Impairment of central auditory function in Alzheimer's disease

Accuracy and laterality of ear preference on dichotic listening (DL) tasks were compared in patients with Alzheimer's disease (AD) and a group of normal subjects, matched for age and education, using parameters (list length, stimulus matching, and order of recall), previously shown to significantly alter DL performance in normals. Alzheimer patients tended to show qualitatively similar, but significantly worse performance compared to controls as a function of increasing dichotic list length as well as stimulus set content (semantically, v. phonemically and unmatched dichotic items). Furthermore, these patients were unable to attend selectively to either the right- or left-ear and thus could not increase right- or left-ear advantages over the free recall procedure, an order of recall task easily mastered by the normal subjects. These results suggest that Alzheimer's disease is associated with a breakdown of cortical mechanisms involved in the selective allocation of attention.