The averaged whole-nerve response (AP) was recorded from the round window of the guinea pig. The sound stimulus was the downward shift of the frequency of a pure tone accompanied with the amplitude increase, and it has been proved that this stimulus could elicit the frequecy-specific response. The peak latencies of the APs for 250Hz, 500Hz, 1kHz, 2kHz and 4kHz were studied in various intensities of each tone and it became evident that the latency decreased almost exponentially as the frequency of the stimuli increased at an octave step. The distance from the round window to the newly activated area of the basilar mambrane by the frequency shift could be expressed as an exponential function of the peak latency of AP, and the coefficient of the function was obtained by the use of microcomputor.
For a clinical application of the implantable hearing aid, two kinds of preliminary experiment were performed using a small electromagnetic transducer with a coil and a permanent magnet. The capacitative probe was fabricated to measure the vibration, the output of the transducer, and it was revealed that the frequency characteristic of this system was flat in the range of 0.5 to 3kHz. The animal experiment was performed on the guinea pig. The device was connected to the ossicles and the amplitude of the cochlear microphonics was measured when the sine wave electric current of various frequencies were applied to the device. The relation between the amplitude and the input current voltage was linear. However, the frequency characteristic curves were not flat and a few resonant frequencies were observed and varied according to the conditions of connection of the probe to the ossicles. Further electrotechnological, audiological and immunological studies are necessary before the implantable hearing aid (“artificial middle ear”) is applied in a clinical case.
Effects of high pass filtered masking noise on the amplitude and sign of SP were studied using the E Coch. G technique. SP and AP were recorded from eight subjects with normal hearing by means of the transtympanic electrodes using 2kHz-8kHz tone bursts as acoustic stimuli. The following results were obtained. 1) The effect of masking on the SP amplitude was less significant for the decrease in amplitude than that on the AP amplitude. 2) As the cut-off frequency of high pass filtered masking noise was approximated to the frequency of tone burst stimulus, SP amplitude became remarkably decreased. 3) The change in sign of SP was not observed using the high pass filtered masking noise. It is concluded that the SP recorded by the transtympanic technique in human is specific to the frequency of tone bursts with higher stimulus frequency than 2kHz. Furthermore the SP in man seems to have different characteristici from the AVE-SP in animals.
In 2024 head injury cases, the contingecy tables were made and X2-tests were done in order to investigate the relation between several indices obtained at the time of injury and several variants showing the change in tinnitus. The results were summarized as follows. 1) There was no remarkable corelation between nose bleeding, sanguineous spinal fluid and tinnitus. 2) There was remarkable corelation between abnormal tympanic membrane and tinnitus in the practical sense. 3) There was remarkable corelation between age and tinnitus. 4) The relation between unconsciousness and tinnitus was not predictable.
Band-limiting experiments were performed at noise spectrum level No=20dB SPL for simultaneous and forward masking. The threshold of signal pulses masked by masker bursts as a function of different variables, such as masker bandwidth, signal frequency, signal duration and delay time between onset of masker and onset signal was measured. The results were as follows: 1) The data for simultaneous masking showed that the slope for subcritical bandwidth was significant for its 3dB/oct slope and the slope gradually was transferred to the broad band threshold. The data for higher frequency signal of forward masking, however, were clearly recorded as a shallower slope. 2) The masker bandwidth which was effective in producing forward masking might be narrower than the critical band measured with simultaneous masking for 0.5, 1, 2, and 4kHz signal pulses. In addition the data for simultaneous masking were well described by a level-dependent critical bandwidth upward spread. 3) As the masker bandwidth was increased by ten times of the critical band the threshold (overshoot) increased by about 10dB at onset of masker for simultaneous masking. The data for forward masking, however, threshold (suppression) decreased by approximately 10dB. The overshoot would depend upon changes in the transient response of auditory system, whereas suppression of forward masking would result from decrease in steady state response of the masker.
A 52-year-old woman with Kearns-Shy syndrome was reported in regard to audiometric findings in her clinical course of five years' duration. The patient first noted a hearing loss at the age of 41, and it was slowly progressive. The first hearing test was performed at the age of 47, and a pure tone audiogram showed a moderate sensorineural hearing loss bilaterally, which was formed rather prominent above 1000Hz. At the age of 49, a pure tone audiometry revealed deterioration of bilateral hearing only at 250Hz and 500Hz. For the last three years, her hearing remained unchanged. Speech discrimination was extremely poor. Békésy audiogram showed type II tracing according to the Jerger's classification. The contralateral stapedial reflexes could not be elicited for the pure tone signal (125dB HTL) at 500, 1000, 2000, 4000Hz. Although the lesion of the hearing loss was not determined, the author suggested that the hearing loss of this syndrome might result from cochleosaccular degeneration.
A new apparatus for improving the signal to noise ratio of electrophysiological on-going activities before averaging the auditory brain stem responses (ABR) in man was successfully developed. A new digital artifact rejecter can discriminate good signals in ABR audiometry by means of the computer technique. The usefulness of this apparatus was amply proven in recording ABR in this study, It was a great advantage of this digital method that good waveforms of ABR could be obtained from the electrophysiological data in man by avoiding any deformation of original waveform patterns of ABR.