Here's the first version (with small arrows):
And here's the second version (with larger arrows):
You'll notice that each AdSense ad has a set of arrows located at the bottom, on left-hand side of the ad. By clicking these arrows, your site visitors can "actively scroll" back-and-forth through the ads to see more AdSense ads that they may be interested in.
Obviously, no word yet on how this actually affects AdSense CTR (click-through rate), but I must say that it's an enhancement that may very well help to increase your AdSense earnings. Guess we'll just have to wait and see!