Investigating visual knowledge in dementia of the Alzheimer type (DAT): evidence for a structured organization

Given that certain types of semantic dysfunction in DAT have been attributed to difficulties in accessing visual knowledge, the issues of integrity of access to, and format of storage, within the "visual store" are particularly important. In these experiments, we tested 10 DAT patients and matched controls on the reality decision and part-whole matching tasks. Visual knowledge was found to be significantly impaired in the DAT group. Moreover, DAT patients displayed disproportionate deficits in accessing visual knowledge of items from nonliving categories. Results are interpreted within a framework of differential hierarchical access to visual representations of perceptually similar and perceptually distinct categories of items.