In ERA interchanged sound stimulus method was used. Apparats used was consisting of interchanged stimulus and EEG divided system and four channels computer. Stimulus interchanged system were able to use four sound stimuli and these were presented to the patient one by one interchangably, simultaneously the EEG were divided to each of the four channels in the computer. Using this method and instrumentation, the effect of changes in the psychologic state which might occur during the test, would be sampled evenly in each of the four responses averaged for each of the four different stimuli. Therefore we were able to compare each of the four averaged responses, and this method was applied for estimation of the response threshold and an objective test for the recruitment phenomenon.
The waveform of the auditory brain stem response (BSR) is considerably affected with the different cutoff frequencies of analog filters inserted into the response recording system. On the basis of this deformation of the BSR by filters, the authors concluded that the BSR was decomposed into 2 components of different frequency ranges. One of them was several successive positivenegative deflections within 10 milliseconds after stimulus onset, and the other a single slow positive deflection with a peak latency of 5 to 7 milliseconds. The authors supposed that the latter component coincided with the P0 component of the middle latency response.
Vibration mode of the human skull was studied by means of holographic interferometry. Three dry human skulls were vibrated with generated bone-conduction receiver for several test frequencies within audible range. After assessing resonance frequencies on each skull, holograms of the vibrating skull were recorded and reconstructed in each resonance frequency principally. Vibration of the skull was clearly discernible not only at the vibrated temporal surface but also the opposite side. Noteworthy findings were vibration fringes on the temporal surface observed at the test frequencies of 400Hz and 100Hz, suggesting a possible component of compression bone-conduction at such low frequency ranges.
Interrelationship of loudness sensation among five Japanese vowels was studied with the use of paired comparison method under three conditions. Under the first condition, the five vowels were pronounced with the same subjective loudness and, consequently, with different intensity. Under the second condition, the vowels were pronounced with the intensity as equally each other as possible. Under the third condition, the intensity of the vowels of the first condition was mechanically adjusted to approximately the same level. All vowels were uttered by a normal male subject at a constant pitch. Thirteen listeners listened to the edited tape through a loudspeaker and judged the loudness difference in every pair on five point scales. The results of the listening test showed that the order of loudness sensation among the five vowels under the first condition was identical to intensity order, i.e., /A/, /O/, /E/, /U/, /I/, and /A/ was the strongest. Under the second and the third conditions, on the other hand, the order of loudness sensation was different from intensity order, and /I/ was judged as loudest while /A/ was judged as softest under both conditions. The results suggest that loudness sensation of vowels is not only related to vowel intensity, but also to some other unknown acoustic factors.
School screening program was administered to the children under school-age. The subjects were 580 children aged from three to five, and 288 school-age children in the first and fourth grades were examined as control. The 20dB (JIS-1956) screening levels at 1, 000Hz and 4, 000Hz were used. Those who failed the first test were retested by the same procedure, and those failed the second test were tested with standard audiometry. The hearing-impaired children were examined medically by an ENT docter. The following results were obtained. 1. Incidences, types and degrees of hearing-impairment and ENT findings in the hearing impaired children under school-age were similar to those found in school children. 2. The percentages of normal hearing children who failed the screening tests were larger than those in the control group, and approximately one third of the children failed the second test were found to have normal hearing. 3. The test time for screening of each child was longer than those in the control group, and in three-year-old children the test time was twice as long as that in the first-grade children. It was concluded from these results that school screening audiometry could be applicable for the children under school-age, though exercises how they response to test sounds before actual screening tests and the tests should be repeated more than three times.
BSR audiometry was applied to 63 ears with hearing losses and 28 normal ears. The auditory stimulus to elicit the BSR was one cycle of a 3kHz sinusoidal wave. Click intensities were calibrated relatedly to the subjective click threshold of normal adults listeners (0dBHL). (1) The averaged BSR-threshold of the normal hearing group was 13.7dBHL. (2) BSR-thresholds in cases with flat hearing losses were close to the averaged pure tone thresholds (averaged from 250Hz to 8kHz). (3) BSR-thresholds in cases of high tone losses had a close correlation with pure tone thresholds at 2kHz. (4) BSR-threshold could predict the pure tone threshold at 2kHz (with the exception of abrupt high tone losses above 2kHz). (5) In cases of abrupt high tone losses BSR-thresholds were considerably higher than the subjective sound thresholds to the clicks.
Two kinds of auditory responses in the guinea pig were simultaneously recorded to study their relations, i.e., the auditory brain stem response (BSR) and the cochlear responses (CM and AP) to click stimuli. The components of BSR, CM, and AP were compared as to their latencies and input-output relations as a function of stimulus intensity. The initial deflection of BSR was identified as CM from their close correlation. The basal turn of the cochlea most likely contributes to CM of BSR. This wave was followed by four distinctive neural components labeled P1, P2, P3 and P4 within 5 msec after stimulation The peak latencies of P1 and P2 did not coincide with those of N1 and N2 components of AP. The start of N1, however, coincided with that of P1 When the stimulus increased in strength, latencies of P1 and P2 were shortened in parallel to those of N1 and N2. As propagating along the auditory nerve, the components of AP would contribute respectively to P1 and P2. The peak latencies of P3 and P4 were 2.0 to 2.5 msec and 3.0 to 3.5 msec, respectively. These value were shorter than those in the cat.
Using various non-occluding earmolds, studies were undertaken to determine the actual gain and coupler gain, and the observations were made for the following points: 1) effects of sound conducting tube, 2) effects of vented earmold, 3) effects of the position of the sound conducting tube in the external auditory canal, and 4) actual gain when hearing aids with open canal earmold were used. The results obtained are as follows. Non-occluding earmold produced a high-pass filter effect. However, the use of a certain vented earmold resulted in an increase of gain compared to the use of occluding earmold at a frequency region between 300 and 700Hz. In the earmold with a vent hole came across the sound conducting tube gain reduced not only in the low frequency region but also in the high frequency region, depending on the site of the vent hole. When an open canal earmold was applied either in model ear or real ear, the sound pressure on tympanic membrane changed in accordance with the site of opening of tube. The open canal earmold had a high-pass filter effect in the high frequency region above 1500Hz, whereas in the low frequency region below 1500Hz, the sound pressure elevated as the opening of the sound conducting tube entered deeper into the external auditory canal, but there was no difference of this effect between model ear and real ear. Actual gain produced by a non-occluding earmold with hearing aids reached its maximum of about 20dB at 3000Hz under the conditions of CROS (Contralateral routing of signals) and FROS (Front routing of signals). However, under the conditions of IROS (Ipsilateral routing of signals), the maximum gain attained was only 10dB at 3000Hz.
The study was carried out in patients with gradual slope sensorineural hearing losses and those with conduction losses. The application of hearing aids was evaluated by performing speech discrimination test using both distorted speech and non-distorted speech, assessment of confusion matrix and a test for the easiness of hearing speech under different noise levels. The results obtained from the present study demonstrated that in the test for application of hearing aids, there were a few patients who showed a slight improvement in discrimination when tested with distorted speech, while a remarkable improvement was seen in discrimination when tested with non-distorted speech, and that in the test for easiness of hearing speech, difference was observed between the scores in quiet and those in noise when using hearing aids either with open canal earmold or with occluding earmold. From the above, it may be concluded that in order to perform adequate application test for hearing aids a test with distorted speech must be carried out in addition to that with standard speech. Moreover, it seems necessary to develop hearing aids in which frequency response can be altered according to the environmental noise levels