Slaying hordes of bad guys -- the more the better -- in fast-paced video games improves vision, a study published Sunday showed for the first time.
Far from being harmful to eyesight, as some had feared, action games such as Counter-Strike, Call of Duty, or Left 4 Dead provide excellent training for what eye doctors call contrast sensitivity, the study found.
Contrast sensitivity is the ability to notice tiny changes in shades of grey against a uniform background, and is critical to everyday activities such as night driving and reading. It often degrades with age.
The findings, published in Nature Neuroscience, reveal a previously unsuspected adaptability in the brain, and could open the way to new therapies, the researchers said.
"This is not a skill that people were supposed to get better at by training," said Daphne Bavelier, a professor at the University of Rochester in New York state and the study's lead researcher.
"It was something that we corrected for at the level of the optics of the eye -- to get better contrast detection you get glasses or laser surgery."
"What we found is that even without this correction you can help your brain make better use of whatever information is received from your retina," she said in a phone interview.
For the study, Bavelier and three colleagues conducted two sets of experiments.
In the first, they compared the contrast sensitivity of hard-core action game players with video game aficionados of the same age who preferred less rapid-fire fare.
In action games, players typically target and shoot figures that pop up suddenly on a computer screen.
The researchers found that the action buffs were 50 percent more efficient at detecting contrast.
But there remained a chicken-or-egg question: had their vision been improved by playing, or did they become action game players because they had better than average contrast sensitivity to start with?
To find out, Bavelier asked two groups of non-action video game players to undergo 50 hours of training. One played a popular point-and-shoot game called Call of Duty, and the other played a game that offered a rich visual experience, but one bereft of action.
"We found that the people in the first group improved by 43 percent, and the other group not at all," she said.
As important, the study also found that the improvement was not transitory. "The positive effect remained months, even years after training, indicating long-lasting gains," she added.
Is there some limit beyond which playing action games loses its positive effect or becomes detrimental? Can you, in other words, have too much of a "good thing"?
"For your visual system, probably not. For your social life, perhaps," said Bavelier.