  Skilled motor behavior is critical in many human daily life activities and
professions. The design of robots that can effectively teach motor skills is an
important challenge in the robotics field. In particular, it is important to
understand whether the involvement in the training of a robot exhibiting social
behaviors impacts on the learning and the experience of the human pupils. In
this study, we addressed this question and we asked participants to learn a
complex task - stabilizing an inverted pendulum - by training with physical
assistance provided by a robotic manipulandum, the Wristbot. One group of
participants performed the training only using the Wristbot, whereas for
another group the same physical assistance was attributed to the humanoid robot
iCub, who played the role of an expert trainer and exhibited also some social
behaviors. The results obtained show that participants of both groups
effectively acquired the skill by leveraging the physical assistance, as they
significantly improved their stabilization performance even when the assistance
was removed. Moreover, learning in a context of interaction with a humanoid
robot assistant led subjects to increased motivation and more enjoyable
training experience, without negative effects on attention and perceived
effort. With the experimental approach presented in this study, it is possible
to investigate the relative contribution of haptic and social signals in the
context of motor learning mediated by human-robot interaction, with the aim of
developing effective robot trainers.
