Responding promptly to user input by returning information about what action is underway or completed is a fundamental principle specifically relevant to interaction design. In interactive products, feedback is of critical importance, as it lets the user know that they have engaged with the system successfully, whether by inputting information, initiating an action or process, or completing a task. For example, video applications such as YouTube have a function enabling users to change the volume of a video: as they click and slide along a bar located at the bottom of the video’s window, the bar changes appearance, visualising what the user is doing; meanwhile the volume of the video increases or decreases accordingly. Thus the user receives two types of response (output) – the bar visualisation is the feedback, while the sound variation is the actual outcome of the interaction.
In some cases, the outcome of the interaction is not directly perceivable; in these cases it is even more important that the user receives feedback. For example, if a user transfers money through their online banking service, once the transfer goes through, they should receive confirmation from the system that they have successfully completed that task; the outcome of this interaction is of course the actual money transfer, but the only way for the user to know that the money has actually transferred is via the feedback provided by the service. The main difference between feedback and outcome is that feedback is just an acknowledgement of an interaction, whereas the outcome is the effect of that interaction resulting in a change in the system’s status or in the real world. However, feedback is critical as it enables the user to assess the outcome of their interaction and what steps they need to make next in order to complete a task.