## 4 Discussion  
In Experiment 1, when the quiet vehicle drove in front of the participants while emitting the AVAS sound, none of the participants noticed the sound, even though five participants were aware of the existence of the sound before participating in the experiment. As expected, it was difficult for participants to notice the AVAS sound without having a sufficient opportunity to hear and recognize the sound. In Experiment 2, none of the participants used the AVAS sound to detect the approach of the quiet vehicle when they were required to use only audio information with no visual information. Participants tended to use more familiar sounds, such as the sound of the tires and road noise other than the AVAS sound. In the interview conducted after Experiment 2, four participants answered that they noticed the AVAS sound of the quiet vehicle. However, they did not sense the danger associated with the sound and, thus, did not use the sound to recognize the approach of the quiet vehicle. These results suggest the need for further development of the sound design of the AVAS sound to more clearly alert pedestrians to approaching quiet vehicles and the associated danger.  
The follow-up survey conducted 1 month after Experiments 1 and 2 revealed that some participants noticed the AVAS sound in daily life. This tendency was observed regardless of the change in attitudes toward the AVAS sound. The other participants, who did not notice the AVAS sound in daily life after the experiment, also reported that they recognized a change in their attitudes toward the sound. These changes appeared to result from the design-of-awareness process. The follow-up survey conducted 3 months after  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Participants** & **Q. 1** & **Q. 1-1** & **Q. 1-2** & **Q. 2** & **Q. 3** & **Q. 3-1** \\ \hline A & Yes & More than 10 times &
\begin{tabular}{c} Residential area, and mix of \\ residential and shopping area \\ \end{tabular} & Slightly yes & No & – \\ B & Yes & 1 or 2 times & Residential area & Yes & Yes & Friends \\ C & Yes & 5 or 6 times & Residential area & Yes & No & – \\ D & No & – & – & Yes & No & – \\ E & Yes & 1 or 2 times & Residential area & Neither & No & – \\ F & No & – & – & Not much & No & – \\ G & No & – & – & Neither & No & \\ H & Yes & 1 or 2 times & Residential area & Not much & Yes & Friends \\ I & No & – & – & Slightly yes & No & – \\ J & Yes & 5 or 6 times & Residential area & Slightly yes & No & – \\ K & Yes & 5 or 6 times & Residential area & Not much & No & – \\ L & Yes & 3 or 4 times & Mix of residential and shopping area & Slightly yes & No & – \\ \hline \hline \end{tabular}
\end{table}
Table 6: Results of the follow-up survey conducted 3 months after the experiment.  
Experiment 2 revealed that the number of participants who noticed the AVAS sound in daily life increased compared with the results after 1 month. This might be because as time passed, the participants had more opportunities to encounter quiet vehicles and hear the AVAS sound. The effect of the design-of-awareness process appeared to continue over a long duration and became more apparent with time.  
These results indicate that the design-of-awareness process based on the concept of sound education [14] has the potential to change people's attitudes toward the AVAS sound of quiet vehicles and improve the awareness of the sound in daily life, confirming our hypothesis. This approach may contribute to improving peoples' awareness of quiet vehicles. In addition, some participants talked about the AVAS sound to their friends or family after the experiment, regardless of whether they noticed the sound in daily life. Thus, the design-of-awareness process may also be helpful for improving others' recognition of the AVAS sound of quiet vehicles.