Category deficits and paradoxical dissociations in Alzheimer's disease and Herpes Simplex Hencephalitis

Abstract

Most studies examining category specificity are single-case studies of patients with living or non living deficits. Nevertheless, no explicit or agreed criteria exist for establishing category-specific deficits in single-cases regarding the type of analyses, whether to compare with healthy controls, the number of tasks, or the type of tasks. We examined to groups of patients with neurological pathology frequently accompained with impaired semantic memory (19 patients with Alzheimer disease and 15 with Herpes Simplex Encephalitis). Category knowledge was examined using three tasks (picture naming, naming-to-description and features verification). Both patients groups were compared with aged- and education- matched healthy controls. The profile of each patients was examined for consistency across tasks and across different analyses; however both prove to be inconsistent. One striking findings was the presence of a paradoxical dissociation ( i.e., patients who were impaired on living things on one task and non living things on another task). The findings have significant implication for how we determine category effects and, more generall for the methods use to document double dissociation across individual cases in this literature.