Acknowledgement

First, I would like to express my gratitude to my supervisor Prof. Nobuyoshi Asai for his great assistance in weekly meetings and personal sessions throughout my research. Also, I am grateful to Prof. Kenneth Cranker and prof. Takafumi Hayashi for providing his voice and making voice files. I received great cooperation from members of my laboratory, Mr. Owada, Mr. Otake, Mr. Matsumoto, and Mr. Takahashi. Finally, I am very thankful to my parents for support and encouragement throughout college.