For the purpose of auditory training in children or infants with nerve deafness, it is very important to use the hearing aids as earlier as possible, and then also essential to find out the real ability of hearing. However, it is relatively difficult to get the hearing threshold of the impaired children or infants, because the results of response do not necessary mean the real sensitivity. These children were observed for a long period, and their threshold were discussed from many viewpoints, for example, the types or grades of hearing level and frequencies (0.5kHz, 1kHz, 2kHz and 4kHz). The results were as follows. The threshold of hearing was tended to decrease until the children grew up to 8 to 10 years old, particularly in 0.5kHz. This decreasing tendency was observed up to the age of 8 to 9 years at 1, 2 and 4kHz, and about 12 years old at 0.5kHz. Therefore, the reliable threshold of hearing in children should be determined after twelve years of age. In addition, the increasing tendency of the hearing threshold was observed not only in high frequency response (4kHz), but also in middle ones (1kHz and 2kHz).
In standardizing acoustic stimuli of electrocochleography and brainstem response audiometry, a realistic method for measuring transient tone stimuli as tone pips or clicks should be established as often pointed out. In this study, the frequency-specificity of the acoustic stimuli was evaluated by means of a real-time digital frequency analyser with the KEMAR manikin constructed as an ear simulator for hearing aid and related acoustic research. In addition, the effect of the frequency-specific tone pips on auditory brainstem responses was studied. The application of the KEMAR manikin could reproduce and simulate conditons of realistic stimulation in electric response audiometry. In particular, tone pips with a rise and fall time of 3 cycles seemed favorable both for the frequency specificity of the acoustic stimuli and for the neurophysiological synchronization.
Human vestibular membranes of the cochlea were studied by light microscopy using the surface preparation technique. The mesothelial cells were large, flat and elongated and they were arranged in a radial fashion slightly bent toward the apex of the cochlea. The form and the arrangement of the epithelial cells became more irregular with aging. Epithelial clusters or epithelial bands were often observed in the membranes of adults. Blood vessels were occasionally found on the mesothelium of the vestibular membrane near the apex of the cochlea.
The influence of the anesthetics (secobarbital, pentobarbital and α-chloralose) on the auditory middle latency response (MLR) was studied in adult cats. The results were as follows: 1) These three anesthetics caused great variations in both the peak latency and the amplitude of Pa component. 2) The early components of M. L. R. were comparatively stable, while the late components of M. L. R. were greatly influenced by these anesthetics. 3) The generator of Na component seems not to be the same as that of Pa component. 4) Special attention should be paid to the anesthetic condition in the discussion on the late component of M. L. R.
Slow vertex responses evoked by pure tone acoustic stimuli were recorded in 4 young adults with normal hearing acuities under natural sleep. The acoustic stimuli of pure tone were given by 20dB above their thresholds. All trials in one person were carried out every 5 minutes constantly, and background EEG was monitered and the stages of sleep were determined according to the criteria of Dement & Kleitman. The sleep was induced naturally without any medication in all examinations. The results were as follows; 1) The most clear and fine waves of averaged responses with the largest N1-P2 amplitudes and the shortest N1-N2 intervals were recorded in awake conditions. The morphology of averaged waves became more unclear as the stage of sleep getting deeper. 2) The averaged responses recorded during change of sleep stage in one trial showed more obscure morphology: longer N1-N2 intervals and smaller N1-P2 amplitudes. 3) In the pure tone stimuli just above the hearing threshold, P2-N2 amplitudes decreased with deepening of the sleep stage. 4) In the examinations with acoustic stimuli, it was difficult to keep the sleep stage 4 constant even in one trial, and this might be caused by the acoustic stimuli.
Auditory brainstem response (ABR) has been applied as one of the neurological examinations in patient with brainstem lesions. Clinically, ABR was recorded ipsilaterally to the stimulated ear. However, clicks applied to one ear possibly stimulate the opposit ear and make responses different. In order to discriminate the localization of lesion, it must be done to clarify wether the recorded ABR is the response to binaural or monaural stimulation in a strict sense. Simultaneous bilateral recordings of ABR in cats have been performed using binaural and monaural stimulation. In the case of binaural stimulation, click were delivered to bilateral normal ears and then to one ear after destruction of the opposite ear. In the case of monaural stimulation, clicks were delivered to one ear before and after destruction of the opposite ear. The results were as follows: 1) Bilaterally recorded ABRs in binaural stimulation consisted of waves 1, 2, 3, 4, and 5, and they had the same latencies and amplitudes between them. 2) In the condition of monaural stimulation, difference in latencies and amplitudes were observed between the response ipsilateral and contralateral to the destructed ear: that is, a) Latency of waves 1 and 2 prolonged (contralateral). b) Reductions in amplitude of waves 1 and 2 (contralateral). c) Enlargement in amplitude of waves 3, 4, and 5 (contralateral). 3) Waves 1 and 2 seem to be the potentials of ipsilateral cochlear nerve and cochlear nucleus, and waves 3, 4 and 5 to be the contralateral brainstem evoked potentials.