## 3 Question-Answer-Response Dialogue Model
### Utterance Selection in Each State
Those numbers were 1 (9%), 8 (73%), and 2 (18%) in one-robot scenario, and were 2 (15%), 9 (69%), and 2 (15%) in two-robot scenario, respectively. ### Caregiver Subjective Impression

Figure 11 shows the averages of the scores of the question to the caregivers, which is whether the participants had talked with the robot more positively than usual. The total average of the scores was 4.92 (SD = 1.89). The average of the scores of the one-robot scenario was 4.55 (SD = 1.86), and that of two-robot scenario was 5.23 (SD = 1.92). There was no significant difference between the scenarios (U = 61.5, \(p=0.568\), [PERSON]'s d = \(-0.186\)). Figure 10: Results of the question to the participants in each scenario. Figure 9: Averages of the user utterance time in each scenario. ## 8 Discussion and Conclusions

### Interpretation of the Results

The total average of the WERs was 0.778. This means that approximately 78% of the words in the utterances of the participants were mis-recognized. In general, it would be too difficult to continue a dialogue with this speech recognition accuracy. Despite the difficult situation, the system continued the dialogues for 12 min 51 s on average. This suggests that the twin-robot dialogue system could sustain a dialogue for a certain time regardless of speech recognition failures. The average of the participant utterance time was 3 min 31 s, which was approximately 27% of the average dialogue time (cf. the average of the robot utterance times was approximately 5 min 51 s). In other words, the ratio of the participant utterance times to the robot utterance time was approximately 3:5. Because the gap between the utterance time of the participants and the robot was not so much, the participants can be considered to have positively participated in dialogue with the twin-robot dialogue system. Regarding subjective impressions, 71% of participants answered that there was nothing strange in the dialogues with the robot. We believe that the system could have provided a dialogue without breakdown for many participants. In addition, the caregivers answered that they felt that the participants had been speaking more positively than usual. Because such positive participation might have involved a novelty effect that none of the participants has spoken to a robot before or an experimenter effect that the participants received special attention in the context of this experiment, we cannot justify whether the system was able to encourage some participants to participate more actively. To clarify the effect of the system on the positive participation, a long-term study is required. In contrast, there was no significant difference between the one-robot scenario and two-robot scenario in each measurement. Therefore, it is still unclear if the use of two robots is effective in improving the user experience of dialogue. Nevertheless, regarding dialogue time, the effect size was medium ([PERSON]'s \(\mathrm{d}=-0.519\)). The results suggested that the presence of two robots might likely encourage elderly people to sustain the talk. ### Effects on the Elderly with Dementia

The caregivers who observed the trial remarked, during an interview after the trial, that participants with dementia appeared to have really enjoyed the dialogue. To comprehend their opinion, we grouped the results of the following question posed to the caregivers, \"Did the participant talk with the robot more positively, comparing to when he or she talk with staffs?\" at the level of dementia (Figure 12). Although two-way ANOVA showed no interaction between groups and scenarios, the graph appears to suggest the trend that participants with severe dementia spoke more

Figure 11: Averages of the scores of the question to the caregivers. actively than usual, in accordance with the observation caregivers made during the trial and confirmed during the interview after the trial. Furthermore, we grouped the participant utterance times precisely as we did for the caregiver impressions (Figure 13).