Distinct visual motion processing impairments in aging and Alzheimer's disease.

Aging and Alzheimer's disease (AD) are associated with declines in the visual perception of self-movement that undermine navigation and independent living. We studied 214 subjects' heading direction and speed discrimination using the radial patterns of visual motion in optic flow. Young (YA), middle-aged (MA), and older normal (ON) subjects, and AD patients viewed optic flow in which we manipulated the motion coherence, spatial texture, and temporal periodicity composition of the visual display. Aging and AD were associated with poorer heading and speed perception at lower temporal periodicity, with smaller effects of spatial texture. AD patients were particularly impaired by motion incoherence created by adding randomly moving dots to the optic flow. We conclude that visual motion processing is impaired by distinct mechanisms in aging and the transition to AD, implying distinct neural mechanisms of impairment.