Cochlear microphonics (CM) and action potential (AP) were measured in animals in which labyrinths were damaged by injection of the various kinds of solution into the facial nerve through the stylomastoid foramen. The results obtained were as follows: 1) After the injection of tetracycline and hydrochloride, the CM and AP waves were not recorded, even applying the maximal sound stimulus. 2) After the first injection of antigen into the sensitized rabbits, CM amplitude was markedly increased at 4KHz, while increased slightly at 0.5KHz. After the repeated injections, caloric response was reduced and the CM and AP amplitude decreased or did not show response to the sound stimuli of the 20dB above VDL in both frequencies. The CM and AP amplitude, however, recovered to the same threshold as before the first injection limits 24 hours after the first procedure. Histopathological findings of the organ of Corti after the injection of tetracycline and hydrochloride revealed degeneration, but no remarkable change was seen in immunologically treated cases. It is thought that these electrophysioiogical phenomena induced by the injection of antigen into sensitized animals were resulted from the antigen-antibody reactions in the autonomic nerve and microcirculations in the cochlea.
With regard to play audiometry (C. O. R. -test, and peepshow test) the procedure, applicable age, reliability and threshold of children who consult to this center from 1972 to 1974, were studied and the following results were obtained. 1) Applicable age for C. O. R. test to measure the threshold was from 1.5 to 3 years of age, and that for peepshow test was above 2.5 years of age. 2) In the cases the threshold was not measured at first time in children under 2 years old, by repeating test the threshold was mostly decided by peepshow test. 3) As the threshold of hearing impaired children were unreliable by only one test, they should undergo the careful measurement of threshold by repeated tests.
At the beginning of evoked response audiometry, the guide pattern of evoked response was selected from the responses to tones of the highest intensity or photic stimuli. The averaged EEG tracings were then superimposed on the guide pattern, and the presence or absence of evoked response was determined by our criteria: 1. More than two components can be detected. 2. P2 latency is within ±50msec of that of the guide pattern. 3. The response can be differentiated from the successive noise. 4. The peak amplitudes of 60 averages are larger than those of 30. Guide pattern, response components, latencies, background noise and the growth of response by averaging were discussed.
An attempt was made to develop a speechreading test to evaluate the combined effects of speechreading and listening with a hearing aid on the comprehension of speech. The test materials consisted of twenty-five homophenes and ten short sentences. The test was presented to twenty-five adults with normal hearing, four adults with severe hearing loss, and two hearing-impaired children under three conditions; speechreading without the use of a hearing aid, with the use of a hearing aid but without watching the speaker's lips, and a combination of speechreading and the use of a hearing aid. It was intended to eliminate the effects of practice brought by repeating the speechreading test by using the homophene word list, while the sentence test was used to evaluate the language ability of the subjects. The results obtained from our test demonstrated that the test using homophenes is valid to evaluate the combined effects of speechreading and listening with a hearing aid, and the sentence test is adequate to examine the language ability.
Screening audiometry for school-age children was administered to the young children under school-age, and the following four points were discussed: adequacy of the screening level of 20dB (JIS-1956), possibility of performance of screening test for the young children, the time of screening for each, and the number of normal hearing children who did not pass the screening test. Mean threshold hearing at 1, 000 and 4, 000Hz of 71 normal hearing children of three, four and five years of age was under 20dB which was similar to those of school-age children and adults. Screening test performed with the hearing level of 20dB at 1, 000 and 4, 000Hz was administered to 176 children from three to five years of age. Ninety-three percent in three-year-old, 97% in four-year-old and 99% in five-year-old children could tolerate the test. Percentage of normal hearing children who did not pass the screening test was 30% in three-year-old and 19% in five-year-old children, and these showed significant difference from those in the school-age children. Almost all of three and four-year-old children could finish the test for less than two minutes. We inferred from these results that the screening audiometry for school-age children could be administered to the young children from three to five years of age.
Two cases of hearing disorders with progressive muscular atrophic diseases were reported. The case 1 is an 11-year-old boy with facio-scapulohumeral type of muscular dystrophy, whose audiogram showed the sensorineural type of bilateral deafness with gradual form of high tone loss. The case 2 is a 29-year-old female with congenital multiple arthrogryposis complaining of progressive hearing impairment of both ears. The audiogram showed sensori-neural deafness. Her hearing acuity became worse as the muscular atrophy proceeded. The hearing impairment of both cases might be due to the pathological change in the inner ear because they had recruitment phenomena and bone conduction disorders.
The early components of the auditory evoked response averaged from the scalp were first reported by Sohmer et al. and also Jewett et al. These authors speculated that the source of the response was from the brain stem. In this study, the possibility of routine use of brain stem response audiometry in infants is discussed and two cases, which could not be diagnosed other than with the brain stem response audiometry, are reported. In general, the characteristics of the brain stem response are as follows. 1. The response threshold is very close to subjective hearing level. In this study, brain stem response threshold were 10dBSL resubjective hearing level. 2. The Vth wave shows the highest amplitude and has the high reproducibility. 3. Response is not affected by the level of conciousness of the patient. 4. The technique of testing is simple. These characteristics are very convienient for objective audiometry both in adults and infants. However, the source of the brain stem response has not been elucidated as yet and further investigations are necessary.