When two-tone stimulation with different frequencies (f1<f1) is delivered to the ear canal of guinea pig, a response with mf1-nf2 frequency is generated from the cochlea. This response is called “Distortion Product Otoacoustic Emissions (DPOAEs)”. DPOAEs are not only emitted to the ear canal, but also perceived psychophysically and measured electrophysiologically in the cochlea nerve fibers as a usual tone. However, we still do not know how the DPOAEs are encoded in the auditory system and whether it can be perceived or not in the auditory cortex. Therefore, in this study, the neural responses corresponding to the DPOAEs at 2f1-f2 are investigated in the guinea pig auditory cortex by dye optical recording, which permits the observation of the spatiotemporal neural responses originated from the DPOAEs were observed.
New diagnostic criteria for acute low-tone sensorineural hearing loss (ALHL) were proposed and compared with the conventional criterion (Abe's criterion). Although the selection of criterion should depend on the purpose of its use, the results of the present study suggested that the following new criterion would be appropriate for the routine clinical use. 1) The maximum threshold at each of 125, 250, 500Hz (or 250, 500Hz) is 30dB or more. 2) The threshold at each of 2k, 4kHz is 20dB or less. 3) Unknown eliology, sudden onset, no vertigo. More patients with mild hearing loss are diagnosed as ALHL by this criterion than Abe's criterion. Both ALHL patient groups diagnosed by each criterion showed similar clinical features including good prognosis. Therefore, the new criterion will enable us to investigate the clinical features and pathophysiology of ALHL by the information from ALHL patients including those with mild hearing loss.
We investigated the efficacy of cochlear implantation in the elderly by comparing postoperative speech perception scores and questionnaire results of aged cochlear implant (CI) users with those of younger control CI users. Vowel and consonant perception scores in the aged patient group improved significantly after surgery, and we found no significant difference in the time course of postoperative speech perception improvement and sentence recognition performances between the aged and the control groups. Although subjective evaluation of CI was lower in the aged group under auditory condition alone in noisy circumstances, the overall results indicated that CI is significantly beneficial not only in younger patients but also in aged patients.
The number of electrodes used, the range of frequencies alloted in the electrodes, and the threshold [T] levels of cochlear implant children (4 to 11 years old) with or without cochlear malformations were investigated. Five children with normal cochlear, 3 children with incomplete partitions and 2 children with common cavity deformity were examined. Results indicated that in the incomplete partition's group the T level obtained were higher and the ranges of frequencies alloted into the electrodes were smaller compared to those of the normal group. However, in the children of common cavity deformity, the number of electrodes inserted were much smaller, the T levels were much higher, and the ranges of frequencies alloted into the electrodes were much smaller than those of the incomplete partition and the normal groups. The children with common cavity deformity, therefore, seemed to need other visual stimuli in addition to auditory input through cochlear implants.
Fifty-six patients with cochlear implant 22 (SPEAK, BP+1 mode) operated in Tokyo Medical University Hospital from 1990 to March, 1999, were examined. The relation between the speech perception and T level, C level, and dynamic range was analyzed. The results showed that the values of C level and dynamic range at apical part were higher than that at basal part, and that the lower T level and wider dynamic range contributed to higher speech perception ability.
Optimum speech level is defined by the newly published International Standard of Speech Audiometry ISO8253-3 as the speech level at which maximum speech discrimination score is obtained. In this study, to estimate optimum speech level in cases with sensorineural hearing loss under the standard condition of speech audiometry by the use of 67-S monosyllable list, the results of speech discrimination test obtained from 350 ears of clinical cases were analyzed. They were classified into seven groups according to the degree of hearing loss in 10dB-step. In each group, the number of ears, in which every 5dB supra-threshold level was optimum speech level and non-optimum speech level, were accumulated. And the ratio of ears with optimum speech level against non-optimum speech level was analyzed. Then, we considered that the level at which the ratio was maximum number is most probably the optimum speech level. It was 50dB in sensation level in the group of ears with mean hearing threshold level at the level of 10dB, and decreased about 5dB with every 10dB of the hearing threshold level increased. These results may be useful on choosing test levels in speech audiometry and hearing aid fitting.
Neonatal hearing screening by using automated auditory brainstem response (Automated ABR) was performed in 948 neonates who were 2 to 5 days of age between August in 1998 and July in 1999. One neonate with bilateral ears and four with unilateral ear were referred for further investigation. Two of them were diagnosed as having unilateral profound hearing loss and three were diagnosed unilateral moderate hearing loss. 216 neonates who passed Automated ABR were investigated by the questionnaire about their hearing at 4- and 6-months-old. All of them were not considered to have hearing loss. One false positive ear and no false negative ear were found. Automated ABR was thought to be effective in the neonatal hearing screening. But some problems were also found. The parents who were told that their child might have hearing loss were extremely shocked. They should be supported mentally. The most effective and efficient time when the hearing screening is performed should also be discussed. And it is necessary to do a follow-up survey at hearing screening throughout childhood.
A 24-item self-administered questionnaire that quantifies performance with a hearing aid in everyday life was developed. The profiles assess experience with amplification of speech in three different listening situations (noisy, reverberant, and quiet environments) and in terms of reactions to amplified environmental sounds. Satisfaction was also assessed using the questionnaire. The questionnaire was administered to 82 experienced hearing aid users. Results revealed that 6% of the subjects were satisfied with their hearing aids, 41% were dissatisfied and the remaining 53% intermediate. There were significant differences between the self-assessment performance scores of subjects with different degree of satisfaction. Significant differences were also observed between the self-assessment performance scores for different listening environments. In general, the subjects reported more significant success with their hearing aids in quiet situation and in listening to environmental sounds than in noisy and reverberant situations. Individual differences with respect to amplifications effects, relationship to hearing level, effectiveness and limitation of analog personal hearing aids are discussed.
This investigation is to clarify the morphological effects of chronic electrical stimulation in cochlear spiral ganglion (SG) and cochlear nucleus (CN) of neonatally deafened kittens. Kittens were bilaterally deafened by daily intramuscular injections of neomycin for 2 weeks after birth. Unilateral electrical stimulation was initiated at 9-10.5 weeks of age and continued over a period of 22-47 weeks. Morphometric evaluation of SG cell somata demonstrated 40-70% of normal cell density in the stimulated side, compared with 20-40% of normal in the unstimulated side. The difference, a mean of 22%, in density was statistically significant. However, this stimulation did not produce significant differences in the total CN volume, the CN subdivisions volume and cross-sectional area of large spherical cells (LSC) between stimulated and unstimulated sides. The mean cross-sectional area of LSC was 6% larger in the stimulated side. The morphological effects of stimulation were more remarkable in SG than those in CN. However, comparing with previous studies using the same deafened model, the difference in CN was the best. This result might suggest the characteristics of stimulation in this study, those are early initiation, long-term, higher frequency and/or temporally challenging to the central auditory system was/were useful for surviving cells in auditory pathway.
The auditory brainstem response as a hearing screening procedure was examined on these infants at increased risk of hearing impairment in the neonatal intensive care unit (NICU). The threshold of the fifth wave decreased with increase of age. 0.5% of infants in the NICU had severe hearing loss and needed to use a hearing aid. The background of the 17 profound deaf infants was examined. A hearing screen program was carried out in one of 17 infants because of the high risk. She was diagnosed earlier than the other cases at the age of one month. More than half of infants with sensorineural hearing loss do not have any risk factors and they might have missed hearing loss to be found by programs screening only those infants with risk factors. We concluded that a universal screening program should be accomplished despite of risk factors.