The fitting problems of bone-conduction hearing aids for three persons were discussed. They had mixed hearing loss and were using their hearing aids effectively for more than one year. Bone-conduction threshold was ranged between 5 and 40dB at 0.5-2kHz. Their speech intelligibility with bone-conduction hearing aids ranged between 46 and 52% for syllables and between 37 and 90% for words. The main reason for using bone-conduction hearing aids was not for improvement of the intelligibility of speech, but an aesthetical purpose and the inutility of closing the ear hole with an ear mold. The clients were requesting a better fitness of the vibrator and also a lower price for an aid. In the future, the use of these hearing aids in noisy surroundings and decrease of fatigue must be studied on the more scientific basis.

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The reflex activating sounds consisted of a 1000Hz pure tone, and thirteen kinds of noise centered 1000Hz with bandwidth of 100, 250 and 1/3-octave frequencies in 500-5000Hz. The hockey stick regression method which is one of the two-phase regression analyses was used to estimate a critical bandwidth.
The existance of the critical bandwidth was confirmed in 81 subjects out of 89 with normal hearing acuity. The mean value and SD were 30.6±2.2dB (1148Hz).
The present method developed by the authors is one of the useful tools to estimate the critical bandwidth for AR, and the relation between the critical bandwidth for AR and that observed in psychophysical studies such as loudness summation or masking was discussed.

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The histopathological study was carried out to clarify damage in the vestibular organs and cochlea in 93 guinea pigs receiving various aminoglycoside antibiotics (AGs); micronomicin (MCR), kanamycin (KM), dibekacin (DKB) and amikacin (AMK). Pinna reflex test in a wide frequency range from 20k to 500Hz was performed before, during and after the administration of AGs. Any vestibular function test was not done but histopathological investigation of the inner ear was carried out on the serial celloidin and celloidin-paraffin sections of the bilateral temporal bones. The following results were obtained.
1) The hair cell loss always occurred earlier in the vestibular organs than in the spiral organ. 2) The hair cell loss was scattered in mild vestibular lesion but extensive in the severe lesion. 3) The hair cell loss was first seen in the utricular and/or saccular maculae and later in the ampullar crests of the semicircular canals. 4) The hair cell loss occurred in some of regions in mild vestibular lesion, but in all of them in the severe lesion. 5) The bilateral occurrence of the hair cell loss in the individual regions was noticed to the same extent in more than 80%. 6) Lower dose (50, 25, 15, 10mg/kg) of the aminoglycosides, either KM, DKB and AMK with relatively high ototoxicity or MCR with low ototoxicity induced very limited loss of the outer hair cells mostly at the basal end of cochlea in low incidence (less than 20%). In the vestibular organs, hair cell loss was scattered, but occurred in almost 100% of the animals given the above mentioned drugs. 7) At high dose (100, 150, 400mg/kg), there was distinguished difference in incidence and extent of the outer hair cell loss between the aminoglycosides with high ototoxicity and MCR. KM and DKB caused extensive loss of the outer hair cells in high frequency (83, 100%), but MCR induced limited loss of the outer hair cells in low incidence. In the vestibular organ, the hair cell loss was extensive 100% in the animals treated with KM and DKB, but 100% in less extensive area in the animals treated with MCR. 8) These results may contribute to understand the affinity of the aminoglycosides for the vestibular and spial organs.

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The auditory post-auricular responses (PAR) were recorded in 28 children aged 0 to 12 with unilateral microtia, and the influence of the post-auricular muscle (PAM) development on the responses were investigated. Responses obtained from the sides of microtic ears and normal ears showed no significant differences in the wave form, threshold, latency, nor in amplitude. Muscle volume of the PAM did not affect the amplitude of the PAR.

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Our previous experimental study indicated that the ABR consisted of, at least, fast components and slow positive component. Furthermore, it was revealed that the inferior colliculus (IC) had a close relation to the slow component of the ABR, and acoustic stimuli evoked a large negative potential in the IC and electrically positive field surrounding the negative potential.
In order to reveal the electrical relation between the evoked potential of the IC and the slow positive wave of the ABR, electrical stimulation was applied to the lateroventral part of the IC where nerve fibers penetrate into the IC. Thus, the evoked potentials in the IC and the ABR were recorded.
The evoked potential of the IC was large negative wave and the ABR was slow positive wave, when the electrical stimuli were applied. These waves look like ones evoked by acoustic stimuli.
As result, the large negative potential of the IC plays important role to form the slow positive wave of the ABR, however, it might not be essential for generation of the several sequential fast waves of the ABR.

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Power spectral analysis and investigation using digital filtration on the auditory middle response (AMR) to tone pip of 1000Hz were performed. The subjects were 13 children aged 1 to 4 years, 13 children aged 5 to 7 years and 9 adults. All of them were proved to have normal hearing.
The dominant: power of Pa ranged in frequency 20-50Hz in adults, and about 20Hz in children. The detectability of Pa was 90-100% by the digital filtering between 20Hz high pass and 50Hz high pass in adults. It was particularly high in 20Hz high pass in children (75% in the group of younger children and 92.3% in the other group) and sharply decreased at 30Hz high pass. The peak Pa and Nb showed a significant increase in latency in children compared with that in adults. The peak Pb was frequently found at 30Hz high pass in adults, but it was hardly detectable by any high pass filtering in children.

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