The system should always keep users informed about what is going on and how it is interpreting the user's input. Feedback should not always be negative by identifying an error situation. The system can also provide positive feedback or partial feedback with continuous updateds as information becomes available.
System feedback should "Speak the User's Language" by restating and rephrasing the user's input to indicate what is being done with it. For example, it is a good idea to give a warning message in case the user is about to perform an irreversible action, such as overwriting a file.
Different types of feedback may need different degrees of persistence in the interface.
Normally, response times should be as fast as possible, but it is also possible for the computer to react so fast that the user cannot keep up with the feedback. Since computers can be too fast indicates the need for user-interface changes to be timed according to a real-time clock rather than being times as an indirect effect of the computer's execution speed.
Feedback becomes especially important in case the system has long response times. In cases where the computer cannot provide fairly immediate response, continuous feedback should be provided to the user in form of a percent-done indicator. As a rule of thumb, percent-done progress indicators should be used for operations taking more than about 10 seconds. Progress indicators have three main advantages:
For operations where it is unknown in advance how much work has to be done, it may not be possible to use a percent-done indicator. Instead, running progress feedback in terms of the absolute amount of work done should be provided.
Informative feedback should also be given in case of system failure. No feedback is almost is the worst possible feedback since it leaves users to guess what is wrong.