  In order to create effective storytelling agents three fundamental questions
must be answered: first, is a physically embodied agent preferable to a virtual
agent or a voice-only narration? Second, does a human voice have an advantage
over a synthesised voice? Third, how should the emotional trajectory of the
different characters in a story be related to a storyteller's facial
expressions during storytelling time, and how does this correlate with the
apparent emotions on the faces of the listeners? The results of two specially
designed studies indicate that the physically embodied robot produces more
attention to the listener as compared to a virtual embodiment, that a human
voice is preferable over the current state of the art of text-to-speech, and
that there is a complex yet interesting relation between the emotion lines of
the story, the facial expressions of the narrating agent, and the emotions of
the listener, and that the empathising of the listener is evident through its
facial expressions. This work constitutes an important step towards emotional
storytelling robots that can observe their listeners and adapt their style in
order to maximise their effectiveness.
