Acoustic reflex latency was measured in 14 ears of 7 normal-hearing individuals while pressure in the external ear canal was varied between ±50mmH2O. When acoustic reflex was measured as changes in compliance, a rise preceded a drop at the reflex onset, the biphasic acustic reflex, was observed. Latency “L1” was measured from the stimulus onset until the beginning of compliance change. Latency “L2” was measured from the stimulus onset until the top of the initial rise in compliance. The amplitude ratio of the initial rise to the subsequent drop in compliance was also measured in each case. This amplitude ratio increased in 8 ears and decreased in one ear when the ear canal pressure was raised. When this amplitude ratio increased with the variation of the ear canal pressure, measured latency “L2” elongated. Latency “L1” did not change when the ear canal pressure was varied between ±50mmH2O.
The purpose of this paper is to search for the cause of tinnitus due to the stapedial muscle contraction. Through the observation and experiments three main facts were found as follows: 1) The stapedial muscle contraction usually does not produce tinnitus and occurence rate of the tinnitus is very low. 2) The tinnitus due to the stapedial muscle contraction which is brought about by electrical stimulation of the external auditory canal is objectively audible. 3) The contraction of the intra-tympanic muscles may not make any electrical change in the cochlea. In view of these facts, we concluded that only in rare cases, the stapedial muscle contraction makes the oscillation around the stapedial area and this oscillation makes the noise which is received as the stapedial tinnitus.
The authors studied on the development of the ear, especially of the middle ear, in ddN and CF strain mice histologically. Materials included 54 normal mouse fetuses ranging from 7 to 18 of gestation. Their heads were serially sectioned and stained with hematoxyline and eosin. Results were as follows. The otic vesicle appeared on the day 9 of gestation and then the ear began to develop. Primordia of the 3 ossicles and the otic capsule appeared on the day 12. The facial nerve ran transversely close to the vestibular portion in the region of the otic capsule. Stapedial primordium was observed as a mass of mesenchymal cells laterally to the primordium of the otic capsule, attached to the medial part of the facial nerve. On the day 13, the stapedial primordium still continued to develop with Reichert's cartilage. On the day 14, the malleus and incur were not differentiated histologically. On the day 15, the 3 ossicles were mostly completed in shape and the stapedial footplate seemed to have a bilaminar structure at this stage.
Xylocaine (Lidocaine hydrochloride) was intravenously injected into guinea pigs. Auditory evoked brain stem response (ABR), whole nerve action potential (AP) and cochlear microphonics (CM) were recorded before and after injection. Administration of xylocaine (20mg/kg) influenced on ABR and AP, but had no observable effect on CM. Latency of ABR wave III was prolonged, and a temporary increase of AP amplitude was followed by decrease. Changes in AP were more pronounced in 4kHz tone burst AP than in click-evoked AP. When xylocaine in a dosage of 30mg/kg was given, complete disappearance of ABR and AP, followed by recovery was observed. CM did not completely disappear, and in fact it sustained only about a 75% decay in its amplitude. From the above results, it is concluded that intravenous injection of xylocain affect significantly on ABR and AP than CM. Xylocaine (1mg/kg) was also intravenously given to 10 patients with tinnitus. All 10 patients experienced reduction of tinnitus after injection. However, change in ABR and AP was minimum, showing a slight prolongation of ABR wave latency only in one case.
The authors surveyed the literature and found 20 patients in 11 families of Pendred's symdrome reported in Japan. The diagnosis of this syndrome was made according to the following three criteria, 1. Congenital Sensori-neural deafness 2. Goitre (Almost euthyroid) 3. Positive KCIO4 (or KSCN) discharge test The results were as foolows: (1) Coefficient of consanguinity of the patients was 0.545±0.150 (2) The result of χ2-test (0.8533) indicated no difference on sex-radio between the male patients and the female. (3) Using the proband method of Weinberg, the segregation ratio was calculated as 0.2895±0.0736. (4) The frequency of the abnormal genes is estimated as 0.0008-0.0052 and the frequency of case in general population is estimated as 1.07×10-6-4.59×10-5. Consequently, the authors assumed that Pendred's syndrome is inherited as the autosomal ressesive type.
The influence of the sleep stage upon the morphology and the response threshold of the acoustically evoked 40Hz ERP (Event Related Potential) was studied. The results were as follows: (1) The amplitude of the 40Hz ERP was most prominent when the subjects were awake, and during their sleep state, the amplitude of the response dicreased as they fall into the deep stage. (2) The response threshold of the 40Hz ERP in the awake state was 10±5.5dB and in the sleep stage, 24±4.6dB. These facts suggested that the threshold discrepancy was approximately 13dB and it seemed quite stable among subjects. (3) These data drow our attention to apply the 40Hz ERP for screening test of hearing evaluation.
The authors have developed a new divice for directional hearing test, which totally utilizes an electronic circuit, in place of the former ITD (Interaural Time Difference) generator with two movable microphones in the echoless box. This divice can generate binaural time or intensity differences for various sound sources. Moreover, it is possible to change instantaneously, between the central sound image and the lateral one on the cranium, therefore, just noticeable differences in interaural time are easily measured. With the 500Hz narrow band noise at 30dB SL, the mean interaural time discrimination ability for normally hearing subjects is 41.6μsec, and the rejection limit is 80μsec, but in the case over the age of 60, the mean value and dispersion of values were increased. According to the type of sound sources, the better discrimination orders of localization of sound impression were 500Hz band noise, synthetic vowels, and 500Hz pure tone. A similar tendency was also observed in the case of time versus intensity trade. A comparison of the measurement values obtained with this device was carried out with the results of previous workers, and the clinical applications of this device were discussed. The authors concluded that this device was extremely useful in clinical diagnosis of central deafness.