Dissociations between object knowledge and everyday action.

We report the case of a patient, MC, with Alzheimer's disease, who showed poor ability to name visually presented objects and poor visual access to the concepts of objects relative to a group of control patients (also with dementia). She performed well when words instead of objects were used in the various tasks. The data suggest that she has impaired access to semantic knowledge from vision. Surprisingly, she performed well when asked to perform everyday tasks with the same objects that had proved problematic in tests of visual naming and semantics. MC's pattern of performance is consistent with there being a direct route from vision to action and with the proposal that chaining between actions allows the development of action schemas which may operate even when there is impaired access to semantic knowledge.