How to use the most of residual hearing is an important problem to every child whose hearing is severely impaired.
This study was attempted to find out how they are using aid in a unselected group of 68 so-called deaf children and to investigate how they should use hearing aid properly and effectively.
The findings considered in this study can be summarized as follows.
(1) There are some children who did not response to pure tone from audiometer through receiver, but responsed to sound from loud speaker in free field with powerful hearing aid. Their hearing loss are supposed above 90dB, and it should be emphasized that exercise and training of hearing is important even in case of these severe hearing impairment.
(2) Typical mobern Japanese hearing aid has so small acoustic gain that it is not so effective to severe hearing loss. They should use more powerfully amplified hearing aid.
(4) Correct and effective using method, should be taught to young hearing aid user and their parents.

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Intravital incubation (for 15 minutes) of the perilymphatic space of the cochlea with substrate (nitro blue tetrazolium) histochemically could demonstrate succinic dehydrogenase activity of the hair cells of the organ of Corti in living guinea pigs. Subsequent surface preparation of the organ of Corti provided good surface specimens for observation of succinic dehydrogenase activity of the hair cells. Twenty guinea pigs of the Hartley strain were used. Fifteen of them were exposed for 8 hours daily to a sound of 4, 000c.p.s. of an intensity of 80dB for 8 days. The other 5 were the control. The threshold of the pinna reflex of the animals was estimated by the audiometer for animals before and after the exposure. One of the experimental animals exposed to the sound showed slight hearing impairment. Histochemically there were no distinct differences in succinic dehydrogenase activity of the hair cells between in the control and experimental animals. Both the inner and outer hair cells contained a large amount of diformazan granules in the supra-, infra- and perinuclear areas of the cytoplasms. There was no remarkable difference in succinic dehydrogenase activity between the upper and lower turns.

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Clinical pictures of the infants with dysacousis and psychosomatics are markedly variegated, and their physical developments are mostly unbalanced. Recently, the authers performed profile-observation on the mental development of the infants with physical deficiency, who are not under the special education.
87 cases with typical abnormal symptoms among 136 cases (0-7 years old), were employed (a case materials).
They were classified into 23 cases with neurotic dysacousis, 30 cases with mental retardation, 21 cases with mental retardation complicated with dysacousis, 10 cases with cerebral palsy, 3 cases with cerebral palsy, 3 cases with cerebral palsy complicated with dysacousis.
The test-method employed were audiometric tests such as startle respons-audiometry, COR-audiometry, play-audiometry, standard-audiometry as well as mental development tests for babies and infants issued from Aiiku Research Laboratory.
In summary, the authors recognized slight, medium and marked features among the cases with main symptom of neurotic dysacousis, and development-profile of deafness as well as the main symptom of mental retardation and cerebral palsy and accompanie with dysacousis. and the authors discussed development-profile on each symptom.

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The experiment was conducted on the use of binaural hearing with two separate hearing aids by six deaf children who had hearing losses greater than 85dB. They had been educated for five years using one aid on a ear, when the first performance was done. It was first time they used two aids. The tests were performed four times from July, 1964 to January 1966. By the word discrimination tests consisted with 40 words. The binaural discriminations were superior to the monaural scores at each time though the later one was not necessarily superiore than the former.
The answers of questionnaire by the mothers of 44 deaf children who had used two hearing aids on each ear for one month to two years, indicated the effectiveness of binaural hearing with two separate aids.

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Using psycho-acoustic methods, hearing threshold of short tones were determind for normal and impaired ear at various duration of test tones. There were significant difference between the normal ear and perceptive types of deafness with regard to their threshold acuities as a function of stimulus duration. In order to describe precisely psycho-acoustic phenomena of hearing, the time factors of test tones should be considered to be important as well as intensity factor of test tones. The psycho-acoustic measurements of hearing threshold of short tones is so simple and conventional that the two factors, time factor and intensity factor of test tones, are obtained simultaneously. The deviations of jugments of threshold responses to short tones was excellently smaller than continuous tones which was now used routinely. The data calculated in this investigations did not completly fit the Gerner-Miller's model (I-I₀)T=K. Several different energy level where the temporal summations was performed, were considered on “σ scale” (a scale of psychology).
The peripheral acoustic-neural mechanism in man was discussed on the results of this psycho-acoustic investigations.

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Air- and bone conduction hearing were followed up on the cases of congenital malformations of the sound conducting apparatus before and after the fenestration surgery.
The cases were classified into three groups; Group I., complete meatal atresia (seven ears), Group II., incomplete meatal atresia (four ears), and Group III., normal auditory canal (six ears), all combined with stapes ankylosis.
Preoperative hearing tests showed worse audio-grams for air as well as bone conduction hearing in normal auditory canal group than in meatal atresia groups. In contrast with those, postoperative audio-grams showed much improved hearing and almost the equal types and levels in all groups.
The mechanisms were discussed on pathological sound conducting systems which caused the differences of preoperative hearing between meatal atresia groups and normal ear canal group.

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