  Our goal is to enable robots to perform functional tasks in emotive ways, be
it in response to their users' emotional states, or expressive of their
confidence levels. Prior work has proposed learning independent cost functions
from user feedback for each target emotion, so that the robot may optimize it
alongside task and environment specific objectives for any situation it
encounters. However, this approach is inefficient when modeling multiple
emotions and unable to generalize to new ones. In this work, we leverage the
fact that emotions are not independent of each other: they are related through
a latent space of Valence-Arousal-Dominance (VAD). Our key idea is to learn a
model for how trajectories map onto VAD with user labels. Considering the
distance between a trajectory's mapping and a target VAD allows this single
model to represent cost functions for all emotions. As a result 1) all user
feedback can contribute to learning about every emotion; 2) the robot can
generate trajectories for any emotion in the space instead of only a few
predefined ones; and 3) the robot can respond emotively to user-generated
natural language by mapping it to a target VAD. We introduce a method that
interactively learns to map trajectories to this latent space and test it in
simulation and in a user study. In experiments, we use a simple vacuum robot as
well as the Cassie biped.
