How does a spontaneously speaking conversational agent affect user behavior?

This study investigated the effect of synthetic voice of conversational agent trained with spontaneous speech on human interactants. Specifically, we hypothesized that humans will exhibit more social responses when interacting with conversational agent that has a synthetic voice built on spontaneous speech. Typically, speech synthesizers are built on a speech corpus where voice professionals read a set of written sentences. The synthesized speech is clear as if a newscaster were reading a news or a voice actor were playing an anime character. However, this is quite different from spontaneous speech we speak in everyday conversation. Recent advances in speech synthesis enabled us to build a speech synthesizer on a spontaneous speech corpus, and to obtain a near conversational synthesized speech with reasonable quality. By making use of these technology, we examined whether humans produce more social responses to a spontaneously speaking conversational agent. We conducted a large-scale conversation experiment with a conversational agent whose utterances were synthesized with the model trained either with spontaneous speech or read speech. The result showed that the subjects who interacted with the agent whose utterances were synthesized from spontaneous speech tended to show shorter response time and a larger number of backchannels. The result of a questionnaire showed that subjects who interacted with the agent whose utterances were synthesized from spontaneous speech tended to rate their conversation with the agent as closer to a human conversation. These results suggest that speech synthesis built on spontaneous speech is essential to realize a conversational agent as a social actor.