Learning to perceive structure from motion and neural plasticity in patients with Alzheimer's disease

Recent research has demonstrated that Alzheimer's disease (AD) affects the visual sensory pathways, producing a variety of visual deficits, including the capacity to perceive structure-from-motion (SFM). Because the sensory areas of the adult brain are known to retain a large degree of plasticity, the present study was conducted to explore whether the degradation of a visual function impaired by AD can be reversed or slowed through perceptual learning. Whereas many studies directed at learning in AD examined learning capacities involving the implicit memory system, a largely preserved system in AD, the present study focused on perceptual learning involving visual deficits impaired by AD. Patients with mild or moderately severe AD (N=8 in each group) were presented with computer displays depicting SFM. Participants completed three sessions a day on three consecutive days with each session comprised of 48 trials. Displays showed eight different geometric solids rendered in three densities of a random dot texture. Participants identified the displayed object by pointing to a corresponding wooden object. Results showed impaired capacity for motion perception and SFM perception in both AD groups. However, performance of patients with mild AD improved over the nine sessions, whereas that of patients with moderate AD remained unchanged. These results suggest that the cortical circuits for SFM are still plastic in the mild AD stage.