The expansion of amplification of digital hearing aid is a new method to increase amplification ratio as imput level increase. The expansion is useful to improve the signal to noise ratio, however, it also changes speech signals. The effects of the expansion on speech discrimination scores were studied in 6 normal subjects by using a digital hearing aid, HD-10. The speech discrimination tests were performed under the signal to noise ratio of 10dB. The speech discrimination scores were not decreased when the expansion ratio of 1:2 was applied to all frequency ranges. When the expansion ratios of 1:4 and 1:8 were applied, however the speech discrimination scores were significantly decreased, compared with those when the expansion was not applied. On the other hand, when the expansion was applied to only low or high frequency ranges the speech discrimination scores were not decreased with every expansion ratio. The expansion is useful to decrease noise without decreasing speech discrimination scores.
This study attempted to investigate within-subject stability of latency of event-related potentials (ERPs) from the stage W to the stage 1. We performed an auditory discrimination paradigm repeatedly more than three times for nine normal adults. During the experiments, the EEG was recorded simultaneously. The latencies of the N1, P2, N2 and P3 components in the averaged wave forms were measured. And we studied the stability of the latencies in the subjects in the stage W and the influence of drowsy (early stage 1) or very light sleep (late stage 1) on the variability of the latencies. As a result, (1) coefficient of variance (CV) of the latencies showed the significant difference between subjects even in the stage W, (2) Between-subject variability of CV of the latencies was more statistically eminent in the subjects in the stage 1 than those in the stage W, (3) in the stage of drowsy, instability of alpha wave during the experiment and synchronization of alpha wave after the target stimuli were considered to influence the averaged wave forms, (4) in the stage of very light sleep, the “sleep and wake” pattern which was triggered by the target stimuli was repeated, and this pattern was thought to be different from the process of attention in the awake stage in the brain.
The speech recognition abilities for vowel, consonant, monosyllable, word and sentence and their progressing were studied in 7 patients with a Nucleus cochlear implant for more than one year. The results obtained were as follows: Vowel perception with audition only (chance level: 20%) was 80% correct (range: 58-100%) in average. Consonant perception with audition only (chance level: 7.1%) was 46% (range: 23-65%) in average, and consonant perception with audition plus vision was 76% (range: 55-86%). Five patients with good results showed a rapid improvement within 6 months after initial use. A patient with the poorest speech recognition out of 7 patients achieved the vowel perception from 30% to 58% correct on after 2 years of use. It was suggested that the patients who have been deaf for a long time showed a slow improvement after the usual use of cochlear implant.
In order to examine the effect of a middle ear lesion on bone conduction response, we try to obtain the normal control data of bone conduction electrocochleograph (BC ECochG). In this study, definite difference of the latency-intensity function and the input-output function between the ipsi-lateral stimulation and the contralateral one were observed. Prolonged latency and decreased amplitude of AP were among the characteristics found in the BC ECochG which was obtained from the contralateral stimulation. These differences between the two stimulations in this study may be explained not only by the interaural attenuation factor of less than 10dB, but also by the conduction time from the contralateral mastoid to the inner ear. Application of this study for ears with conductive hearing loss were also discussed in this report.
A new monosyllable list (TS-1), recorded in a CD disk and consists of 50 nonsense monosyllables was composed. The monosyllables are the same as those of 57 and 57-S lists but the order of the presentation is different from either of these lists. The intensity levels of each monosyllable in TS-1 list is the same as that of the 1000Hz calibration tone. The speech discrimination tests were performed using each of TS-1 list, tape recorded 57-S list and TY-89 list (CD recorded 57-S list) in 8 normally hearing adults. The speech discrimination curves and consonant confusion pattern were compared among the three lists. The results were summarized as follows, 1) The maximum speech discrimination score was obtained at 50dB in all lists. The maximum discrimination score showed no significant difference among the three lists. 2) In comparison of discrimination score at the levels from 0dB to 60dB, the significant difference was obtained at 20dB and 30dB. 3) In comparison of consonant discrimination, low consonant discrimination score at 50dB was “t∫” and “ts” of the TY-89 list. 4) The consonant confusion pattern of the three lists was similar. For the evaluation of the results of speech discrimination tests, we must take account of a peculiarity of each monosyllable list.
Whole blood viscosity and plasma viscosity were measured in 25 patients with sudden deafness (SD) and 70 controls with normal hearing. 1) Whole blood viscosity and plasma viscosity in the SD patients were significantly increased in comparison with those of control group. 2) There was a correlation between the average hearing level of the first pure-tone audiogram and whole blood viscosity in the patients with SD. In patients with low tone hearing impairment, plasma viscosity was found to correlate with the average hearing level. In the patients with high tone hearing impairment, whole blood viscosity was relatively slightly increased. 3) Whole blood viscosity and plasma viscosity in the patients with SD were decreased as their hearing improved during treatment. In some patients with SD, the hearing level was improved in a short period of the treatment. The other patients showed a gradual improvement of the average hearing level in correlation with values of whole blood viscosity and plasma viscosity. 4) There was no relation between the prognosis of hearing and whole blood viscosity and plasma viscosity measured at the first examination. 5) It can be suggested that the increased whole blood viscosity and plasma viscosity might be the significant contributory factors in etiology of SD.
The topographies of the negative components was created by averaged amplitudes in 14 normal adults (n=28), and the result was compared to those of the positive components. The scalp distributions of NIII and NV components were similar to ones of the preceding positive components PIII and PV. However, the distribution of NI component was different from one of PI component and similar to one of PII componest. NII component was occipital dominant similarly to PII component. However, high amplitude side depending to stimulus of NII component was opposite to one of PII. These results suggested that generators of negative components in ABR are not always same with ones of the preceding positive components.
Extra-cellar single unit responses were obtained from the anterior field in the left auditory cortex of the anesthetized guinea pig. After determing neuron's characteristic frequency (CF), neuron was stimulated with CF tone burst given to the right ear of the animal. Neuron's peak response latencies were studied along the whole iso-frequency band from ventral to dorsal. The neurons showing the shortest peak latency were located on the ventral side of the iso-frequency band. Peak latencies were elongated as the recording electrode was moved more dorsally or ventrally from that site. The changing stimulus amplitude did not affect this tendency. These results suggest that in the anterior field the neural activity begings ventrally and propagats dorsally.
A comprehensive survey on use of communication methods by hearing-impaired persons in the contemporary Japanese social life was conducted by sending question naire to a groups of congenitally severely hard-of-hearing adults. The answers were received from 1696 persons, or 45% of 3740 to whom the questionnaires were sent. The results were summarized as follows. 1. Different communication methods were used according to the capabilities of persons to communicate. 2. Handwriting was frequently used when the fast communication was required. 3. Estimated usefulness of those communication methods was highest in the order of signing, fingerspelling, lipreading and hearing aids. 4. Many of the congenitally deaf persons, although they were using mainly signing, looked for the accessibility to communication aids with letters as well as signing.
Electrocochleogram (ECOG) and evoked otoacoustic emission (EOAE) were examined in two patients with intracanal acoustic tumor to elicit the responsible sites of the hearing loss. In the first case, inner ear disorder was suspected by conventional audiometry, and CM threshold and EOAE threshold also strongly suggested the possibility of the retrocochlear lesion as well as the inner ear disorder. The input-output curve of AP showed a steep slope and its threshold was remarkably elevated. These findings indicate that the lesion exists not only in the inner ear, but also in the retrocochlear regions. In the second case, fluctuation of hearing was found on conventional audiograms. The hearing was fluctuating, but the change in CM threshold was quite minimal. The CM latency was prolonged at the low intensity stimuli when the hearing level was improved. In contrast to CM, AP amplitude was improved, when the hearing was improve. The best frequency of the left EOAE was 1.6kHz at the initial examination, but it changed into 1kHz at the final examination performed when the hearing was improved. Ferthermore, its threshold in the initial examination changed to the normal range at the final examination. These results indicated that the decreased hearing level of the second case was not only due to hair cell damage but also due to the damage of the spiral ganglion and/or the cochlear nerve. The ECOG and the EOAE were very useful to evaluate the inner ear damage of the small intracanal acountic tumor.