The purpose of this study was to investigate psychological characteristics of the series of approximation to Japanese. Two kinds of the series of approximation were experimentally made by the method which was quite similar to that of Shannon-Miller's guessing technique. The orders of both syllable and word-approximations were 0th, 2nd, 3rd, 4th, 5th, 6th, 7th, and text series. The text series means a series of meaningful syllables or words quoted from magazines and novels.Experiment 1. Syllable-approximation and intelligibility.(A) Procedure: 12 undergraduate students were asked to listen to the auditory stimuli which were given under the masking white noise at the rate of one syllable per second. Five different orders of approximation which consisted of 20 syllables were used as the stimuli. The level of noise was controlled. The S-N ratios were -8, -4, 0, +4, +8, in db.(B) Results: The intelligibility of syllables under the condition of the masking tends to increase with the ascending order of approximation (p 0.99; see Fig. 4).Experiment 6. Syllable-approximation and eye-voice span.(A): 10 students were asked to read the material consisting of 24 letters. While the subject was reading aloud, the light was suddenly extinguished; he was required to continue saying as many which he had seen as possible.(B): The eye-voice span expands in accordance with the order of approximation (p<0.01; see Fig. 5).