Attentional control in Alzheimer's disease

Attentional control of executive function declines during the early stages of Alzheimer's disease. Controversy exists as to whether this decline resul ts from a single global deficit or whether attentional control can be fract ionated, with some aspects being more vulnerable than others. We investigat ed three proposed domains of attention, namely (i) focal attention, based o n simple and choice reaction times; (ii) the capacity to resist distraction in a visual search task; and (iii) the capacity to divide attention betwee n two simultaneous tasks. For each domain, two levels of difficulty were us ed to study Alzheimer's disease patients, who were compared with elderly an d young control subjects. The unitary attentional hypothesis predicted that the impacts of level of difficulty, age and disease would be qualitatively similar across the three attentional domains. In fact we observed differen t patterns for each domain. We obtained no differential impairment for pati ents in the focal attentional task, whereas patients were somewhat more sus ceptible than control subjects to the similarity of the distractor items in visual search. Finally, we observed marked impairment in the capacity of A lzheimer's disease patients to combine performance on two simultaneous task s, in contrast to preserved dual-task performance in the normal elderly gro up. These results suggest a need to fractionate executive processes, and re inforce earlier evidence for a specific dual-task processing deficit in Alz heimer's disease.