Do people with Alzheimer's disease have a disproportionate deficit in functional knowledge?: Verbal versus motoric access to semantic memory

Healthy elderly and Alzheimer's disease (AD) volunteers participated in four conditions in which they were asked to demonstrate the function and category of a series of objects either verbally or non-verbally. When responding verbally to category judgement questions, volunteers with mild-moderate AD showed levels of performance comparable with age and IQ-matched healthy elderly, but when responding verbally to questions about an item's function, they show marked deficits. This deficit was substantially reduced, however, when they were encouraged to provide the information motorically. Healthy elderly were able to use either mode of access without difficulty. The results of this study suggest that functional semantic knowledge may not be disproportionately degraded, but that when cognitive resources are compromised, retrieval may depend more critically upon mode of access. Functional information, for example, is usually acquired by actually using the object. Verbalizing such functions would require suppressing the direct (motoric) route and accessing information in a less familiar (verbal) form. In short, for people with AD, apparent deficits in semantic knowledge may reflect deficient use of unfamiliar routes of access to the information rather than degradation of semantic knowledge per se.