## 5 Discussion
### User Impressions of Text Dialog System  
Among the conditions, there were no significant differences in evaluation items Q1 to Q3, which aimed to evaluate the human-like characteristics. The average score for all conditions was approximately 5 points, indicating that the dialog system was evaluated as human-like by the experimental participants. The human likeness of a dialog system is an important evaluation index for the system and is considered significant in live dialog system competitions [42]. In previous studies [8; 27; 37; 38], a significant correlation was observed between the dialog strategies used by dialog systems and their perceived human likeness. These studies [8; 37; 38; 39; 40] considered the speech level in addition to applying politeness strategies (such as jokes, compliments, and apologies) based on politeness theory [21] to  
Figure 3: Impression evaluation results of text dialog experiments. The error bars represent the standard error. the design of the dialog systems. Therefore, the differences between the experimental conditions were further emphasized compared to this study. These findings suggest that differences in the speech level and politeness strategies may need to be combined to change the impressions regarding the human likeness of the dialog system significantly through the design of language expressions. Moreover, many previous studies [8, 10, 11, 12, 13, 38] focused on text-based chat with communication robots and virtual agents, which may affect the impressions of dialog systems depending on their modality. The emergence of ChatGPT [53] in recent years has drawn attention to text-based dialog between humans and dialog systems. Thus, research on the design of dialog systems that focus on text-based chats will become increasingly important in the future. In this experiment, a rule-based method was employed to control the utterances of the dialog system. In recent years, extensive research has been performed on large language model-based dialog systems; however, rule-based methods are also widely used in dialog systems for services provided by companies [54]. Although this research does not provide state-of-the-art engineering techniques, we believe that the speech level shift module of the dialog system presented in this paper can be applied to existing rule-based dialog systems, such as those employed by companies. By employing a rule-based system, the speech of the dialog system during the experiment can be easily controlled, while the participants in the experiment can speak freely. Some experimental paradigms, such as the Wizard of Oz approach, do not require autonomous systems; however, psychological experiments using rule-based dialog systems, such as the experiments performed in this study, can be conducted to verify the psychological effects of speech level shifting used by a dialog system in a situation similar to a practical dialog system use case. The shift in the speech level was rated significantly higher for Q4 and Q5, which were the items that indicated whether the participants were aware of the speech level changes. This result demonstrates that the participants perceived the speech level changes in the system more strongly under the condition in which the speech level was deliberately shifted. In contrast, there was no significant difference in Q6. As the mean score for Q6 was higher than four under all experimental conditions (i.e., one-sample test, \(ps<0.01\), and stochastically significant following the Bonferroni multiple-comparison correction), it was assumed that the participants used the speech level of the dialog system as a reference, despite no significant difference in the degree to which this was the case across all conditions. No significant differences were observed between Q7 and Q8, which were the items that indicated a breakdown of the dialog. Therefore, there were no significant differences in the degree of dialog breakdown among the experimental conditions.