DISSOCIATION BETWEEN THE DETECTION AND PERCEPTION OF MOTION IN ALZHEIMERS-DISEASE

To better understand the damage to the motion pathway that occurs in s enile dementia of the Alzheimer type (SDAT), we developed a system to assess separately the conscious perception and unconscious detection o f motion in patients with SDAT. Motion perception thresholds were sign ificantly elevated in SDAT (n = 9) compared with controls (n = 12), bu t motion detection thresholds were normal. This dissociation between t he perception and detection of motion in early SDAT parallels histolog ic evidence of a disconnection between primary and association visual cortices. This disconnection may underlie the severe visual perception deficits seen in SDAT.