People need to know that the system has registered an interaction event, such as mouse click, mouse movement, arrow movement, keyboard press, etc.
Where an interaction event is only part of a sequence of commands to a system, or where no explicit user perceptible effect is achieved, people can become anxious that they have not been “heard” by the system, and may repeat the click or movement.
This anxiety can be relieved by giving some feedback — proportionate to the scale of the interaction event and its significance — to confirm to the user that the system has registered the event. Possibilities include, indenting a button, back-lighting a word, changing the shape of the cursor, making an audible click or beep.
For instance, the satisfying “zip’ when a window is rolled up or down in the Mac System 7.1a interface, the simple clicking of the mouse button, the movement of the key when hit by the finger, the “ghost” of the folder as it is closed and “replaced” in its parent folder.
In some work environments, an audible feedback may cause annoyance, so it must be possible for the user to silence it.
Therefore:
Give visual feedback and allow the user to enable audio feedback for every interaction event.
If the computer action that has been initiated by the interaction event is going to take a significant amount of time to complete, then an indication if this should be given — SHOW COMPUTER IS THINKING (#) . . . .