The standard method of evaluation for tinnitus, determined in Japan Audiological Society in 1984, recommends 5dB step measurement in loudness of tinnitus. But the standard method is insufficient in accuracy for clinical examination. Therefore loudness matching of tinnitus with a constant method using microcomputer-based device was developed. Tones, as substitute for tinnitus, were presented through bone conduction to subject without impaired hearing and loudness of the tone was measured with the constant method and the standard method. In the constant method, a minimum audible level was also measured with the same way. The values of loudness level were indicated sensational level. The number of subjects was 29 and their ages ranged from 24 to 43. Reliability of each method was evaluated. The result showed that the constant method was statistically more reliable than the standard method. Only in cases with the constant method, 2dB variation of loudness of probe tones could be detected sufficiently. In the constant method, parameter respected to play an important part in evaluation for reliability of loudness matching could be caught simultaneously. Furthermore, as it took 20 to 40 minutes for the constant method, our method seemed to be sufficient for clinical use.
The relationship between hearing threshold level and speech discrimination score was studied in 806 cases of bilateral sensori-neural hearingloss. The correlation coefficient between hearing threshold and speech discrimination score in the subjects was 0.719. The difference of hearing threshold level between each ear in a subject and difference of speech discrimination score were distinct, and it was 0.833. The 10% decrease in speech discrimimation score corresponded to a 10dB increase in hearing threshold level. Based on the latter correlation, the 80% reliability range for the estimation of the hearing threshold level was 15dB. When the speech discrimination scores of both ears were compared for a subject, the degree of difference in inner ear impairment could be assessed by decreasing the influence from the central auditory pathway, which varied between subjects.
The relationship between speech discrimination score, degree of hearing loss, age, and use of hearing aid were studied in 329 cases of a sensorineural hearing loss. Speech discrimination scores in these patients were distributed widely, and the differences in the scores were large even among those with similar hearing threshold levels. Therefore, to assess hearing loss, speech discrimination tests are an indispensable in addition to pure tone audiometry. Speech discrimination scores decreased remarkably in those in the 8th decade, compared with younger patients. Presbycusis due to retrocochlear disturbance was prevalent in patients in the 8th decade. The use of hearing aids in patients of advanced age was slightly less frequent in those with a mild hearing loss and good discrimination. However, the rates were still 75 percent.
A new modified measurment in the bone-conduction test using bone conductive noise which had been originated by Rainviile in 1955 was devised. The differences between the original method and the new one are follows: 1. Critical narrow band noise is used instead of original white noise. 2. For hearing of air conductive tones, an insert earphone is used instead of a supraaural earphone in the original method. 3. The level of air conductive tone which is interrupted by the bone conductive noise is a higher threshold level than threshold level in the original. Because of the modification above, the new method was found to make bone-conduction test simpler than original one. For using this new modified method as an ordinary clinical test, three basic experiments were carried out and some points were found to be investigated.
In this study, two clinical experiments were conducted. The first one is the experiment comparing the results of the plateau measurement, which is broadly used, with the results of the new modified Rainville method. The subjects consisted of 10 normal adults, 10 adults with a conductive hearing-impairment, and 10 adults with a sensorineural hearing-impairment. The other is a trial of the new modified Rainville method on a hearing-impaired adult whose bone-conductive thresholds was not estimated by the plateau measurement. In the first experiment the difference between both measurements was slight, and in the second one the thresholds of the subject were measured by the new modified Rainville method. In addition, the procedure of this new modified method was found to be easier than the original one, the other modified tests and the ordinarily used plateau measurement.
A questionnaire was sent out by mail to 524 subjects, and 243 replies or 46.4% were submitted to the survey. The results obtained were as follows: 1) Only 134 (55.1%) subjects received fitting for their hearing aids and they were explained of its function and limitation. 2) Although hearing aids were used by 189 (77.8%) subjects, only 156 (64.2%) used it effectively. These results were inferior to other surveys. Inappropriate fitting and explanation of hearing aid were thought to be major causes of the inferiority. 3) Some significant relations between effectiveness, frequency of use, complaints about their hearing aid, and other factors were found. Then it was suggested that the effectiveness and frequency of use of hearing aid can be improved by regarding these results. 4) Further study should be performed to clarify the detailed content of fitting services for hearing aid users in Hokkaido, and the methods of resolving user's complaints about their hearing aid.
Wave IV and V of ABR are not always easily identified, because of their modality of a compound formation of IV-V Complex. To investigate this TV-V Complex of ASR the influence of the slow component of ABR was studied. If the slow component is removed by filtering, the TV-V complex is separated into wave IV and V to some extent. However if the filter pass band is narrow enough, this complexed wave is separated with no exception because of artifact. Computerized simulation suggested that the separation of the IV-V Complex is partly due to the filtering.
Axonal regeneration is observed in the commissure of the inferior colliculus (CIC) of mice following its transection. We examined whether the regenerated CIC axons could re-establish synapses with neurons in the inferior colliculus (IC), using the electrophysiological method. The CIC transection of the mice was made at the age of 4 weeks and they were used for the experiment at least 4 weeks later. In the intact control animals, the electrical stimulus presented to unilateral IC made some effects on the acoustic responses of the neurons in the contralateral IC. 65% of the IC neurons responsive to the acoustic stimulus were inhibited by the electrical stimulus, and 10% of the neurons showed summational or facilitative responses to the combination stimulus. 25% of the neurons were undefined for their response properties to the electrical stimulation. In the operated transected animals, 53% of the IC neurons responsive to the acoustic stimulus were inhibited by the electrical stimulus, and 9% of the neurons showed summational or facilitative responses to the combination stimulus. 38% of the neurons were undefined. With respect to the response patterns, many neurons in the animals operated upon were similar to those in the control animals. These results suggested that the regenerated CIC axon re-established synaps with neurons in the IC and that newly established neural circuits were similar to those in the intact animals.
Emission cochleogram was investigated in 17 cases of unilateral cochlear hearing loss consisting of 5 cases of unilateral deafness, 8 cases of sudden deafness and 4 cases of Meniere's disease. The stimulus sounds were tone-bursts at 5 frequencies between 1kHz and 4kHz. The results obtained were as follows: 1) The pseudothreshold of evoked otoacoustic emission (e-OAE) was elevated in all affected ears. 2) The configuration of emission cochleogram corresponded well with that of the pure tone audiogram in each affected ear, considering the fact that the pseudothreshold is elevated at high frequencies even in normal hearing ears. 3) The sum or mean value of interaural differences of pseudothresholds at several stimulus frequencies between 1kHz and 4kHz could be a more excellent clinical indicator than the interaural difference of pseudothreshold at a single stimulus frequency in order to predict the function of cochlear micromechanics more precisely.