A57: eye control af??
+, if you enable it then object tracking is disabled
It means the camera starts autofocusing as soon as the proximity sensor from your viewfinder detects something (your eye but beware other things close to the viewfinder will trigger it too...).
In theory it can speed up the process of getting your target in focus, even before you're ready yourself. In practise, it can be annoying too. Only you can tell if it's helpful for you.