騒音性聴力損失者のコムニケーション障害に関する研究

Abstract

Up to the present social evaluation of the degree of hearing loss is made by the average threshold values for several, pure tones involved in the acoustic range related to speech. This average indicates numerically only a qualitative aspect of the communication capacity. The language used in our daily life is formed by tones of various frequencies and intensities. Accordingly, the degree of actual competence of communication can not simply. be indicated by such average values. Threshold is the sound-level which is just noticeable. Therefore, the scale related to easiness for hearing should be included into the social evaluation on the degree of hearing loss.From the above-mentioned view point, this study was made for clarifying the relationship between the auditory threshold and the most comfortable loudness level (MCL) elicitable by pure-tone and speech audiometry. And more over a classification on 20 monosyllables was made by using the “hard-easy” scale for listening. The subjects were 124 male workers (248 ears) engaged in noisy work-shops. Noise levels in these work-shops were 90 dB (A) or over.The following results were obtained : (1) High positive correlations were found between the threshold at 4000 Hz and those at 3000 and 6000 Hz, and between the threshold at 1000 Hz and those at 500 and 2000 Hz. From these facts, 1000 Hz and 4000 Hz were useful test-frequencies for early detection of noise-induced hearing loss.(2) High positive correlation between the threshold and MCL was found in at each frequency, especially in high frequencies.(3) Inverse correlation was found as significant between the threshold and MCL-threshold. That is, a recruitment phenomenon was observed in workers with noise-induced hearing loss.(4) The auditory threshold at which MCL begins to increase significantly above the normal MCL level was 30 dB at 4000 Hz and 0 dB at the average frequency value (C2+2C3+C4) /4 or (C2+2C3+2C4+C5) /6.The auditory threshold at which the impairment of communication in daily life begins was 50 dB at 4000 Hz, 0 dB at the average value (C2+2C3+C4) /4, and 20 dB at the average value (C2+ 2C3+2C4+C5) /6.(5) Monosyllables listened easily were “A”, “Wa”, “To” and “O”, while those hard of listening were “Ji”, “Ki”, “Ne”, “Su”, “Shi”, “Te” and “Ri”.(6) Monosyllables with which the subjects frequently tended to confused were as follows : “Ha”, “Ta”, “Mo”, “Ba”, “Ga”, “Te” and “Ne”. The confusion was mainly related to the consonant coming at the top of the word.(7) In the examination of articulation of the monosyllables at the minimum intelligible level, “Ni”, “Shi”, “Ga”, “Ki” and “Su” showed higher rates in subjects with normal auditory threshold than in those with hearing loss.(8) In the examination of articulation of the monosyllables at MCL (for sentence), “Ki”, “Su”, “Te” and “Ji” showed higher rate in subjects with normal auditory threshold than in those with hearing loss.(9) In the examination of MCL for monosyllables, those monosyllables which showed the same pattern mentioned above were “Ni”, “Su” and “Ji”, but “Ri” showed significantly lower articulation rate in subjects with hearing loss.