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Iowa City IA 52242
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UI study shows Alzheimer's disease impairs complex motion image processing
IOWA CITY, Iowa -- Individuals with Alzheimer's disease are likely to
have a harder time identifying objects while they are walking or traveling
in a vehicle than those without the disease, according to a UI study.
Dr. Matthew Rizzo, UI professor of neurology and the study's principal
investigator, found that Alzheimer's disease impairs individuals' ability
to perceive shapes defined by movement cues, such as those encountered
when people are in motion.
"These are the kinds of deficits that have the potential to increase
the risks of crashes, stumbles and falls," Rizzo said.
Alzheimer's disease is the most prevalent cause of abnormal cognitive
decline in older adults and commonly affects visual function. About 10
years ago researchers began theorizing that special cells in the retina
of the eyes of Alzheimer's patients dropped out of the retina, causing
motion-processing deficiencies. If this were the only explanation, then
all types of movement processing would be affected to a similar extent.
Rizzo wanted to find out if the problem was more complex -- occurring at
a higher level in the brain, which would mean that the disease did not
affect all types of specialized stimuli to the same degree.
"Perception of movement -- just moving in a direction -- is very
different than the perception of shapes defined by movement and perception
of moving shapes," Rizzo said. "Those seem like small distinctions,
but they are really fairly big distinctions in terms of what is being processed
and where it is being processed in the brain."
The UI investigators found that perception of shapes defined by movement
cues was especially impaired in Alzheimer's disease patients -- even for
those with mild to moderate forms of the disease. However, the study showed
that the disease did not significantly affect simpler types of motion,
such as motion direction discrimination -- seeing flow in one direction
or another -- and perceiving moving shapes, Rizzo said.
Rizzo tested 63 adults -- 41 with mild to moderate Alzheimer's disease
and 22 without dementia. In the test concerning perception of shapes defined
by movement cues, Rizzo presented the subjects with a projection of many
spatially random dots. He then attached specific motion vectors to some
dots (the signal dots) and random motions to the other (the background
"noise"). Once the movement started, the signal dots took on
the shape of either a sphere or a cube rotating in different directions.
To "see" the shapes, one's brain must have been able to combine
the different movements of the many tiny signal dots into a coherent whole
and disregard the "noise." Otherwise, a person just sees "snow"
similar to that found on a malfunctioning TV screen.
The Alzheimer's patients were abnormally sensitive to the presence of
background noise. To see the shapes, the participants with Alzheimer's
disease required more than twice as much motion signal as the control group
-- 20.4 percent as compared to 9.3 percent.
"The results, which show impairments of structure from motion,
are relevant to the understanding of the pathology of neural systems in
patients with Alzheimer's disease and the progressive impact on the daily
activities of affected people," Rizzo said.
The results of Rizzo's research are included in a recent edition of