Researchers have known that aging changes the way people see the world. However, most scientists have believed that elderly people perform more slowly and worse than young people. Some effects of aging are linked to the deterioration of vision.
"But these changes alone cannot account for age-related differences in performance," writes senior researcher Patrick J. Bennett, PhD, a psychology researcher at McMaster University in Hamilton, Ontario, Canada. His study appears in the current issue of the journal Neuron.
In their study, Bennett and his colleagues tested that theory, finding "an unusual twist on the standard 'aging makes you worse' story," says co-researcher Allison Sekuter, PhD, in a news release. The findings "provide clear insight into what is changing in the aging brain."
"It's critical to understand how aging affects vision and the brain," she adds. "We'll be in a better position to help seniors see better for longer."
Elderly Eyes Vs. Young
The study involved eight younger volunteers (averaging 23 years old) and eight elderly people (averaging 68 years old). In a series of computer-generated images, the appearance of a set of bars changed while volunteers watched. The bars first appeared small, then larger, low-contrast (light gray vs. dark gray), and high-contrast (black vs. white).
Each volunteer was asked to determine the direction in which the bars moved. Researchers monitored the time it took for them to decide.
Younger volunteers took less time when the bars were small, or when the bars were low in contrast (light gray vs. dark gray).
Elderly volunteers did better when the bars were large, and high in contrast (black vs. white).
"The results are exciting not only because they show an odd case in which older people have better vision than younger people, but also because it may tell us something about how aging affects the way signals are processed in the brain," says Bennett, in a news release.
His study indicates that, as we age, the ability of one brain cell to inhibit another is reduced, Bennett writes. That sort of inhibition helps young people find an object hidden among clutter. But it can make it hard to tune into the clutter itself.
Normally, low-contrast objects require briefer periods of presentation to discriminate the direction of motion as an object size increases. Meanwhile, high contrasting objects normally require longer presentations to discriminate motion.
When the young brain sees big, high-contrast objects (the bars), it effectively tunes out the rest of the picture. It does so through nerve pathways that help inhibit other signals. But older brains do not inhibit information in the same way. Therefore, the older brain requires less time to discriminate motion patterns — and actually performs the task better.
"As we get older, it becomes harder to concentrate on one thing and ignore everything else," says Bennett. "It takes more effort to tune out distractions. We've seen it in [brain function] and speech studies, and now we see it in vision."
Although it's not clear if those factors are all linked, performance changes in elderly people may be due to brain cells' ability to affect other brain cells. Some brain cells enhance brain signals while others inhibit them.
Sources: News release, McMaster University. Betts, L. Neuron, Feb. 2, 2005: vol 45.
By Jeanie Lerche Davis
Reviewed by Brunilda Nazario, MD
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