*3.2. Transition Rules*

The state transition diagram is shown in Figure 2. Table 1 shows the transition rules for each state. The system transforms from one state to another when it receives some events. In this study, we defined three events: an event in which a robot completed an utterance (Robot Utterance Completion: RUC), an event in which the system recognized user utterance (User Utterance Recognition: UUR), and an event in which user utterance has not been recognized for a certain period of time (Timeout: TO).

The reason for separating the backchannel state from the comment state is to deal with a situation where a user remained mute. In general, when a user answered something, the robot should provide a backchannel like "I see" or "uh-huh" to show that the robot is listening to the user. However, when a user does not answer, the robot should not provide any backchannel because the backchannel would make the user feel strange. At that time, the system skips the backchannel state and transitions to the comment state as shown in the state transition diagram (Figure 2).

**Figure 2.** State transition diagram Of a dialogue with an elderly person.

**Table 1.** State transition table of the state transition diagram. The events are abbreviated as follows: RUC: Robot utterance completion, UUR: User utterance recognition, and TO: User utterance timeout.


Listing 2 is selected.
