## 3 Question-Answer-Response Dialogue Model
### Utterance Selection in Each State
### Procedure

The procedure was as follows: A caregiver escorted a participant to a place of trial (Figure 5). The caregiver had the participant sit down on a chair in front of the robot. If the participant was using a wheelchair, the caregiver put the participant with the wheelchair in front of the robot. After escorting, the caregiver moved to a position behind the participant. Thus, the caregiver was invisible to the participant during the trial. Then, a controller greeted the participant and explained the task. The instruction was as follows: \"This robot starts to talk to you in a little while. Please talk with it.\" After the instruction, the controller started the system and the robot started a dialogue. As the participants were native Japanese speakers, the field trial was conducted in the Japanese language. The procedure that a caregiver takes an elderly person to the robot, encourages him or her to talk with the robot, and watches him or her from behind would be reasonable at least in the phase of introducing the robot system. The dialogue continued following the flowchart of Figure 6. The robot said the introduction first. Next, the robot started a dialogue. In every 5 min during the dialogue, the robot asked the participant whether to continue the dialogue or not. When the participant gave a positive answer, the robot continued the dialogue. Otherwise, a negative answer ended the dialogue. Here, we should note an inappropriate case caused by speech recognition errors. If the robot recognized that the participant answered positively even though the participant actually answered negatively, the robot would have continued the dialogue. Because such a situation must be avoided, an experimenter force-quit a program for a dialogue as soon as possible. Considering the burdens of a participant, we limited the dialogue time to 15 min even if the participant would like to continue. The dialogue was recorded by video cameras. The caregiver had observed the dialogue and filled out in a questionnaire about the participant behavior. When the dialogues ended or were force-quit, the caregiver took the participant to a place away from the robot. Then, an interviewer asked the participant a simple question. After that, the caregiver took the participant back to his or her room, and then escorted the next participant to the place of trial. Figure 5: Twin-Robot dialogue system that talks with an elderly person. ### Dialogue Contents

The number of questions we created was 55, which enabled a dialogue to run for approximately 27 min because it required approximately 30 s in the cycle for the robot to ask a question, receive an answer from the user, and respond to the answer. The details are shown in Table 3. The questions, backchannels, and comments were created by an expert in robot speech creation and elderly care. ### Measurements

We measured the following values: word error rate (WER), dialogue time, user utterance time, and subjective impressions of the participant and caregiver. #### 6.6.1 Word Error Rate

WER is a typical metric of the accuracy of speech recognition [58]. In this experiment, the WER is for errors that occur when the robot recognizes the participant's speech. The WER was calculated as follows:

\[WER=(S+D+I)/N \tag{1}\]

Figure 6: Flowchart of a dialogue in the trial. \begin{table}
\begin{tabular}{l c c} \hline \hline
**Topic** & **Number** & **Example** \\ \hline Childhood & 16 & “Where did you usually play?” \\  & & “What toy did you want?” \\  & & “Did you like to go to school?” \\ \hline Travel & 20 & “Do you like travel?” \\  & & “Where have you traveled so far?” \\  & & “What was the best food you have had in travel?” \\ \hline Health & 19 & “Have you had severe illness so far?” \\  & & “Do you like walking?” \\  & & “Do you have food you eat for health?” \\ \hline \hline \end{tabular}
\end{table} 
Table 3: A part of the questions we prepared for the trial. where \(S\), \(D\), \(I\), and \(N\) are the number of substitutions, deletions, insertions, and words in the reference, respectively.