structural coupling
outer world
auto-reflection
Since human systems are operationally closed and therefore do not dipose of input or output channels, the distance between communicating systems can be problematic. In order to communicate with each other person need media that allows them to communicate with machines and other persons via these machines as well as interfaces that minimize the distance and gap between systems.
 
All H.C.I. efforts therefore have the problem that the linking of two different systems involves handling two differing coding processes in their communication. In other words, "The hardest part of communication is the last four inches." (Frederick Brooks)