Providing the Proper Feedback
To be effective, feedback to the user for an action must occur within certain time limits.
Excessive delays can be annoying, interrupt concentration, cause the user concern, and impair productivity as one’s memory limitations begin to be tested.
System responsiveness should match the speed and flow of human thought processes.
If continuity of thinking is required and information must be remembered throughout several responses, response time should be less than one or two seconds.
If human task closures exist, high levels of concentration are not necessary, and moderate short-term memory requirements are imposed; response times of 2 to 4 seconds are acceptable.
If major task closures exist, minimal short-term memory requirements are imposed; responses within 4 to 15 seconds are acceptable.
When the user is free to do other things and return when convenient, response time can be greater than 15 seconds.
Constant delays are preferable to variable delays.
Dealing with Time Delays
Button click acknowledgement:
o Acknowledge all button clicks by visual or aural feedback within one-tenth of a second.
Waits up to 10 seconds:
o If an operation takes 10 seconds or less to complete, present a “busy” signal until the operation is complete.
Display, for example, an animated hourglass pointer.
Waits of 10 seconds to 1 minute:
o If an operation takes longer than 10 seconds to complete, display:
§ A rolling barber’s pole or other large animated object.
§ Additionally, a progress indicator, percent complete message, or elapsed time message.
Waits over 1 minute:
o Present an estimate of the length of the wait.
o Display a progress indicator, percent complete message, or elapsed time message.
o When a long operation is completed, present an acknowledgment that it is
§ A significantly changed screen appearance.
§ An auditory tone.
o If an operation is very time-consuming:
o Consider breaking the operation into subtasks and providing progress indicators for each subtask.
o Allow users to start a new activity while waiting.
Long, invisible operations:
o When an operation not visible to the user is completed, present an acknowledgment that it is completed.
o A message.
o An auditory tone.
o A long rectangular bar that is initially empty but filled as the operation proceeds.
§ Dynamically fill the bar.
§ Fill it with a color or shade of gray.
§ Fill it from left to right or bottom to top.
Percent complete message:
o A message that indicates the percent of the operation that is complete.
o Useful if a progress indicator takes too long to update.
Elapsed time message:
o A message that shows the amount of elapsed time that the operation is consuming.
o Useful if:
§ The length of the operation is not known in advance.
§ A particular part of the operation will take an unusually long time to complete.
Web page downloads:
o For pages requiring download times greater that 5 seconds, give the user
o something to do while waiting.
o Quickly present, at the top of the downloading page, some text or links.
Blinking for Attention
Attract attention by flashing an indicator when an application is inactive but must display a message to the user.
o If a window, flash the title bar.
o If minimized, flash its icon.
To provide an additional message indication, also provide an auditory signal (one or two beeps).
o Very useful if:
o The window or icon is hidden.
o The user’s attention is frequently directed away from the screen.
Display the message:
o When the application is activated.
o When requested by the user.
Use of Sound
Always use in conjunction with a visual indication.
Use no more than six different tones.
o Ensure that people can discriminate among them.
Do not use:
o Jingles or tunes.
o Loud signals.
Use tones consistently.
o Provide unique but similar tones for similar situations.
Provide signal frequencies between 500 and 1,000 Hz.
Allow the user to adjust the volume or turn the sound off altogether.
Test the sounds with users over extended trial periods.
Use sounds sparingly because they:
o Are annoying to many people, including other users and nonusers in the vicinity.
o Can easily be overused, increasing the possibility that they will be ignored.
o Are not reliable because:
§ Some people are hard of hearing.
§ If they are not heard, they leave no permanent record of having occurred.
§ The user can turn them off
Sounds, sometimes called earcons, are useful for alerting the user:
o To minor and obvious mistakes.
o When something unexpected happens.
o Where visual attention is directed away from the screen and immediate attention is required.
o When a long process is finished.