Hemispatial neglect on visual search tasks in Alzheimer's disease

Abnormal visual attention may underlie certain visuospatial difficulties in patients with Alzheimer's disease (AD). These patients have hypometabolism and neuropathology in parietal cortex. Given the role of parietal function for visuospatial attention, patients with AD may have relative hemispatial neglect masked by other cognitive disturbances. Fifteen patients with mild-to-moderate AD and 15 healthy elderly controls matched for age, sex, and education were compared on four measures of neglect: the visual search of a complex picture, a letter cancellation task, the Schenkenberg line bisection test, and a computerized line bisection task. Compared with controls, the group with AD was significantly impaired overall in attending to left hemispace on both picture search (F[1,56] = 11.27, p < 0.05) and cancellation tasks (F [1,112] = 12.68, p < 0.01); however, a subgroup of patients with AD had disproportionate difficulty in attending to right hemispace. The performance of the groups did not differ on either of the line bisection tasks regardless of the hand used. In AD, hemispatial neglect on visual search tasks may relate to difficulty in disengaging attention or in visual exploration, as well as to the severity of the disease. Future investigations may implicate neglect in visually related deficits in AD, for example, the prominent difficulty with left turns on driving a car.