The Metz-test is based on elicitation of the bilateral stapedius reflex. The stapedial reflex is elicited by acoustic stimulation in the ear to be examined and measured by impedancce meter in the contralateral ear. In the normal ear, the reflex threshold is 50-90 dB above the hearing threshold. In the ear with loudness recruitment, however, the difference between the threshold for hearing and the threshold for induction of the stapedius reflex reduces. In the present study forty-seven patients suffering from neurolabyrinthopathy were subjected to examine recruitment by the following methods: the Metz-test, SISI-test, Békésy audiometry, and with the unilateral hearing loss patients, ABLB-test. Sixteen ears showed the unilateral hearing loss and sixty-two ears bilateral hearing loss. As the result, there was the almost complete agreement among the Metz-test, ABLB-test, SISI-test and Békésy audiometry in the patients showing recruitment. The Metz-test showed the highest degree of validity among all the the tests. Furthermore, the method is objective and does not require the subject's collaboration, and it can be used in the cases of bilateral hearing loss.
Regarding the earphone used in audiometers standardized by JIS or ISO, it was impossible to examine the hearing of high frequency over 8, 000Hz. In this respect “Rudmose” high frequency audiometer was used together with the open-air type condenser earphone and high frequency generator or the amplifier. The hearing of high frequency was examined by “Rudmose” ADF-4 system and the combination of MX-1E with a remodelled old audiometer. The results showed that ADF-4 was unable to suit for precise test of the hearing of high frequency because the structure of the earphone made the continuative frequency test impossible and the tone signal was difficult to hear. The combination of MX-1E and a conventional audiometer was also examined, but concerning the open-air type, the dip near 13, 000Hz couldn't be removed. There, the insert-type condenser earphone which lessened the distance between diaphragm and tympanum was used with the trial high frequency audiometer. It was confirmed that this earphone was practical because the high frequency sound was easily produced, and the output calibration was possible with 0.2cc coupler, and no dip was produced in the high freqency range.
Results of impedance audiometry were analysed in 56 infants complaining of hearing loss or speech retardation. These infants were received other audiological examinations at the same time such as ERA, BSR and Electrocochleography. The results were as follows: 1) In the normal hearing infant, predicted by other objective audiometries, the stapedius reflex threshold to white noise was the lowest. 2) Even in the normal hearing infant, the reflex to 4, 000Hz were often absent. 3) The stapedius reflex was not useful as a diagnostic procedure of hearing threshold determination. 4) The results of static compliance measurements indicated a median of 0.29cu. cm. 5) Most of infants (about 90%) indicated type “A” of tympanogram.
Reference Equivalent Threshold Sound Pressure Levels (RETSPL) for 3 different types of Japanese earphone and TDH-39 earphone were determined at 8 audiometric frequencies. Alternative binaural loudness balancing was accomplished by the subject who matched the variable tone presented through the experimental earphone to one ear to the standard tone presented to the other ear three times at 30dB hearing level re ISO 389 in the WE-705A standard earphone, then the standard experimental earphones were reversed and the variable tone was matched to the standard tone. Based on mean attenuator setting of 8 subjects, RETSPLs in the NBS-9A coupler for experimental earphones were derived using B&K sound measuring system. There were found great differences in RETSPLs between earphones made in Japan and in the United States while small among the Japanese.