Conveying emotion in robotic speech: Lessons learned

This research explored whether robots can use modern speech synthesizers to convey emotion with their speech. We investigated the use of MARY, an open source speech synthesizer, to convey a robot´s emotional intent to novice robot users. The first experiment indicated that participants were able to distinguish the intended emotions of anger, calm, fear, and sadness with success rates of 65.9%, 68.9%, 33.3%, and 49.2%, respectively. An issue was the recognition rate of the intended happiness statements, 18.2%, which was below the 20% level determined for chance. The vocal prosody modifications for the expression of happiness were adjusted and the recognition rates for happiness improved to 30.3% in a second experiment. This is an important benchmarking step in a line of research that investigates the use of emotional speech by robots to improve human-robot interaction. Recommendations and lessons learned from this research are presented.