Dynamic allocation of attention in aging and Alzheimer disease: Uncoupling of the eye and mind

Context: Visual attention can be distributed focally, in the direction of gaze, or globally, throughout the extrapersonal space. Aging, and especially Alzheimer disease (AD), may influence global attention, resulting in shifts of gaze to attend to the global workspace. Objective: To determine if subjects who have AD and cognitively intact older subjects shift their gaze more often than young subjects while viewing a dynamic stimulus that emphasizes global attention. Design: Experimental study of eye fixation patterns in response to a simulated driving scene with stationary and moving distractors. Setting: Urban, medical school, National Institute on Aging - funded Alzheimer's Disease Center. Participants: Thirteen subjects with mild probable AD, 13 age-comparable cognitively intact older control subjects, and 11 young control subjects. Main Outcome Measure: Proportion of eye fixations within and outside of a central region of interest encompassing the "road" surface. Results: Young controls made significantly more eye fixations (mean number of eye fixations, 47.5) than either of the other 2 groups (older controls mean, 33.2; patients with AD mean, 32.2). However, 76% of their fixations remained within the central region of interest. Older controls and subjects with AD made proportionately fewer fixations within this region (48% and 49%, respectively) than young controls and moved their eyes more often to the periphery but did not differ from one another. Conclusions: Young controls maintain central eye position regardless of peripheral distraction. Older controls move their eyes to the periphery, presumably to widen the window of attention. Subjects with mild AD did not experience an additional disadvantage beyond that associated with aging.