A Descriptive Model of Passive and Natural Passive Human-Computer Interaction.

System invisibility is a common aim for various computing types such as context-aware and ubiquitous computing. We argue that to achieve invisibility, one must examine the user interactions from a user experience point of view. In this paper, we focus on non-intentional human-computer interactions and discuss the term Passive Interaction, starting from its theoretical background. We present a descriptive model where we define Passive Interaction as an interaction initiated by the system without the user's intention that is triggered by a change in the physical or mental state of a user aiming at adjusting the system status to provide a consistent user experience in an ongoing task. Consequently, we define Natural Passive Interaction as a specific case of Passive Interaction in which the system response is undetected by the user. Finally, we present the requirements that must be satisfied for a Passive Interaction to qualify as a Natural Passive Interaction, and we discuss Passive Interaction effectiveness related to system response time followed by examples of real and envisioned cases/scenarios where such interactions can occur.