Cognitive slowing in Alzheimer's disease as a function of task type and response type

Abstract

Nebes and Brady (1992) reported that the degree of cognitive slowing, as reflected in the slope of the task‐complexity function relating mean reaction times (RTs) for young and older adults, was greater for patients with Alzheimer's disease (AD) than for healthy older adults. This article focuses on a subset of the Nebes and Brady (1992) data: 22 semantic task conditions and 16 nonsemantic task conditions, all of which required a yes/no response. Multiple regression analyses confirmed, for the nonsemantic tasks, the AD‐related increase in task‐complexity slope reported by Nebes and Brady. The AD patients' task‐complexity function for semantic tasks, however, was nonlinear. In addition, the increase in no RT, relative to yes RT, was disproportionately greater for the AD patients than for healthy older adults, suggesting an increase in the level of internal noise associated with comparison processes.