1. World Health Organization (WHO), 1997. Blindness and Visual Disability, Part I of VII: General Information, Fact Sheet 142.
2. Electronic travel aids for visually impaired—a guided tour;Wong,2000
3. A real-time experimental prototype for enhancement of vision rehabilitation using auditory substitution;Capelle;IEEE Trans. Biomed. Eng.,1998
4. Fish, R.M., “Auditory display for the blind”, US Patent No. 3,800,082 (1974).
5. An experimental system for auditory image representations;Meijer;IEEE Trans. Biomed. Eng.,1991