SPEED OF INFORMATION-PROCESSING AND ATTENTION IN EARLY ALZHEIMERS DEMENTIA

The speed of information processing was examined in a group of patients in the early stages of Alzheimer's disease (AD) and in a group of healthy, age-and educationally matched controls. Subjects were tested on auditory simple-reaction time (RT), visual choice-RT, and combined simple- and choice-RT tasks. The choice-RT task required elementary linguistic or visuoperceptual matching of successively presented stimuli. AD patients had normal simple RTs but had delayed RTs on the matching tasks, suggesting a slower rate of processing for the component mental operations of the matching tasks. Estimates of the attentional demands or costs of these mental operations-stimulus encoding, decision making, and response selection-were obtained by combining the matching task with the simple-RT task (probe-RT). AD patients again showed a significant slowing in choice-RT, although they exhibited normal accuracy or performance outcome. AD patients also showed increased attentional cost for letter encoding (as reflected in increased probe-RT) but not for the other constituent mental operations. The results suggest that the differential slowing of choice-RT in AD is related to the complexity and attentional demands associated with coordinating and executing the matching tasks.