Effects of Speech Level Shift Tested by a Non-Task-Oriented Dialog System on Text Chat Dialog with Users in Japanese: A Pilot Study

Recently, interaction between humans and dialog systems has become increasingly common and sophisticated. Humans establish good relationships with others using various linguistic considerations (e.g., politeness and speech level) in dialog. However, the effect of linguistic considerations used by dialog systems has remained unclear. This study examines the effects of the speech level shift used by a text chat dialog system in Japanese-language user dialog. We designed a rule-based, non-task-oriented text dialog system that controls formal and informal speech levels for Japanese dialog; the effects of a shift in the speech level used by the dialog system were verified through psychological experiments using text chats (n = 134). The speech level control method was constructed with reference to statistical information from the BTSJ Japanese natural conversation corpus and knowledge of linguistic considerations (politeness). The results of the experiment showed that 41.3% of the participants who interacted with the dialog system that shifted the speech level also shifted their speech levels in response. Moreover, a subjective evaluation revealed that participants who noticed the speech level shift of the dialog system felt that this system paid attention to its relationship with the participants. The experimental results suggest that a dialog system can realize dialog in which the user and system both adjust their relationship through dynamic speech level shifts. This study identifies the importance of dynamic speech level shifts, an important factor for expressing politeness, in interactions between humans and dialog systems.