Three-dimensional dipole tracing of ABR (wave V) was carried out in normal adults. The current dipole model is usually used as neural electric generators. The ABRs in this study were elicited by the unilateral acoustic stimuli and recorded from 16 electrodes using balanced non-cephalic reference electrodes (BNEs). Active electrodes were placed at 16 sites on the scalp in according with the international 10-20 method. Click stimuli (100dBnHL) were used and a band noise masking (50dBnHL) was applied for contralateral ear. The evoked potentials from the 16 electrodes were amplified using with a band pass filter (20-1500Hz), and they were averaged up to 2048 times. The elecited dipole was presented by both the location and the vectormoment on the head model. In order to estimate the location and the vector moment of the dipole, the inverse dipole solution was applied under the Dipole-Tracing method. The head model was constructed from 17 slices of CT-images of a human skull. In this study, the dipole of wave V moved from the ipsilateral brain stem to the contralateral, and furthermore, upward, forward, and finally downward.
The location and vector of equivalent dipoles of AEP (MLR) sources in 5 normal adults were elucidated electrophigiologically under Dipole Tracing Method. The MLR has been recorded with 70dBnHL clicks bilatelally. The AEP (MLR) sources were analyzed from 0msec to 50.0msec latency under the Dipole Tracing Method. The location of equivalent dipoles were classified into 3 groups. The first group which were analyzed from 0msec to 20.0msec, were located near the brainstem. The second group, from 20.0msec to 40.0msec, were recognized in the posterior lesion of corpus. The third group, after 40.0msec, were found near the location of the first group. The vector of these 3 groups showed no constant direction.
The subjectively estimated pitch of tinnitus was compared with the results of pitch match test using a pure tone audiometer. Also, the relationship between subjective expression by onomatopoeias and the results of pitch match test was analysed. The subjects were 115 tinnitus ears without hearing loss or associated with cochlear deafness. The results obtained were as follows; 1) The pitch of tinnitus was subjectively estimated as ‘high’ in two thirds and as ‘low’ in the remaining one third. 2) When the pitch was subjectively estimated as ‘high’, the measured pitch existed in the high frequency areas beyond 4kHz in 80.0% of the ears. On the other hand, when the pitch of tinnitus was subjectively estimated as ‘low’, the measured pitch was distributed almost equally in all frequency areas and the tinnitus was not simulated by either pure tone or band noise of the pure tone audiometer in 33.3% of the ears. 3) Although the pitch was subjectively estimated as ‘low’ in only one third and as ‘high’ in the remaining two thirds, an almost equal number of onomatopoeias were used for the subjective expression in both groups. 4) The relationship between the onomatopoetic expression and the simulated tones of pure tone audiometer was analysed in 23 onomatopoeias. The tinnitus expressed by 15 onomatopoeias was simulated by pure tone and that expressed by 1 onomatopoeia by band noise. The tinnitus expressed by the remaining 7 onomatopoeias was simulated by both pure tone and band noise. 5) When the tinnitus was expressed by the onomatopoeias simulated only by pure tone, the measured pitch was confined to the frequency range of 1 octave or less, while it was distributed beyond 1 octave in tinnitus expressed by onomatopoeias simulated by both pure tone and band noise. Therefore, the onomatopoeias simulated only by pure tone could be a clinical indicator of the measured pitch, but the onomatopoeias simulated by both pure tone and band noise could not be. 6) As far as the relationship between onomatopoeias and their corresponding frequency areas of pure tone and band noise was concerned, discrepancies were found in 8 (47.1%) of 17 onomatopoeias between the results obtained in this study and the proposals by the standardized tinnitus test in 1984: the measured pitch in this study existed outside the proposed frequency areas in tinnitus expressed by 5 of the 8 onomatopoeias.
CNV audiometry is useful for diagnosis of a psyhcogenic hearing loss, But in malingering whose co-operation is not obtained enough, it is not sure that CNV audiometry can be performed. In this experiment CNV audiometry was carried out in experimental imitation of malingerings of 8 subjects with normal hearing threshold. As a result it way concluded that CNV audiometry was possible and could point out the hearing level near the threshold of audibility even enough in the experimental imitation of malingering. This result was suported by the statistical analysis of mean amplitude of the CNV and response time. The usefulness of CNV audiometry in malingering was suggested.
Onomatopoetic expressions for the test tones presented by pure-tone audiometer were investigated in 3 groups consisted of 37 normal hearing ears without tinnitus, 35 ears of sensorineural hearing loss without tinnitus and 46 ears with tinnitus. The test tones were pure-tones with the intensity of 10dB above hearing threshold at 7 frequencies with an octave step between 125Hz and 8kHz. The test tones were presented through a headphone and the subjects were asked to describe their subjective expressions of the nature of test tones by using onomatopoeias. The results obtained were as follows: 1) The more various kinds of onomatopoeia were used as subjective expressions in the ears with sensorineural hearing loss and with tinnitus than in the normal hearing ears at each of 7 frequencies. 2) When the onomatopoeias and frequency of description at each of 7 frequencies were analysed, there were discrepancies among 3 groups. 3) When the frequencies of description of 6 representative onomatopoeias at each frequency was analysed, discrepancies were found among 3 groups. Based upon these results, it was concluded that the onomatopoetic expressions for the presented test tones varied among these three groups.
Auditory threshold shifts for air conduction following various air pressure changes in the external auditory canal were examined (“tympanoaudiometry”) in both 11 normal subjects and 24 ears with middle ear diseases. Negative and positive changes of air pressure caused threshold loss for frequencies lower than 2kHz in all normal ears. However, threshold gains for these frequencies were obtained in ten out of 24 ears with middle ear disorders, when the negative air pressure was introduced into the canal. All of the ten ears had congenital or aquired incudostapedial disconnection. In 5 cases no soft tissue connection between the incus and stapes was confirmed during the operations. No threshold change was observed in the tympanoaudiograms after creating small perforation in the tympanic membrane. Air pressure changes of the tympanic cavity were induced by Valsalva and Toynbee maneuvers. Threshold gains were obtained after Valsalva maneuver, but no significant threshold change was observed after Toynbee maneuler. These results indicate that the phenomena were caused by lateral displacement of the tympanic membrane and following movements of the ossicles. Futher study should be performed to clarify the mechanism of the results. However, it's expected that the tympanoaudiogram can be of value in differential diagnosis of the ossicular diseases.