As adults age, vision deteriorates. One common type of decline is in contrast sensitivity, the ability to distinguish gradations of light to dark, making it possible to discern where one object ends and another begins.
When an older adult descends a flight of stairs, for example, she may not tell the edge of one step from the next, so she stumbles. At night, an older driver may squint to see the edge of white road stripes on blacktop. Caught in the glare of headlights, he swerves.
But new research suggests that contrast sensitivity can be improved with brain-training exercises. In a study published last month in Psychological Science, researchers at the University of California, Riverside, and Brown University showed that after just five sessions of behavioral exercises, the vision of 16 people in their 60s and 70s significantly improved.
After the training, the adults could make out edges far better. And when given a standard eye chart, a task that differed from the one they were trained on, they could correctly identify more letters.
“There’s an idea out there that everything falls apart as we get older, but even older brains are growing new cells,” said Allison B. Sekuler, a professor of psychology, neuroscience and behavior at McMaster University in Ontario, who was not involved in the new study. “You can teach an older brain new tricks.”
The training improved contrast sensitivity in 16 young adults in the study as well, although the older subjects showed greater gains. That is partly because the younger ones, college students, already had reasonably healthy vision and there was not as much room for improvement.
Before the training, the vision of each adult, young and older, was assessed. The exercises were fine-tuned at the beginning for each individual so researchers could measure improvements, said Dr.G. John Andersen, the project’s senior adviser and a psychology professor at the University of California, Riverside.
During each session, the subjects watched 750 striped images that were rapidly presented on a computer screen with subtle changes in the visual “noise” surrounding them — like snow on a television. The viewer indicated whether the images were rotating clockwise or counterclockwise. The subject would hear a beep for every correct response.
Each session took an hour and a half. The exercises were taxing, although the subjects took frequent breaks. But after five sessions, the subjects had learned to home in more precisely on the images and to filter out the distracting visual noise. After the training, the older adults performed as well as those 40 years younger, before their own training.
The older participants were also better able to make out letters on an eye chart at reading distance, although not one 10 feet away. The younger students were better able to see the distant eye chart, but not the closer one.
“We think that a behavioral intervention where learning is going on changes brain structure in older adults,” Dr. Andersen said.
In the absence of a disease like glaucoma or changes in the retina and optic nerve, contrast sensitivity is processed by the brain’s visual cortex. This study suggests that certain areas of the brain can be strengthened. “It means the visual system has a high degree of plasticity, even in old age,” Dr. Andersen said.
Dr. Andersen and his colleagues, including Denton DeLoss, a graduate student and the paper’s lead author, say they do not know how long the effects of this modest intervention will last. But an earlier study in which older adults received training to sharpen their ability to discern texture showed that the improvement was sustained for at least three months.
Dr. Andersen said that as people aged, the random firing of neurons in the brain’s visual system increased, creating a kind of internal noise. At the same time, the aging brain struggles harder with external visual noise, such as snowflakes in a blizzard that obscure words on a road sign.
The latest study’s exercises were designed to train adults to filter such external visual noise so they could better discern edges of contrast. “It’s possible that the brain might simultaneously have been trained to reduce internalized noise,” Dr. Andersen said.
Researchers are increasingly focused on perceptual learning, the brain’s ability to discriminate among stimuli — training the ear, for example, to distinguish between Shostakovich and Bartok, or the palate to discern a cabernet sauvignon from a pinot noir. There is also much research on the aging brain. But until now, few scientists have thought to examine the possibilities for improving perceptual learning in older adults.
“These researchers are leading the charge,” Dr. Sekuler said.
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