The purpose of this study is to find appropriate electroacoustic characteristics of hearing aids to fit to the patients with a conductive or mixed hearing loss. In analysis of the clinical records of 100 cases of conductive loss, 144 cases of mixed loss and 477 cases of sensorineural hearing loss, the most suitable maximum output-sound-pressure-level (MOSPL) and the most suitable frequency responses of hearing aids for conductive and mixed hearing losses were studied. In addition, the uncomfortable levels (UCLs) and the most comfortable levels (MCLs) were measured in 25 patients. They consisted of 9 cases of conductive loss, 9 of mixed hearing loss and 7 of sensorineural loss. The results were summarized as follows: (1) In the cases with conductive hearing loss, the averaged optimal MOSPL was about 8dB higher than that of the sensorineural hearing loss at each hearing level. In the cases with mixed hearing loss, it was about 4dB higher than that of sensorineural hearing loss. (2) The most suitable frequency response for conductive and mixed hearing losses was that with a low-frequency cut-off slope 6dB/octave. (3) The UCLs and MCLs in the cases of conductive and mixed hearing losses were almost the same as in sensorineural hearing loss. As a conclusion, for conductive and mixed hearing losses, the hearing aids with a high maximum output level were not necessary. The hearing aids with the sufficiently amplified low frequencies were found appropriate.
Distortion product otoacoustic emissions (DPOAE) and DP-grams were obtained in the guinea pig with kanamycin-treated cochlea. The animals were examined with reference to the histopathology of the outer hair cells (OHC) of the corresponded cochlea. The DP-gram and the histopathological cochleogram basically showed well matching. The result suggested that the generation of DPOAE requires normal OHC, and that DPOAE measurement can be used to monitor the frequency specific integrity of the cochlear damage.
Reaction time and response accuracy under a two-tone discrimination (odd ball) task were measured in nine cochlear implant recipients. The age of the subjects ranged from 17 to 70 and the mean was 53.7 years. Two different pitch tones were offered to the subject in random order. When the stimulus was rare-target, the subject was asked to lift of the thumb finger. Frequent-nontarget tones was 1000Hz, wheres the rare-target tones were 2000Hz, 1500Hz or 1200Hz tone during each block. As the result, the recipients decreased an ability to pitch detection. The avaraged reaction time was 382ms and the response accuracy was 91.7% when the rare tone was 2000Hz. When the frequency of target tone became closer to the frequent tone, the false response and reaction time increased significantly (P<0.05, t-test). There was a great inter-individual difference in the ability of frequency discrimination. The response accuracy showed significant correlation with the score of the speech tracking test (p<0.05). These data suggest that this measure may be useful in assessing their auditory discrimination ability.
Event-related potentials were recorded in seven cochlear implant recipients during a two-tone discrimination (an oddball) task. The aim of this study was to determine the frequency discrimination ability and to investigate central auditory information processing in cochlear implant recipients. The age of the subjects ranged from 54 to 70 years and the mean was 60. Frequent-nontarget stimuli were 1000Hz tone throught the recording blocks. The rare-target stimuli were 2000, 1500 or 1200Hz tone during each block. As the result, the N100 and P300 waves were evoked by an oddball task in all subjects. When the rare-target tone was 2000Hz, the mean amplitude and the latency of N100 was -2.7μV and 121.5ms, respectively, and those of P300 was 15.1μV and 351.3ms, respectively. The amplitude of P300 decreased and the peak latency of P300 was prolonged remarkably when the frequency of rare-target tones became closer to the frequent tone. ERPs recordings on cochlear implant recipients may be useful aid to assess their auditory cognitive function objectively.
It is well known that a frequency response via induction coil of a hearing aid is different from a frequency response via microphone (low tone part is especially reduced). Because of this phenomenon, meny hearing aid users dislike “via inductive coil sound”. Auther developed a hi-definition induction loop system to obtain a frequency response via microphone. Further, an improved telephone and a small sized induction loop system (apprication systems) is tested by hearing aid (equipped with an inductive coil) users (average 80-105dB HL). The results obtained were as follows; 1) A hi-definition loop system was used effectively for all kinds of hearing aid (equipped with an inductive coil) users. 2) It was proved that “via inductive coil sound” became comfortable and clear by using a hi-definition induction loop system. 3) For more comfortable listening, a hi-definition induction loop system with a trimmer in a magnetic field is very effective.
Chronically implanted electrode in the round window using a special adhesive agent (ARONALPHA) was used in 18 healthy guinea pigs in this study. Six animals weighed 250-350g showed a loss of response within 24 hours after surgery. It seemed to be attributed to perforation of the round window membrane which may be vulnerable in small weighed animals. Another 2 animals weighed 250-350g and 4 animals weight 350-450g shoved marked reduction in response amplitude in 2-7 days after the surgery, which might be caused by the shift of an electrode tip from the round window membrane. Four of them developed otitis media additionally. Another 6 animals weighed 350-450g presented the robust CAP with normal threshold and amplitude for a long period of time. This technique was successfully applied in various types of chronic experiments for 4 to 6 weeks. It was said that despite of the some limitations our method is useful to implant a chronic electrode easily in the animals.