Perception of movement and shape in Alzheimer's disease

Alzheimer's disease is the most prevalent cause of abnormal cognitive decli ne in older adults and commonly affects visual function. Recent evidence su ggests that Alzheimer's disease impairs the processing of visual motion, bu t these conclusions are based on conflicting results in the few cases studi ed, and the processing of complex motion images has not been investigated. In the present study of motion processing in Alzheimer's disease we assesse d visual functions in 63 adults: 41 with mild to moderate Alzheimer's disea se (mean age 72.3 years) and 22 without dementia (mean age 71.7 years). Pro cessing of motion cues was tested with computer animation sequences known a s random-dot cinematograms, which resemble the stimuli used to define motio n processing deficits in primates with lesions of cortical area MT. Results showed that participants with Alzheimer's disease required significantly g reater thresholds for perceiving shapes defined by motion cues compared wit h participants without dementia (P = 0.0005). There were no significant dif ferences between the two groups (P < 0.05) in static visual acuity, static spatial contrast sensitivity and, surprisingly, dynamic visual acuity, whic h was normal, and motion direction discrimination, which was relatively spa red. We conclude that mild to moderate Alzheimer's disease has significant effects on the perception of structure from motion with relative sparing of motion direction discrimination. We cannot exclude a contribution by retin al pathology, but retinal dysfunction alone cannot explain the pattern of d efects we observed, The complex motion image processing deficit we identifi ed is likely to have a cerebral basis and has the potential to affect navig ation and the recognition of objects in relative motion, as encountered dur ing walking and automobile driving.