The occurence of thresholdshift due to hearing aid usage is a real possibility, but we should not conclude that hearing aid usage should be discontinued. We should design hearing aid usage from opposite two points of view. One is educational problem, and another is acoustic trauma. As I showed and discussed 5 cases in this paper, threshold of hearing impaired children will easily shift by various causes, for example, conductive components, sudden deafness, virus infection, progressive hearingloss, and acoustic trauma by hearing aid usage. Differential diagnosis of these diseases should be made exactly and carefully by frequent audiological follow up.
Audiometric findings of traumatic deafness caused by explosion were discussed in 18 cases. All subjects complained of tinnitus immediately after exposure to explosion and audiometric examination revealed hearing impairment in 15 cases. About four days after explosion tinnitus faded away in all cases, and after two weeks the hearing impairment was restored in most cases. In order to measure, the difference of sound pressure level in the room, the pistol shot was employed as a sound source. The data obtained in this experiment suggested that individual hearing loss was not always proportioned to the intensity of the sound. As a result, the authors deduced that individual difference of susceptibitily played an important role in the occurrence of the traumatic deafness.
The interaural discrimination test, in which was presented different speech sounds (digits) dichotically, was investigated for the differential diagnosis of retrocochlear deafness. The results of this test in normal subjects and the battery of the test, had been reported in previous papers. The present report concerns the results of the interaural discrimination test performed on 116 patients suspected of having the central disorders. In normal subjects, the discrimination score obtained by each test was close to 100%. On the other hand, abnormal patterns were classified into three types. The normal pattern was called Type I. The cases in which the discrimination score of one ear was normal and that of the other ear was poor were classified as Type II, those in which the discrimination score of both ears decreased and that of one ear was significantly better than the other were classified as Type III, and those in which the discrimination score of both ears decreased similarly were classified as Type IV. The results of the test were compared with clinical signs, comfirmed surgical findings and so on in each case. In regard to Feldmann's suggestion, the authors concluded the following. The pattern of Type II appears to be related to a localized lesion in either hemisphere. In case of the pattern of Type III the lesion can be diffuse. The pattern of Type IV indicates the presence of a localized lesion such as a brain tumor being enlarged and affecting the other hemisphere.
Human fetal evoked response to acoustic stimuli was recorded from the abdominal wall of five mothers at the 32th to 38th week of pregnancy. Tone bursts with frequency of 1000Hz, duration of 50m sec, and rise and decay time of 13msec were given every 4 seconds through a bone vibrator attached to the maternal abdominal wall at then nearest place to the fetal ear. The responses were conducted through an active electrode located on the maternal abdominal wall in the vicinity of the fetal vertex and were averaged by a digital computer. The results were as follows: 1) The typical wave form of the response consisted of four prominent deflections: a negative, a positive, a negative and a positive deflection with respective peak latencies of 100 to 150msec, 200 to 300msec, 500 to 600msec and 700 to 800msec. 2) These deflections of the fetal evoked response were considered to correspond to the four components (N1, P2, N2, P3) of the slow “vertex potential” to auditory stimulus in young children. 3) This fetal evoked response could not be recorded from the abdominal wall of non-pregnant woman or case without tonal stimulation.
The purpose of this paper is to determine the standard use of hearing aids in young children with sensorineural hearing loss. Follow up studies on the audiograms were carried out in 42 children with perceptive hearing loss making use of hearing aids. The results were summarized as follows: 1. About 7 per cent of the subjects showed more than 15dB aggravation in hearing after entrance to the special class for hearing impaired children. 2. There was tendency in those cases that the longer the use of hearing aid, the more the aggravation in hearing. 3. No definite evidence of acoustic trauma due to the use of hearing aid was found in the residual hearing. 4. Adequate guidance and superintendance are essential for hearing impaired children to use hearing aid effectively.
The temporary threshold shifts (TTS) were examined after exposing cats to wide and narrow bands of noise for increasing durations. At the shorter exposure to the narrow band noise, hearing loss was greatest at 4kHz. However, at the longer exposure, there was a progressive high frequency loss. After exposure to broad band noise there was a progressive high frequency loss at all durations. The growth of TTS was almost linear with log exposure time for 1, 2, and 16kHz. However the threshold shift at 4 and 8kHz showed a reversal in growth at 15 minutes exposure for the broad band noise. For the narrow band noise, 16kHz had a very accerelated growth rate and 4 and 8kHz showed agreater growth rate compared with broad band noise exposure. Recovery curves of TTSs were almost linear with log time up to 4 hours after exposure. Then their recovery slope increased. When TTSs at 30 minutes after exposure was less than 10dB, the cats showed complete recovery from TTS within 8 hours, and there was no summating effect on TTS in daily exposure to noise.
The light microscopic structures of the basilar membrane and its adjacent areas of the experimental animal cochlea were studied by the surface preparation technique combined with a silver staining, which demonstrated the following characteristics: 1. The mesothelial cells, which cover the basilar membrane on the side of the scala tympani, are of elongated, spindle-like shape and are arranged in a spiral direction from the base to the apex of the cochlea. 2. Near the apex, however, the mesothelial cells show a radial arrangement running parallel to the fibers of the pars pectinata. 3. The mesothelial cells become narrower toward the base of the cochlea and laterally toward the spiral ligament in the basal turn, lying tightly side by side or overlapping with each other.