Cognitive estimation in patients with probable Alzheimer's disease and alcoholic Korsakoff patients.

Cognitive estimation is an important function in daily living. In early studies it was proposed that estimation deficits are associated with frontal lobe damage and executive dysfunctions. In this study, we assessed Alzheimer patients and patients with alcoholic Korsakoff's syndrome with a newly developed cognitive estimation task. We compared their performance with respect to different dimensions of estimation ('size', 'weight', 'quantity', and 'time') and to various error types. Compared to healthy controls, both patient groups were strongly impaired in all tested estimation dimensions, with Alzheimer patients performing generally worse than Korsakoff patients, except for the dimension "time". Alzheimer as well as Korsakoff patients produced so-called 'bizarre errors' and errors in the choice of the correct unit of measurement. In both patient groups cognitive estimation correlated highly with general knowledge. The production of bizarre errors and unit errors correlated with general knowledge as well as with working memory and executive functions. Results support the main assumptions of a model of cognitive estimation, described in the discussion, that specific parts of the semantic memory system as well as executive functions, in form of a plausibility check of the generated answer, are involved in the process of cognitive estimation.