Radio-button options below should have the Fourth option (initial) selected to begin with.
After that, start entering text into the input box. With one or more characters entered, the radio button selection button will start cycling, from First option for 1 char, Second option for 2 chars, and so on, wrapping after each 5. This cycling is based on the length of the input value--not the total number of characters entered. So backspace should cycle the radio button backwards.