1. [5] L.A. Riggs: Visual Acuity, Vision and Visual Perception, 321-349, John Wiley & Sons, New York (1965).
2. [6] K. Sagawa, H. Ujike and T. Sasaki: Legibility of Japanese characters and sentences as a function of age, Proceedings of the IEA 2003, 7, 496-499 (2003).