Interaction Design is one of the many facets of User Experience Design. The Encyclopedia of Interaction Design defines it as “shaping digital things for people’s use.” It’s a complex and wide ranging field that covers nearly all aspects of cognition, emotion, and behavior.
It's about designing for the entire interconnected system: the device, the interface, the context, the environment, and the people. According to the Interaction Design Association, Interaction Design “defines the structure and behavior of interactive systems.” Interaction designers strive to create meaningful relationships between people and the products and services that they use, from computers, to mobile devices, to appliances, and beyond.
Interaction Design principles are important to keep in mind as we develop complex applications. Teams that have an understanding of these basic principles will positively contribute to the overall user experience.
We are wired to be sensitive to change. Changes to a layout attract our attention. As long as persistent elements remain in the same place, retain the same appearance, and adhere to the same grid layout and proportions, we do not direct attention toward them until we need them. But when elements move and change appearance without purpose across pages or screens, it becomes immediately noticeable.
If people are asking why something is the way it is, or why it is different, then they've been distracted by the interface. When designs are consistent in appearance and behavior, people are able to focus on their tasks, and they're not distracted by surprising or unexpected changes.
Perceivability invites interaction. Hidden interactions decrease usability and efficiency. People should not need to search for opportunities to interact. They should not guess when interacting, due to confusion or desperation. We should be able to review an interface, and identify where we can interact. Interaction should not depend on luck or random discovery.
Interactions should be easy to learn, and easy to remember. Ideally, people should be able use an interface once, learn it, and remember it forever. Practically, people often need to use an interface at least a few times before they learn it, and then we hope that they will remember what they have learned.
Good interaction design should set accurate expectations about what will happen before the interaction has occurred. We should be able to show people an interface and ask, before they interact, what can you do here? Where can you interact with this? What will happen if you do that? What will be the result, or outcome?
We can set context and expectations by either demonstrating what can be done, such as animations, video, or overlays, or by describing what can be done, such as providing examples or instructions.
Feedback provides acknowledgment of our interactions and information about their outcomes. We use feedback to understand where we are, our current condition or status, what we can do next, and even to know when we are finished.
Feedback should complement the experience, not complicate it. Provide feedback when people need it. It should be noticeable and meaningful. Failure to acknowledge an interaction, or provide feedback that is not noticed, can lead to unnecessary repetition of actions, mistakes, and errors.
Forming a System
The five principles all work together in a system. When interactions are perceivable and noticeable, and their outcomes can be accurately predicted, people will interact with the interface. When meaningful feedback is provided after an interaction, people will understand how their actions led to the outcomes. When people understand the feedback from their interactions, and they learn how the interface works, with continued practice and observation of the interface, their learning becomes stronger.