About Face 3: The Essentials of Interaction Design
Optimal design results only when designers have an accurate and complete system model, attain an accurate and complete interaction model, and then design a system interface that reflects an efficient merging of both models.
Kritina Holden • Universal Principles of Design, Revised and Updated: 125 Ways to Enhance Usability, Influence Perception, Increase Appeal, Make Better Design Decisions, and Teach through Design
Enhancements to a product come primarily by watching how people use what exists today, discovering difficulties, and then overcoming them.
Don Norman • Emotional Design: Why We Love (or Hate) Everyday Things
Once the requirements are gathered up, the user experience design team (assuming the company has such a team), is asked to provide the interaction design, the visual design, and, in cases of physical devices, the industrial design.
Marty Cagan • INSPIRED: How to Create Tech Products Customers Love (Silicon Valley Product Group)
Interaction design generally includes the underlying conceptual models