CATEGORY AND MODALITY DEFICITS OF SEMANTIC MEMORY IN PATIENTS WITH LEFT-HEMISPHERE PATHOLOGY

Fifty patients with left unilateral cerebral lesions and 25 with right unilateral cerebral lesions were assessed on a new test, graded in difficulty across: (1) two sets of living things (animals and fruit and vegetables); and (2) two sets of inanimate artefacts (objects with and without a skilled cultural movement implicit in their use). The test consists of coloured photographs and measures naming ability, comprehension of the spoken name, and comprehension of the written name. Category knowledge in patients with right hemisphere pathology was very similar to the normal population but within the left hemisphere group unique subgroup patterns (as well as individual profiles) were found of category- and modality-specific breakdowns of semantic knowledge. Comprehension was found to be less vulnerable for man-made artefacts in spoken form, and less vulnerable for living things in written form. Single case instances of highly circumscribed category and modality effects occurred in 18% of the group. The discrepancies recorded in these patients strongly support a semantic store that is highly organised and differentiated in terms of modality and semantic category. Furthermore, specific single cases within the series favour a model of multiple modality-based semantic stores rather than a single store