This study was attempted to evaluate the efficiency of hearing aid use of 69 hearing impaired children in a hard-of-hearing class of four schools in Osaka. The results were as follows. a) The factors of acquiring the benefit of wearing hearing aid were: 1) The children who had hearing loss from 60dB to 80dB had the best results. 2) It was necessary to establish a fundamental attitude and ability before the hearing aid. 3) The difference between hearing loss and output to input in 75dB SPL at 1KHz of hearing aid adjusted in the most comfortable listening condition was approximately 30dB in many of subjects. b) The effects of using hearing aids were: 1) There was a slight tendency to have a clear pronounciation in speaking of children who had high socre in aided ear. 2) It is greatly effective to use hearing aid in daily speech conversation. 3) There was no relation between the auditory effect of hearing aid and the school marks.
The absolute thresholds for hearing were measured by small earphone which was calibrated in 2cc coupler in 16 deaf children with and without hearing aids. And the differences of these values at each frequency were compared with the gains of the hearing aid. Theoretically the differences must be corresponded with the gain of the aid, but practically they were not. If difference of 10dB was allowable, 91% of cases showed no differnce of these values.
The quality of sound through a hearing aid in hearing impaired persons was much different from that in normal subjects. Some experiments about agreeable reception and preference for quality of tones were performed. Method: Four different test tones generated through the following circuits were given to normal subjects and hard of hering patients, and the difference between the paired tones was discriminated. The circuits were, 1) A circuit having a peak at 1, 000Hz. 2) A circuit having somewhat a similar characteristic to 1) circuit and having six band pass filters. 3) A circuit having a peak at 2, 000Hz. 4) A circuit having somewhat a similar characteristic to 3) circuit and having six band pass filters. The method of pair comparisons was used. Tones from circuit 1) and 2), 3) and 4) were made pairs for the agreeable reception judgement. For the preference, circuits 1) and 3) were made a pair. Conclusion: As to the agreeable reception, about a half of the normal subjects discriminated the difference of tones but hard of hearing patients was unstable in response and almost failed in discriminating the difference. As to the preference of the quality of tones, normal subjects selected the tone with a peak at 1, 000Hz, whereas the hard of hearing patients selected the one with a peak at 2, 000Hz. These experiments suggested that it was questionable to decide the quality of hearing aid by a judgment by the normal subjects or by the electrophysical characteristics.
In spite of many improvements of hearing aid, the fitting manuals are not yet feasible and each hearing handicapped patients still need particular consideration. And the authors found that shape of audiogram does not always indicate the particular need for a patient, and also speech audiometory may not be helpful in some cases. “A Master Auditory Trainer-MAT” developed three years ago by the authors has adjustable gain 6 band step octave filters and it was caliblated accurately in the sound pressure level, and also contained the ARCs (compression devices). Although the MAT was specially designed for the diagonistic and the auditory training use. And it has been used efficiently to determine the type of hearing aid to meet the individual needs, the authors found some difficulties to apply the MAT's data to hearing aid directly. The difficulties seemed to be due to different circuits and voltage used. Therefore, two different instruments, with same circuits, controls and operating voltage were developed. One of them was called “Hearing Aid Fitting Tester-HK”, which was contained in a desk type metal cabinet, and the other was called “HA-X”, which was built in a small body aid box. In these matched-pair instruments, there were two easy contorolable band filters with a cross-over point, at 750Hz, which could devid the speech frequency range into two parts. With the same handling of MAT, we could easily find the best point in the controls of HK within a few minutes with live or running voice test. And many of our clients much satisfied in fitting their hearing aids with this combination even if they have ordinary aids. With two HKs in a stereophonic training unit and, in a good individual fitting type training unit of the group hearing aid, a new system is nearly accomplished.
Up to May 1972, classes for the hard of hearing in primary schools were housed in 67 schools in our country. The education for children with hearing impairment begins at the earliest practical age. In Japan, however, there are only a few auditory training institutions for pre-school children with hearing impairment. In April 1969, we established a “the Hearing and Speech Clinic for Deaf Infants” at the “Omotoryo” or a domitory for deaf children in Okayama City, supported by the prefectural and national government. In this publication, we report our experience and observations made during a three-year period, and emphasize next points: 1) Such a clinic plays very important part in establishing an early diagnosis and offering guidance to infants with speech returdation. 2) The auditory training of deaf infants is best managed under visiting clinic system. Such handicapped infants need social contacts and mingling with normal children for achieving essential education. 3) Such clinic should be financially unencumbered and probably should be under government support. 4) To attack talents as trainers for such handicapped infants there is a need for establishing the trainers in a more prestigious position.