Mobile robots are already applied in factories and hospitals, merely to do a distinct task. It is envisioned that robots assist in households soon. Those service robots will have to cope with several situations and tasks and of course with sophisticated human-robot interactions (HRI). Therefore, a robot has not only to consider social rules with respect to proxemics, it must detect in which (interaction) situation it is in and act accordingly. With respect to spatial HRI, we concentrate on the use of non-verbal communication. This chapter stresses the meaning of both, machine movements as signals towards a human and human body language. Considering these aspects will make interaction simpler and smoother.

An observational study is presented to acquire a concept of spatial prompting by a robot and by a human. When a person and robot meet in a narrow hallway in order to pass by, they have to make room for each other. But how can a robot make sure that both really want to pass by instead of starting interaction? This especially concerns narrow, non-artificial surroundings. Which social signals are expected by the user and on the other side, can be generated or processed by a robot? The results will show what an appropriate passing behaviour is and how to distinguish between passage situations and others. The results shed light upon the readability of signals in spatial HRI.