  How can multiple humans interact with multiple robots? The goal of our
research is to create an effective interface that allows multiple operators to
collaboratively control teams of robots in complex tasks. In this paper, we
focus on a key aspect that affects our exploration of the design space of
human-robot interfaces -- inter-human communication. More specifically, we
study the impact of direct and indirect communication on several metrics, such
as awareness, workload, trust, and interface usability. In our experiments, the
participants can engage directly through verbal communication, or indirectly by
representing their actions and intentions through our interface. We report the
results of a user study based on a collective transport task involving 18 human
subjects and 9 robots. Our study suggests that combining both direct and
indirect communication is the best approach for effective multi-human /
multi-robot interaction.
