Authors: Philip Kortum In the early 1960s, Douglas Engelbart [1] first introduced the notion of "knowledge in the world" versus "knowledge in the head" for computer interfaces—an idea that was later formalized and popularized by Donald Norman in his seminal book The Psychology of Everyday Things. From an interface design standpoint, knowledge in the world simply means that the controls you need are visible, and the identification and operation of these controls can be done through recognition ra...