Since the first edition was published in 1956, the Japanese Industrial Standard for audiometers, JIS T 1201, has been revised 4 times. In the first two revisions in 1963 and 1976, each of the original two types of audiometer was graded into two sub-types, and the items requiring compliance increased. The SI unit was also introduced. The reference sound pressure levels of the earphone were revised in accordance with ISO 389 in the third revision in 1982. In the 4th revision in 2000, the JIS conformed with IEC 60645, in which audiometers were classified into 5 types, and the reference levels of bone vibrator output and masking noise were specified. The specification of the speech audiometer was newly published as Part 2. The next revised edition will be published in the near future, where the reference levels of insert earphone, circumaural earphone and sound field measurement will also be specified. Even in the audiometers conforming to the latest standard, there remains a problem in that the mean normal hearing threshold levels at low frequencies do not coincide with 0 dB, but are raised by about 5 or 10 dB. Another problem is that there are some discrepancies between the JIS and corresponding IEC standard.
The authors followed the development course of a language and the cognitive neuropsychological ability in two children with progressive nerve deafness wearing cochlear implants (CI), one having worn a CI since 3 years and 6 months old, and the other having worn a CI since 6 years and 11 months old. We obtained the following findings: 1) Wearing the CI proved effective as far as the subjects' language ability and neuropsychological cognition were concerned; 2) when the two subjects with progressive nerve deafness wore their artificial cochlear implant and underwent a systematic training program for a certain period of time before and after entrance to elementary school, they demonstrated many age-appropriate abilities by the age of 9 years and 5 months; and 3) the speech therapist must identify the problem in children as soon as possible, so that verbal learning conditions can be fixed. An appropriate prognosis can be arrived at, and the required appropriate training can be applied. The check list previously suggested by Mori proved effective to arrive at a prognostic value.
Measurements of real-ear insertion gain (REIG) and functional gain (FG) in 5 frequencies from 250 Hz to 4 kHz were compared for the same subject and using the same hearing aid in 80 subjects during the process of fitting a hearing aid. For non-linear hearing aids, REIG for the same input level as the aided threshold in FG measurement was used for comparison. In only 1 subject with a CIC hearing aid, REIG could not be measured because of the feedback. For the other subjects and at frequencies from 250 Hz to 2 kHz, the two measures showed a relatively good agreement to the extent that their averages coincided with each other within 1 dB, and standard deviations (SDs) of their difference were 5 to 6 dB. At 4 kHz, however, REIG lowered FG by about 5 dB on average, and the SD of their difference was larger than at the other frequencies. These tendencies appeared to be caused by some technical factors including the dislocation of the probe tube when inserting the hearing aid during REIG measurement. Although FG measurement is inevitable in some special circumstances, REIG was confirmed to have more advantages than FG for evaluating hearing aid gain under normal circumstances.
Distortion product otoacoustic emission (DPOAE) has been revealed to be periodically suppressed with an additional low tone stimulus. It has been suggested that this phenomenon could be used to detect endolymphatic hydrops. The aim of the present study was to verify that this phenomenon could be consistently detected in normal hearing subjects. Intra-canal sounds were measured with two stimulus tones for DPOAE measurement (3278Hz/70dBSPL and 3999Hz/60dBSPL), and then with these together with a low tone (47.68Hz/100dBSPL). A short time Fourier transform was applied to the sound data, the time course of the 2f1-f2 element was estimated and compared with the phase of the low tone. Seven adult subjects with normal hearing participated in the study. The right and left ears were measured twice. In 4 subjects the width of fluctuation with the low tone was more than the double the width without the low tone stimulus in all of 4 sessions, under the condition that the width without the low tone was less than 0.5dB. In three of these subjects, the phases of the peaks and the troughs of the waveforms of the two sessions in the same ear were nearly equal. The average phase of the troughs in these 3 subjects was 65 degrees delayed from the phase of the peak to rarefaction of the low tone.