To observe the effect of severance of the olivo-cochlear bundle, the cochlear round window responses were recorded in guinea pigs after the olivo-cochlear bundle was severed either at the floor of the fourth ventricle or within the vestibular nerve. Section of the COCB at the floor of the fourth ventricle had no remarkable effect on the round window responses whereas section of the vestibular nerve markedly reduced P1. The CM was not influenced by section of the vestibular nerve and no morphological change in the organ of Corti was observed after the nerve section. It was indicated that the lateral olivo-cochlear (LOC) system would play a role in generation of P1, and P1 might represent some inhibitory activity.
A phase spectral analysis developed by Fridman (1982) was applied to detect the amplitude-modulation following response (AMFR), and its clinical usefulness was evaluated. A sinusoidally amplitude-modulated (SAM) tone was delivered to the right ear of 20 normal-hearing subjects. According to Fridman's technique, an ensemble of sweeps was divided into 10 groups to obtain group averages. Then phase variances were calculated using FFT for the group averages. In order to determine the most suitable coditions of the analysis for constructing an automatic detection program using phase spectral analysis, frequency spacing, number of sampling points and number of sweeps averaged for group averages were investigated. The change of phase spectrum as a function of the modulation frequency (20-70Hz) was also investigated. Furthermore, the sensitivity of phase spectral analysis for the detection of AMFR was evaluated. From the results, it was suggested that the most suitable numbers of sampling points and frequency spacing were 512 points and 4.9Hz (observation window was 204.8msec), respectively. Concerning the modulation frequency, 40Hz was the most appropriate frequency for the stimulation from the standpoint of phase spectral analysis. It was also demonstrated that the threshold determination by phase spectral analysis was more sensitive than the detection of the response by waveform configuration.
Speech discrimination scores (SDS) under noisy circumstances were compared between the cases with a middle ear implant (MEI) and a hearing aid of behind ear type (BTE). In 5 patients the tests were performed by using Japanese monosyllabic and disyllabic words list as a test sound and multi-talker noise as a noise source. The intensity of speech sound was 65dB SPL, while that of the noise was varied 65, 70 and 75dB SPL at the position of patients. The SDS were obtained by calculating percentages of correct answers to 50 words with and without noise. When the test using monosyllabic list was performed without noise, the SDSs by MEI and BTE showed no significant difference. However, with noise (65dB SPL) there were significant difference. When the intensity of the noise increased up to 70 or 75dB SPL, the SDSs by both devices depreciated together with significant difference. When the test using disyllabic words list was performed, the results were almost same as those of monosyllabic list. This results indicated that under noisy circum-stances speech recognition by MEI was superior to that by BTE.
Audiometers in Japan have different BC 0dB levels according to the manufacturers' own normal threshold values. As the first step to establish unified reference 0dB, a quastionare was made about the method which the four manufactures in Japan had used to determine their normal BC threshold. And also the equivalent threshold force lelels (ETFLs) of the BC vibrators of the audiometers which were recently calibrated by each manufacture, were measured by means of B & K 4930 artificial mastoid. The result showed that the ETFLs varied form 17dB at 250Hz to 3.5dB at 1kHz and 2kHz, and that differences between the ETFLs and the international BC reference 0dB which was specified in IEC 7566 were appreciable. An early revision of Japanese Industrial Standard (JIS T 1201 Audiometer), which have no effective specification for BC reference 0dB was strongly suggested.
A pure tone masking paradigm was applied to evaluate the contribution of each cochlear partition to the ABR evoked by clicks in 8 normal-hearing and 11 hearing-impaired subjects with cochlear hearing loss. Masker (pure tone) intensity that caused 50% reduction in V-wave amplitude were recorded for several frequencies. Then the maximum masker frequency was determined. 1) The maximum masker frequencies were 3 or 4kHz in eight normal-hearing subjects. 2) The maximum masker frequencies were 1 or 2kHz in six subjects with high-frequency hearing loss. Ninety dBHL of 6kHz masker did not cause 50% amplitude reduction in 5 of these subjects. 3) Sound pressure levels of 1, 1.5 and 2kHz maskers that caused 50% reduction in V-wave amplitude were high in 3 subjects with low-frequency hearing loss. 4) The maximum masker frequencies were 4kHz in two hearing-impaired subjects with flat type audiograms. The results show that the value of the maximum masker frequency is shifting to the direction in which active functions are left among the cochlear partitions. The data of the click evoked ABR refrects the cochlear function of the most sensitive area coverring middle and high frequencies.
The traditional speech level mesuring method by means of the VU meter was evaluated. The standard reference level of speech reception threshold for digit words of 57-S list is determined as 14dB SPL. This paper disclosed the data supporting the specification and discussed the remaining misunderstanding i.e. 7dB SPL which had been inferred from the difference of 1kHz threshold levels between the old JIS and the revised version. The speech level of the newly released digit words list in CD records were measured by the standard VU meter and peak indicating meter. The result indicated that the level of 1kHz calibration tone was bbout 5dB lower than the average of digit words and that this was brought by arbitrary setting of level of calibration tone according to the peak level indicator.
Linearity of evoked otoacoustic emissions (e-OAEs) was investigated in 6 normal ears, by comparing the real tone burst e-OAEs from an ear with the hypothetical tone burst e-OAEs which were calculated from the click e-OAE of the same ear by convolution method. Correlation analysis showed a fairly strong, positive correlation between the real and calculated e-OAEs, and theoretically it indicated the linearity of the e-OAE phenomena in the range of weak stimuli.
The impulse response of the ear was measured in the closed external ear canal by a probe with a sensitive microphone. The spectrum of the impulse response showed a ripple of about 100Hz periods around 1kHz region. The frequency response of the same ear to pure tone stimulations was also measured and it was shown to have fluctuations of almost the same frequency structure as the ripple on the spectrum of the impulse response. The coincidence of them was interpreted as coming from the linear nature of the ear at the stimulus level below saturation. The ripple on the spectrum of the impulse response was mathematically proved to correspond to the delayed evoked otoacoustic emission (e-OAE) which showed up with a latency of about 10msec. It was also proved that the ripple was composed of the frequency components which delayed by 2π in phase every 100Hz frequency increase. It was presumed that the e-OAE was a beat phenomenon which would appear about 10msec after the click stimulation because all the frequency components were in phase after 10msec.
Evoked otoacoustic emission (e-OAE) elicited by click sounds was recorded by two testing apparatus (ILO88: A and laboratory-built e-OAE testing system using probe K-2: B) and parameters in e-OAE recorded by both apparatus were compared. The subjects were 60 ears with type A tympanogram from 30 normal hearing persons. Almost the same distribution of intersubject difference and interaural difference was found in parameters of e-OAE recorded by both apparatus (e-OAE pseudothreshold recorded by apparatus B and total echo power (TEP) and highest peak power (HPP) in e-OAE recorded by apparatus A). There were high negative correlations between intersubject difference of e-OAE pseudothreshold in B and that of TEP and HPP in A. However, the correlation coefficients between interaural difference of TEP and HPP in A and that of e-OAE pseudothreshold in B showed lower values because of the small interaural difference of parameters in both testing apparatus. Based upon these results, we concluded that the parameters such as TEP and HPP in apparatus A could be the clinically useful tool to investigate the function of cochlear micromechanics. Following three criteria for e-OAE present in ILO88 were proposed. (1) Visual detection of e-OAE waveform. (2) Clear cross power spectrum (white part) in FFT pictures. (3) The ‘Repro’ figure is greater than 40%.