Playing action-based video games has been shown to improve attentional processing. Li et al. now find that it also induces long-lasting improvements in contrast sensitivity, a basic visual function that commonly deteriorates with age. These improvements do not happen for an equivalent group who played a non-action video game. Contrast sensitivity is one of the main limiting factors in a wide variety of visual tasks, and it is one of the aspects of vision that is most easily compromised. Here is a useful illustration of contrast sensitivity, from an accompanying review of their work (click to enlarge).
Stimulus contrast and tests of visual function - Top, examples of low- (left) and high-contrast (right) sine wave gratings. Simple stimuli such as these are often used in perceptual learning experiments. Bottom left, an example of a Snellen Eye chart used to measure visual acuity. Bottom right, an example of a Campbell-Robson contrast sensitivity function chart. To see your own contrast sensitivity function, look toward the top of the chart, where the white-black modulations should 'blend in' with the gray background. The inverted-U shaped curve that you see indicates that contrast sensitivity is better for mid-range spatial frequencies than for low or high ones. Playing action-based video games improves contrast sensitivity, effectively 'pushing' this curve upwards.