Speed of information processing and attention in early Alzheimer's dementia

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Abstract
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.