  We propose CASPER (ChAt, Shift and PERform), a novel dialog system consisting
of three types of dialog models: chatter, shifter, and performer. Shifter,
which is designed for topic switching, enables a seamless flow of dialog from
open-domain chat- to task-oriented dialog. In a user study, CASPER gave a
better impression in terms of naturalness of response, lack of forced topic
switching, and satisfaction compared with a baseline dialog system trained in
an end-to-end manner. In an ablation study, we found that naturalness of
response, dialog satisfaction, and task-elicitation rate improved compared with
when shifter was removed from CASPER, indicating that topic shift with shifter
supports the introduction of natural task-oriented dialog.
