  Albrecht and Stone (2018) state that modeling of changing behaviors remains
an open problem "due to the essentially unconstrained nature of what other
agents may do". In this work we evaluate the adaptability of neural artificial
agents towards assumed partner behaviors in a collaborative reference game. In
this game success is achieved when a knowledgeable Guide can verbally lead a
Follower to the selection of a specific puzzle piece among several distractors.
We frame this language grounding and coordination task as a reinforcement
learning problem and measure to which extent a common reinforcement training
algorithm (PPO) is able to produce neural agents (the Guides) that perform well
with various heuristic Follower behaviors that vary along the dimensions of
confidence and autonomy. We experiment with a learning signal that in addition
to the goal condition also respects an assumed communicative effort. Our
results indicate that this novel ingredient leads to communicative strategies
that are less verbose (staying silent in some of the steps) and that with
respect to that the Guide's strategies indeed adapt to the partner's level of
confidence and autonomy.
