Nine children with congenital rubella deafness born in 1987 were examined. Four children were small for date, and three manifested congenital heart diseases, asphyxia and meningo-encephalitis. The ages of diagnosis ranged from 2 months to 2 years. The average thresholds of hearing loss ranged from 78dB to 113dB. Presently 6 cases are in the school for deaf, and 3 cases are in the primary school. Developmental tests, WISC-R tests and K type tests showed PDQ or PIQ scores ranged from 78 to 118 and VDQ or VIQ scores ranged from 20 to 118. It appears highly likely that children with congenital rubella deafness whose birth weights were under 2500g could be associated with neuropsychological development delay or delayed language development for the degree of hearing loss.
Compound action potentials (CAPs) of human auditory nerve evoked by short syllables [a] and [ka] were recorded using extratympanic electrocochleography in 17 ears with sensory hearing loss. Previously, we had examined in 10 ears with normal hearing and reported that periodic CAPs in voiced segment and a prominent CAP at the beginning were observed in both syllables. In 9 out of 17 ears with sensory hearing loss, almost same responses were observed as those with normal hearing while different responses were shown in the rest 8 ears. Particularly, lower CAPs at the beginning than periodic CAPs in voiced segment, which were charasteristic responses with Meniere disease, were shown in 5 out of 8 ears. We concluded that speech stimuli are transformed to different temporal information in the cochlea with inner ear deafness. These results suggested that temporal information of speech is affected by physiological disorders in the cochlea.
Recently, a hearing aid in which gains are so determined that the loudness of input for the hearing impaired subjects at any frequency becomes equal to that for those with normal hearing, have been developed. It is thus needed to estimate a function which describes the relationship between the sound pressure levels of the same loudness for a hearing impaired listener and that for normal hearing listeners. This function is called a loudness compensation function. To estimate the loudness compensation functions correctly for a specific impaired listener, loudness functions of the impaired listener should be correctly measured. Moreover, variability of loudness functions of normal hearing listeners should be taken into consideration, because the normal loudness functions of the hearing impaired listener are absolutely impossible to be known. We propose to give the estimation of the loudness compensation functions not as lines but as bands in which width is calculated by a sum of the intra-subject variance of the loudness functions of the impaired listener and the inter-subject variance of normal listeners. This procedure could give appropriate estimation of the loudness compensation function for hearing impaired listeners with variety of hearing characteristics.
It is dificult to understand a sensitivity and a frequency response of a pick up coil by IEC 118-1 procedure, and to recognize the differences between ‘M’ and ‘T’ position. These problems are caused probably by the inaccurate data of the pick up coil's sensitivity tested at a maximum gain control in the low inductive signal. The author developed an easy and effective test procedure to solve these problems by avoiding many kind of noises. A variable magnetic field test loop system is also assembled for ‘high S/N analizing’. It became possible to us that the accurate and understandable data for analysis, and the usefulness to culculate the out put sound pressure level from a hearing aid used in the loop system. Further, the diferences of hearing aid's frequency responses between ‘M’ and ‘T’ position were shown clearly. The weakpoints of the latest loop systems also became clear in bringing clear sounds for hearing aid users.
A strategic masking method, so-called ABC method, was developed by the first author, and the bone-conduction threshold test was performed with a bone vibrator at the forehead, while the test ear wore a dummy earphone that produced the same occulusion effect as that on the non-sest ear produced by the masking earphone. Because of the occulusion effect yielded by the earphone, the standard reference equvalent threshold force level is not applicable to the bone-conduction test using the ABC method. In order to establish the normal reference level for the method, bone-conduction thresholds were determined using two bone vibrators, Radioear B-72 and Rion BR-41 for 30 young normal adults (30 ears) in the frequency range between 250 and 4000Hz. Equivalent threshold force levels were determined on the artificial mastoid type B & K 4930. The result showed that equivalent threshold force levels for the ABC method were improved by 14, 20, 8dB at the frequencies of 250, 500, 1000Hz respectively, compared to ISO 7566 (forehead coupling) reference levels. These improvements approximately coincided occulusion effects reported for the earphone with MX41/AR cusion.
A study was conducted using 116 subjects with hearing loss through questionnaires for the purpose of datermining how hearing levels, speech discrimination scores, and type of hearing loss affected activities of daily life. Under various conditions, good understanding in communication was more often observed when subjects had better hearing levels and speech discrimination scores, as compared with those having poorer hearing levels and speech discrimination scores. Comparison between types of hearing loss revealed no remarkable differences under most of condition examined. Items affected by all of hearing levels, speech discrimination scores, and the type of hearing loss included meetings with about 5 persons, lecture meetings using a microphone, and sounds in play-houses and movie theaters. These items were considered to be effective questions for the evaluation of the communication disabilities.