Dementia, ageing, and the structure of human memory

The memory performance of patients suffering from senile dementia of the Alzheimer type (SDAT) (N = 29), normal subjects of equivalent age and education (N = 58), and young normal controls (N = 42) was tested using free recall and verbal and nonverbal span. Three measures were derived from the free recall task: primacy based on the first item, secondary memory based on the middle serial positions, and primary memory based on recency and the Waugh-Norman correction factor. The SDAT patients differed from the normal elderly on all free recall and span measures except for primary memory. The elderly were clearly inferior to the young on secondary memory, and were marginally poorer on primary memory and the two span measures. Three possible explanations of this pattern of results are considered, based on the dichotomous modal model of memory, levels of processing, and working memory. It is suggested that the assumption that SDAT patients suffer from a deficit in the central executive component of working memory offers the best of these interpretations.