The examinations of the CROS (Contralateral Routing of Signals) type hearing aid were performed under a number of listening conditions, both advantageous and disadvantageous, in order to determine whether the relative merits of the instrument could be demonstrated in the laboratory. The listening conditions were designed by various combinations of the following three parameters: i) the origination of test sound to the bad ear. ii) the presentation of a background with voice babble. iii) the use of hearing aids. The acuity of the sound localization was measured by the speaker system. The subjects for the investigation were 38 listeners with unilateral hearing impairments, which were classified into two groups by their hearing acuities of the better ear. 1) The unaided scores in case of the indirect loudspeaker were reduced by 6% in quiet and by about 20% in voice babble, due to the shadow effect of the head. 2) Under aided conditions, this shadow effect was covered by the hearing aid, but the discrimination score was poorer than under unaided condition in case of the direct loudspeaker. 3) The aided discrimination scores to the speech delivered from the side of the poorer ear were about 5% better in quiet, and about 10% in voice babble than unaided scores. These advantages were mostly found in the group, which had the mild deafness in the better ear. 4) The localization of the sound source under aided condition was deviated to the side of the better ear, as same under unaided, however, a few improvement was shown by means of the difference of tonal timbre.
Comparing the effectiveness of nonlinear amplified hearing aid, S. S. B. peak clipped hearing aid and of linear amplified hearing aid in the perceptive deaf patients the following conclusions were obtained: 1. Nonlinear amplified hearing aid was more effective than the linear amplified hearing aid. Majority of the patients preferred nonlinear amplified hearing aid because it had no impulsive tone. But confusion was not reduced. 2. The patients agreed that the S. S. B peak clipped hearing aid was more intelligible than the linear amplified hearing aid. The higher discrimination score was obtained by the S. S. B clipped hearing aid, and confusion of consonants (/k/, /t/, /h/, /s/, ) was lowered.
In order to get proper knowledge of hearing aid fitting, we investigated hearing loss level, school attendance and the state of hearing aid usage of hearing impaired children who have residual hearing to some extent. Results of this investigation revealed that it appeared to be satisfactory usage of hearing aid if aided threshold by means of hearing aid was able to be reformed to 30-40dB sensation level in the frequencies of 500Hz, 1, 000Hz, 2, 000Hz within 40dB of acoustic gain.
The characteristics of frequency response of hearing aids were generally restricted in many cases by microphone in the lower frequency rang and by earphone in the higher. Several kinds of hearing aids having superior characteristic in the lower frequency have appeared in the market recently. This was because of the fact that the microphones have become better in quality and smaller in type. Increment of information as well as possible to give to the people who were hard of hearing through hearing aid the natural sound have been considered by the authors, and a new type of earphone which have much better quality in the higher frequency has been made on trial. It was also ascertained that the earphone have much better characteristics for the ears with nomal hearing. The result obtained by people of hard of hearing on the new earphone was as follows: (1) There was a difference in response obtained between the real and artificial ear (2cc coupler). But among the artificial ears, the coupler was similar to the real ear that earphones with tips attached were determined the characteristics (directect cavity). (2) The new earphone showed a good result at a quiet environment, but was not good in many cases of people of hard of hearing at the noisy place.
Hearing aid is adapted for the improvement of hearing loss in both adult and children with hearing disturbance. But the significance of adaptation of hearing aid is quite different between adults who have already perceived a sound and children who perceive a sound for the first time through hearing aid. In the present time, hearing aid is usually adapted to children who were diagnosed as the deaf. There are still unsettled problems how to use hearing aid for deaf children. Therefore, children in better hearing class or speech hearing clinic were examined for hearing aid effect to the pure tone. Speech audiometry was also examined under various conditions such as with hearing aid to contralateral ear or both ears and with different types of hearing aid and so forth. In the cases of a long term adaptation of hearing aid, the patients become gradually accustomed to wear hearing aid which they use, and unilateral ears with hearing aid also become accustomed to the sounds. Therefore, it is important for the patients to use hearing aid of good quality from the beginning. Speech discrimination score was not improved in 20 children who were examined for the effect of biaural hearing aid adaptation. The reason of above unimprovement is considered to be that they were not accustomed to biaural hearing aid adaptation. Therefore, in the cases of hearing loss nearly same extent in both ears, children should be trained with binaural hearing aid adaptation.
The hearing aid performance in 65 hearing impaired children who are now in 4 hard-of-hearing classes in Osaka was measured by JIS standard method and by reference to ASA or New HAIC standard method of the electroacoustical characteristics of hearing aids. The following results were obtained. The deficiency of maximum gain and the poorness of volume control were found in an approximately half of the children. It was noticeable that 5 hearing aids were not well operated or had a bad operating condition. Hearing aid user should take both audiological examination and physical performance test of hearing aid periodically.
1) We are not only using hearing aids to hard of hearing children but also to the severely deaf children in the early stage. 2) As a rule, we use a single hearing aid in one ear, but for the children whose hearing impairment is not determined in either of the right or left ear an ear-piece in each ear connected to a hearing aid with Y-code is preferable. 3) As it is difficult for us to determine the suitable volume after studying the research done by Dr. Ogura and others we determined that 70phon input is the optimum volume to bring remarkable reaction. 4) From the inquiries of using hearing-aid of 32 subjects, the following findings were obtained. a) Within a month 70% of children could tolerate wearing hearing aid, and within three months, the effect of hearing aid could be obtained. b) In profoundly acoustically retarded children, hearing aids are effective in the raising of the intensity of their voice. 5) In the future, the application of the EEG, play audiometry, speech audiometry and characteristic test of hearing aids is necessary for the investigation of the optimum volume.
In patients who had been examined at the National Center of Hearing and Speech Disorders during two years from January 1964 to December 1965, 246 with a sensorineural or mixed type of deafness who previously wore or had worn hearing aids were selected in order to gather the information concerning indication and the actual use of hearing aids. Although the age of the patients varied from one to seventy years, approximately 60% of the patients had begun to wear their aids at preschool ages. Sixty-three percent of the patients wore their aids all the time, 12% only occasionally, and 25% did not accept or rejected their aids by the following reasons: uncomfortable or too noisy; no value of the aids; felt shame at wearing their aids; felt a pain in the ear or in the head. The patients making maximum use of hearing aids were seen more in the group of the profoundly deaf patients than in each group of the patients with mild and moderate deafness. Finally, based upon the facts that approximately 40% of the patients who wore their hearing aids at all times were extremely profoundly deaf and especially the aids were of much value in developing speech and language in young deaf children, the authors insisted in terms of rehabilitation and habilitation it is faulty discrimination that doctors or the proper authorities do not provide extremely profoundly deaf patients with hearing aids for no other reason than that the aids are almost useless to hear speech.