Abnormal temporal dynamics of visual attention in Alzheimer's disease and in dementia with Lewy bodies.

Although attentional control processes are disproportionately impaired in dementia with Lewy bodies (DLB) compared with dementia of the Alzheimer type (DAT), previous studies have not compared directly the temporal dynamics of visual attention in DLB and DAT. We examined the magnitude of the attentional blink (AB) effect in these patients, to determine the degree to which each patient group exhibited a deficit in selecting and processing visual stimuli presented in rapid succession. Eighteen DAT, 15 DLB patients, and 33 elderly controls were tested in a rapid serial visual presentation task. Participants were asked to report 1 (single-target condition) or 2 target letters (dual-target condition) embedded in a sequence of digit distracters. The temporal dynamics of visual attention was examined by varying the number of intervening distracters between the 2 targets in the dual-target condition and by estimating the attentional blink effect as the decline in the ability to report the second target correctly after successfully identifying the first. Patients with DLB performed significantly worse than patients with DAT and controls in both the single and dual-targets conditions. In contrast, DAT patients showed a selective impairment in the dual-target condition as compared with controls. As predicted, we found that both patients with DAT and DLB showed a more pronounced and protracted attentional blink than controls, indicating a reduced ability to re-engage attention on the second target. Furthermore, when DAT and DLB patients were able to report the second target, they frequently failed to identify the first, an effect that was absent in elderly controls and particularly large and long-lasting in DLB patients. This study suggests that both DLB and DAT patients show abnormal temporal dynamics of visual selective attention, presumably due to a greater intertarget competition for limited processing capacity. More generally, these findings reinforce the notion that deficits of attentional control processes are more severe in DLB patients as compared with DAT patients.