## 3 Question-Answer-Response Dialogue Model
### Utterance Selection in Each State
As such, the system repeats selecting and executing an utterance according to a speech recognition result and its own behavior execution. A social-conversational robot developed by VSTONE, CommU, was used as the dialogue partner in our system. This robot is desktop sized at 304 mm high, 180 mm wide, and 131 mm deep, weighing 938 g. CommU has three degrees of freedom (df) for its waist, 3 df for its neck, and 2 df for each eyes. The robot has two LEDs in its cheeks. The robot controller was a software server, which received a command, such as \"speak\" or \"nod\". The robot controller controlled the robot according to a received command. Figure 4: The system architecture. Figure 3: Hardware components of the system and the connections between them. ## 6 Field Trial

### Purpose

We conducted a field trial in a nursing home. There were two purposes for this field trial. The first was to investigate whether the twin-robot dialogue system can sustain a coherent dialogue with elderly people for a certain time and the second was to evaluate whether the system can provide good user experience of a dialogue. ### Participants

Thirty elderly residents in a nursing home participated in the trial: 26 females and 4 males. They were native Japanese speakers. Their average age was 86.3 years (SD = 7.5). According to caregivers, 13 participants had no dementia, 4 had mild dementia, and the other 13 had advanced dementia. The participants were recruited by caregivers of the nursing home. Before the trial, we explained the purpose and the procedure to the caregivers and asked them to recruit candidates who would like to participate in the trial. We sent an instruction document of the trial to their families and asked the families to fill out a consent form. The consent form had been approved by the ethical committee of Osaka University. The candidates whose families agreed that they should participate in the trial became the participants. Furthermore, two caregivers participated in the trial to observe participants' behavior. ### Scenarios

To achieve the purpose, it was desirable to design an experiment that could clarify two basic research questions: Whether or not the system has the question-answer-response dialogue model, and whether a single robot or two robots engage in a dialogue. However, without the question-answer-response dialogue model, it was obvious that the elderly could not continue a dialogue with the system. The reasons are as follows: the chatbot model commonly used in non-task-oriented chat systems generates responses based on the results of speech recognition. When speech recognition fails, the chatbot model generates a response that does not match the context of the dialogue. Since speech recognition frequently fails during a dialogue with elderly people, the system with the chatbot model would give unrelated responses in the dialogue in most cases. Therefore, we designed scenarios depending on whether only a single robot or two robots participate in a dialogue, which are as follows:

1. **One-robot scenario**. One robot participated in a dialogue. The robot performed tasks according to the question-answer-response dialogue model (see Section 3). 2. **Two-robot scenario**. Two robots participated in a dialogue. The robots performed tasks according to the question-answer-response dialogue model (see Section 3). They take turns according to the rules described in Section 4. The field trial was a between-participant design. The participants were assigned to each scenario in such a way as to balance the dementia level of participants in of each scenario as shown in Table 2. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Cognitive Capacities**} & \multicolumn{2}{c}{**Scenario**} & \multirow{2}{*}{**Total**} \\ \cline{2-3} \cline{4-4}  & **One-Robot** & & **Two-Robot** \\ \hline Noting or mild & 6 & 6 & 12 \\ Severe & 5 & 7 & 12 \\ Total & 11 & 13 & 24 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Distribution of participants’ cognitive capacities.