## 4 Experiment
### Experimental Conditions  
Participants in the experiment were international students enrolled at Tohoku University and were recruited through a bulletin board on campus. There were no restrictions on age range or English ability, but we explained that the dialogue would be conducted in English and asked only those participants who self-evaluated themselves as having sufficient English conversation skills to participate. For the definition of experimental parameters, we needed 24 participants to obtain a statistical power of 0.8 and an effect size of 0.8. Thus, we invited 25 participants (18 males and 7 females) to the experiment. Of these, 13 participants had experience using chatbots. Not all of the participants were native speakers of English; we asked the participants to choose their self-evaluation of English fluency among \"beginner\", \"intermediate\", \"fluent\", and \"advanced\". As a result, no participants were beginners, five were intermediate, five were fluent, and fifteen were advanced. The procedure of the experiment was as follows:  
* We explained the purpose and procedure of the experiment to the participant.
* We asked the participant for a pre-dialogue questionnaire (Table 6).
* The participant held four rounds of dialogue with the agent. In each round, a participant conversed with the ECA about one particular artwork.
* After each conversation, the participant answered the questionnaire (Table 7) evaluating the current dialogue.
* After four rounds of dialogue, the participant answered the post-dialogue questionnaire (Table 8).  
The order of the response delay and combination with the artwork are shown in Table 9. The order was determined so that the different participants experienced different orders and combinations of artworks, response delays, and the presence of emotion. Overall, each parameter was balanced.  
During the conversation, they asked the agent questions about the displayed artwork for as long as they wanted. The agent's response delay was controlled with a minimum threshold so that the agent waited until the timer had finished. The response delay was set to 500, 1000, 1500, and 2000 ms because most of the response delay in a conversation isbetween 500 and 2000 ms [50]. The specific response delay was achieved by inserting an artificial delay after preparing the ECA's response speech.  
When the ECA was in the \"with-emotion\" condition, the ECA changed its facial expression according to the method explained in the previous section. In the \"without-emotion\" condition, the ECA's face expressed a neutral emotion.  
\begin{table}
\begin{tabular}{l l} \hline Q1 & Gender \\ Q2 & Are you familiar with the concept of a chatbot? (No, I don’t know what a chatbot is./I don’t have much knowledge about it./Yes, I am familiar with the concept.) \\ Q3 & Have you already used a chatbot? (Never used before, Seldom use, Frequently use) \\ Q4 & How would you rate your English level? (Beginner, Intermediate, Advanced, Fluent) \\ \hline \end{tabular}
\end{table}
Table 6: Questionnaire before the conversation.  
\begin{table}
\begin{tabular}{l l} \hline Q1 & Animation \\ Q2 & Conversation skill of the chatbot (Flow of the conversation, phrasing) \\ Q3 & Information accuracy (Does the agent’s answer correspond to your question?) \\ Q4 & Interactivity (Is the agent responsive to your inputs?) \\ Q5 & Interface (Layout, Visibility) \\ Q6 & Naturalness of the conversation (Does the agent look human-like when conversing?) \\ Q7 & Responsiveness (How fast does the agent answer back?) \\ Q8 & Overall satisfaction \\ Q9 & Usability (Ease of use) \\ Q10 & Visual aspect (Graphics) \\ \hline \end{tabular}
\end{table}
Table 7: Questionnaire after each round of conversation (answered on 5-point Likert scale).  
\begin{table}
\begin{tabular}{l l