The interaction theory focuses on designing human-computer interaction in a user-centered way. The following basic principles should be followed to achieve a good interaction design:
Increase visibility
Give feedback
Use affordances
Map intuitively
Design consistently
Use constraints
Allow error prevention and reversal
Reduce memory/cognitive load
Use signifiers
Visibility refers to a simple rule: if the user can not see it, it does not exist. The major functionalities and features should be placed so the user can see all the options at a glance. However, we must take care not to clutter the interface. Therefore, we must achieve a trade-off.
The user should immediately be told what action has been performed and its consequences, if any. Feedback is usually incorporated using dialogue boxes. Critical feedback should be shown as alerts, and more subtle messages should be used to show successful workflow. Feedback should also be given about the current system state. For example, the percentage of a task completed.
An affordance is a relationship between the appearance of an object and how it is used. When an affordance is used, a user can perceive the actions an object can perform by just looking at it - without additional instructions. For instance, if we look at a mug with a handle, we can instantly perceive that it is used for holding it. In user interaction, affordances can be implemented using buttons, icons, input fields, and other elements.
Mapping refers to how controls affect the real world. Good mapping is when the controls are similar to how that action is performed in real life. An example is scroll bars on the screen: a vertical scroll bar moves the page up or down, and a horizontal one moves it towards the left or right, both doing so with just the right proportions and sensitivity. A natural and intuitive mapping should be used for interaction design to help the user efficiently assess the effect of the controls.
Design should be consistent throughout the interface. A share button should do the same thing across different pages. The same colors should be used to highlight similar parts of the interface. In short, the same elements should perform the same functions with the same behavior throughout the interface.
The user should be given only a set of limited options that they can perform or choose. If we leave the available options open-ended, it can confuse the user and introduce errors. Additionally, users can become overwhelmed by the number of possible options if constraints are not used. Constraints like radio buttons and checkboxes can help restrict possibilities.
To avoid errors, the designer should incorporate elements such as warning messages, constraints, and conventions. Confirmation messages should be shown at critical stages, like deleting a file, to prevent accidental errors. If an error occurs, the user should be given the option to undo or reverse it.
The user should not be made to remember trivial things that the interface can. Additionally, the thinking effort a user puts in to perform an action should be kept to a minimum. A typical pattern to reduce cognitive load is to keep it simple and guide the user by hand through the interface. A user’s memory load can be reduced by using breadcrumbs to show a website’s path, for example.
Only the essential information should be displayed in the design. If something does not help the user perform the required task, it is unnecessary to show it. The number of features available on one screen should be kept minimal.
Signifiers signal a user about the actions that can be performed. There is no use in implementing features if they are not apparent to the user—for example, using evident buttons with self-explanatory text.
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