia with severe anomia, reduced vocabulary and prominent impairment of single-word comprehension, progressing to a stage of virtually complete dissolution of the semantic components of language. A marked reduction in the ability to generate exemplars from restricted semantic categories (e.g. animals, vehicles, etc.) was a consistent and early feature. Tests of semantic memory demonstrated a radically impoverished knowledge about a range of living and man-made items. In contrast, phonology and grammar of spoken language were largely preserved, as was comprehension of complex syntactic commands. Reading showed a pattern of surface dyslexia. Autobiographical and day-to-day (episodic) memory were relatively retained. Non-verbal memory, perceptual and visuospatial abilities were also strikingly preserved. In some cases, behavioural and personality changes may supervene; one patient developed features of the Kluver-Bucy Syndrome. Radiological investigations have shown marked focal temporal atrophy in all five patients, and functional imaging by single positron emission tomography and positron emission tomography (one case) have implicated the dominant temporal lobe in all five. In the older literature, such cases would have been subsumed under the rubric of Pick's disease. Others have been included in series with progressive aphasia. We propose the term semantic dementia, first coined by Snowden et al. (1989), to designate this clinical syndrome.
This paper reports an investigation into an apparent category-specific disorder in a young woman whose semantic memory was impaired following a road accident. In Experiment 1, an impairment for processing specific items in tasks of naming pictures and defining words was related to a selective impairment for living things and also to the familiarity level of the items. In Experiment 2, a difference in semantic category (living or nonliving) was pitted against a difference in familiarity (high or low) in a picture-naming task. A significant effect of familiarity was found, but no effect of semantic category. It was shown that, in a widely used set of published pictures, living things were generally of lower familiarity than nonliving things. Moreover, measures of familiarity were shown to be confounded with some reported evidence in support of a selective impairment to living things. It was concluded that, at present, there is no convincing evidence to support the theory that semantic memory is organised into dissociable categories of living and nonliving things.
I NTRO DU CTlO NIn 1981, Warrington described two patients (JBR and VER) who showed a double dissociation between their comprehension of objects on the one hand, and animals, plants, and food on the other. This dissociation was described as a distinction between the processing of living and nonliving things, and was argued to reflect the organisation of information in semantic memory. Since then, further patients have been reported who showed similar dissociations; most have shown impairments to living things relative to nonliving (
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