1. Faculty of Education, Shimane University, Matsue, Shimane 690-8504, Japan
2. Graduate School of Natural Science and Technology, Shimane University, Matsue, Shimane 690-8504, Japan
3. Advanced ICT Research Institute, National Institute of Information and Communications Technology, Kobe 651-2492, Japan
4. Graduate School of Informatics and Engineering, The University of Electro-Communications, Chofu, Tokyo 182-8585, Japan