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What and How: Evidence for the dissociation of object knowledge and mechanical problem solving skills in the human brain.
Authors:
HODGES, J.R., Spatt, J., PATTERSON, K.
Reference:
Proceedings of the National Academy of Science, 1999, 96, pp. 9444-9448.
Year of publication:
1999
CBU number:
3890
Abstract:
Patients with profound semantic deterioration resulting from temporal-lobe atrophy have been reported to use many real objects appropriately. Does this preserved ability reflect (i) a separate component of the conceptual knowledge system ("action semantics"), or (ii) the operation of a system that is independent of conceptual knowledge of specific objects, but rather is responsible for general mechanical problem-solving skills and triggered by object affordances? We contrast the performance of three patients - two with semantic dementia and focal temporal lobe atrophy, the third with corticobasal degeneration and biparietal atrophy - on tests of real object identification and usage, picture-based tests of functional semantic knowledge, and a task requiring selection and use of novel tools. The patient with corticobasal degeneration showed poor novel tool selection and impaired use of real objects, despite near normal semantic knowledge of the same objects' functions. The patients with semantic dementia had the expected deficit in object identification and functional semantics, but achieved flawless and effortless performance on the novel tool task. Their attempts to use this same mechanical problem solving ability to deduce (sometimes successfully but often incorrectly) the use of the real objects provide no support for the hypothesis of a separate action semantic system. While the temporal lobe system is clearly necessary to identify 'what' an object is, we suggest that sensory inputs to a parietal 'how' system can trigger the use of objects without reference to object-specific conceptual knowledge.