  As robotic arms become prevalent in industry it is crucial to improve levels
of trust from human collaborators. Low levels of trust in human-robot
interaction can reduce overall performance and prevent full robot utilization.
We investigated the potential benefits of using emotional musical prosody to
allow the robot to respond emotionally to the user's actions. We tested
participants' responses to interacting with a virtual robot arm that acted as a
decision agent, helping participants select the next number in a sequence. We
compared results from three versions of the application in a between-group
experiment, where the robot had different emotional reactions to the user's
input depending on whether the user agreed with the robot and whether the
user's choice was correct. In all versions, the robot reacted with emotional
gestures. One version used prosody-based emotional audio phrases selected from
our dataset of singer improvisations, the second version used audio consisting
of a single pitch randomly assigned to each emotion, and the final version used
no audio, only gestures. Our results showed no significant difference for the
percentage of times users from each group agreed with the robot, and no
difference between user's agreement with the robot after it made a mistake.
However, participants also took a trust survey following the interaction, and
we found that the reported trust ratings of the musical prosody group were
significantly higher than both the single-pitch and no audio groups.
