  In human-robot interaction (HRI), we study how humans interact with robots,
but also the effects of robot behavior on human perception and well-being.
Especially, the influence on humans by tandem robots with one human controlled
and one autonomous robot or even semi-autonomous multi-robot systems is not yet
fully understood. Here, we focus on a leader-follower scenario and study how
emotionally expressive motion patterns of a small, mobile follower robot affect
the perception of a human operator controlling the leading robot. We examined
three distinct emotional behaviors for the follower compared to a neutral
condition: angry, happy and sad. We analyzed how participants maneuvered the
leader robot along a set path while experiencing each follower behavior in a
randomized order. We identified a significant shift in attention toward the
follower with emotionally expressive behaviors compared to the neutral
condition. For example, the angry behavior significantly heightened participant
stress levels and was considered the least preferred behavior. The happy
behavior was the most preferred and associated with increased excitement by the
participants. Integrating the proposed behaviors in robots can profoundly
influence the human operator's attention, emotional state, and overall
experience. These insights are valuable for future HRI tandem robot designs.
