The Material Turn
No matter if we think about interaction design as a design tradition aimed at giving form to the interaction with computational objects, or if we think about interaction design as being simply about user interface design it is hard to escape the fact that the user interface to a large extent defines the scene and the form of the interaction. Without adopting a fully deterministic perspective here it is still a fact that if the user interface is screen-based and graphical and the input modality is mouse-based, then it is likely that the form of that interaction, that is what the turn-taking looks like and what is demanded by the user, is very similar to other screen-based interfaces with similar input devices. However, the design space for the form of interaction is growing fast. While command-based interfaces and text-based interfaces sort of defined the whole design space in the 1970s, the development since then, including novel ways of bringing sensors, actuators, and smart materials to the user interface has certainly opened up for a broader design space for interaction design. But it is not only the range of materials that has been extended over the last few decades, but we have also moved through a number of form paradigms for interaction design. With this as a point of departure I will in this chapter reflect on how we have moved from early days of command-based user interfaces, via the use of metaphors in the design of graphical user interfaces (GUIs), towards ways of interacting with the computer via tangible user interfaces (TUIs). Further on, I will describe how this movement towards TUIs was a first step away from building user interfaces based on representations and metaphors and a first step towards material interactions.