  As humans, we have a remarkable capacity for reading the characteristics of
objects only by observing how another person carries them. Indeed, how we
perform our actions naturally embeds information on the item features.
Collaborative robots can achieve the same ability by modulating the strategy
used to transport objects with their end-effector. A contribution in this sense
would promote spontaneous interactions by making an implicit yet effective
communication channel available. This work investigates if humans correctly
perceive the implicit information shared by a robotic manipulator through its
movements during a dyadic collaboration task. Exploiting a generative approach,
we designed robot actions to convey virtual properties of the transported
objects, particularly to inform the partner if any caution is required to
handle the carried item. We found that carefulness is correctly interpreted
when observed through the robot movements. In the experiment, we used identical
empty plastic cups; nevertheless, participants approached them differently
depending on the attitude shown by the robot: humans change how they reach for
the object, being more careful whenever the robot does the same. This emerging
form of motor contagion is entirely spontaneous and happens even if the task
does not require it.
