The middle latency response of averaged electroencephalic response to click stimuli were investigated on 8 adults and 8 young children aged from 8 months to 4 years 2 months. The hearing of all subjects were proved to be normal. The results obtained from this studies were as follows: (1) In adults, the great stability was found in the configulations of the response waves and the latency during both awake and asleep, as many authors reported previously. But, there were some inter-subjective variability of the appearance of the response. (2) The response pattern of the young children was unstable during sleep. Especially, Na- and Pa-peak were not consistently detected. It seemed that the appearance of the response tended to depend upon the sleep stage in children. Therefore, the clinical usefulness of the middle latency response, as an objective audiometry for children, may be diminished. (3) It was highly suspected that the origin of Po-peak would be different from that of Na- and Pa-peak.
The electric response audiometries were performed on 7 cases of unilateral temporal lobe lesion, and 4 cases of brain stem lesion or acoustic tumor. Topographic recordings were applied on one case of severely wounded epidural hematoma. The polarity of slow vertex response was reversed on the unaffected hemisphere, but remained unchanged on the affected hemisphere. ERA by the vertex to the ear lobe recordings revealed that the slow responses showed deep P1 and short N1 latencies by the ipsilateral stimulation. On the other hand, they showed deep P2 and flattened N1 by the contralateral stimulation. Those changes of slow response were observed in the cases of 1, 2 and 3. of 6 cases.
The results of EEG-audiometry on 3 cases were reported. EEG gain of 50μv/5mm, 100μv/5mm, and 200μv/5mm were used, and the frequencies of tonal stimuli were 500, 1, 000, 2, 000, and 4, 000 Hz, and intensity of tonal stimuli were 100 phon and 60 phon. The electrodes were attached on left and right frontal area and vertex area. The results were as follows: 1) Sonic responses including K-complex, arousal responses and others were differenciated from sharp waves, slow waves, and spindle activities more clearly on EEG with gain of 100μv/5mm, 200μv/5mm than that of 50μv/5mm. 2) The amplitude of responses to 60 phon stimuli were lower than to 100 phon stimuli. 3) By EEG with gain of 200μv/5mm, 100μv/5mm, the full appearance of sonic responses was most exactly recognised.
Analysis of slow vertex responses evoked by acoustic stimuli was carried out under a series of computarized procedures. These procedures are, (1) power spectrum of the averaged E. E. G., (2) averaged power spectra of the E. E. G., (3) amplitude histogram of the averaged E. E. G., with or without acoustic stimuli. Results; 1. Both power spectrum and averaged power spectra had their peak at around 3Hz when the acoustic stumuli were clearly percieved. On the other hand, they had their peak at around 10Hz, when the acoustic stimuli were not percieved, or when the stimuli were not applied for the subjects. 2. Amplitude histogram of the averaged E. E. G. showed quite normal distribution, regardless of sound perception. However, when the acoustic stimuli were percieved, the distribution showed comparatively slow slope which indicated the increase in the high amplitude components. When acoustic stimuli were not percieved, or not applied for the subjects, the distribution showed steep slope which indicated the increase in the low amplitude component of the E. E. G. These procedures are thought to be useful for the objective judgement of slow vertex responses.
Power spectral and digital filter analysis of auditory slow vertex responses of five normal hearing adults during rest with open eyes, were carried out and power spectral analysis of the wave form by the (±) reference method described by Schimmel carried out. The four components (P1, N1, P2, N2 peaks) of the auditory slow vertex responses at 50dB HL were composed of the frequencies, 1-12c/sec and at 10dB HL were composed of 3-9c/sec. The power spectra of these frequencies changed with the stimulus intensity. Maximum power spectrum of averaged spontaneous brain activity was observed at about 2c/sec.
A system for automatic data storage and retrieval of auditory electric responses by digitamini-computer was developed. This system consists of two disk type memories, A/D converters, analog input terminals, storage type CRT graphic display which is attached to a hard copy and digital high-speed mini-processor. The operation of the system was mainly performed on the basis of on-line real time processing. The analog source signal including of electric responses were stored on a disk in the computer. Then, various commands of requirements for retrieval and output as specified by physcians were given to the computer. This system was accessed by various programs which consisted of threshold detector, checker of base line drift, automatic peak voltage detector and power spectrum analysis. The operator could randomly chosen these programs according to the requirements. And retrieved output results were promptly and accurately shown on the CRT graphic displacy.
The changes of Brain Stem Response (BSR) recorded from vertex of adult cats were studied under a series of lesion experiments with inferior colliculus and several parts of brain stem. The results were as follows: 1. The typical wave forms of BSR in cat consisted of 4 to 6 evoked potentials and the latencies of these potentials were 1.45±0.09, 2.35±0.12, 3.18±0.15, 4.38±0.16, 6.08±0.32, 7.6 msec. 2. BSR was not affected by the using of muscle relaxant and the bilateral destruction at the level of the superior colliculi. 3. The first to third potentials remained unchanged by bilateral aspiration of the inferior colliculi. 4. The fourth and fifth potentials disappeared by aspiration of the bilateral inferior colliculi. 5. The fifth potential greatly diminished by aspiration of the contralateral inferior colliculus which was the opposite side of the stimulating ear. The conclusions are follows: 1. BSR is the acoustically evoked response which has no myogenic component. 2. The first to third potentials are generated at the lower brain stem auditory pathway except the inferior collieulus. 3. The fourth potentials are mainly evoked at the inferior colliculi bilaterally. 4. The fifth potential is mainly evoked at the contralateral inferior colliculus which is the opposite side of the stimulating ear.
Stapedial reflex thresholds (SRT) were measured using Madsen (ZO 72-I) Impedance Meter in 24 subjects with normal hearing, in 23 patients with unilateral sensorineural hearing loss and in 14 patients with symmetrical sensorineural hearing loss. SRT were measured for pure-tone signals of 500, 1, 000, 2, 000, 4, 000 Hz and for white noise respectively (contralateral stimulation). Uncrossed SRT were measured at 1, 000 and 2, 000 Hz (ipsilateral stimulation). SRT in both patients with unilateral and symmetrical sensorineural hearing loss were higher than those in normal hearing subjects for all stimulations. SRT were lower for ipsilateral stimulations than for contralateral ones and lowest for white noise in all the subjects tested. Reversed reflexes (increasing compliance with muscle contraction) and absent reflex were not observed in normal hearing subjects. However, the reversed reflex was observed only in the unimpared ear of a patient with unilateral sensorineural hearing loss. In patients with sensorineural hearing loss, the reversed reflexes were observed only in patients with unilateral hearing loss, but not in those with symmetrical hearing loss. Moreover, this reflex pattern was observed only for ipsilateral stimulations and not for contralateral and white noise stimulations. The incidence of absent reflex was higher in patients with unilateral sensorineural hearing loss than in those with symmetrical hearing loss for both ipsilateral and contralateral stimulations, The difference of stapedial reflex thresholds between pure tones and white noise was greater in normal hearing subjects than in patients with sensorineural hearing loss. At present, measurements of ipsilateral SRT can be applicable in clinical use only for qualitative responses. Further studies will be needed for the quantitative use of the ipsilateral reflex.
The influence of the environmental noises which exist continually or periodically in the everyday life on the pure tone hearing ability were surveyed. In noisy environments such as areas nearby an international airport and areas along the main traffic roads, and in noiseless environments such as agricultural and fishing villages, people living for a long period of time were the objects of this survey. The pure tone hearing test was done using the ISO standardized audiometer and earphone with the frequency from 250 to 8, 000Hz. As to each frequency, the presence of the influence of environmental noises, the dropping tendency of tone hearing ability, and other causes of the hearing impairment were studied and compared with the results of the correlation coefficient of age and hearing loss, and the change of average value with the age. The results were as follows: People living in the areas nearby the airport showed no tendency of pure tone hearing impairment. People living in the areas of loud traffic noises and in agricultural villages showed slight hearing impairment. However, in fishing villages no hearing impairment was observed.
It is well known that noises are the cause of hearing impairment. However, various protective methods have advanced whose fruits are coming up these days. Many studies are done in regard to the influence of occupational noises on hearing ability and most of these reports are clear in contents. Compared with this, reports and estimation methods of the influence of social or environmental noises still do not go over the stage of hypothetical and dissatisfactory contents. We tried experiments on five healthy persons by changing the level and duration of sound field ambient noise to find out its level and duration in which NITTS was produced. In these experiments, various noises including occupational noises were considered to be sources of sound field ambient noises. Five kinds of noises, noise of the passing bullet trains of the Japan National Railways, noise of Boeing B-747 jet planes, the traffic noise on main roads, the metal spray noise within factories, and noise of riveters were chosen. The survey results showed that industrial noises produced an obvious TTS while the train passing noise did not. It was also observed that TTS might be produced slightly by a certain type of noises but might not clearly be produced by another type of noises of higher level.
Two methods were used, and each subject was asked to point a pair of pictures after the stimulus sounds were delivered (choosing picture test), and also each was asked to clapping his hands after the stimulus sounds (clapping hands test). The subjects included 15 children of 3-year-old, 25 of 4-year-old, and 27 of 5-year-old children whose articulation of /t/, /k/, and /t∫/. sounds were normal, and their ability to discriminate these sounds was supposed to be normal. All speech sounds were used as stimuli already reported in the previous study. Correct response more than 75% were obtained in 80% of the children of 3-year-old, 88.0% of 4-year-old, and 96.3% of 5-year-old in choosing picture test and 53.5% of subjects of 3-year-old, 64.0% of 4-year-old, and 88.9% of 5-year-old in clapping hands test. All data were statistically analyzed. The results were as follows: 1) In both methods the correct responses were not obtained in 100% of the children. 2) Clapping hands test was more difficult than choosing picture test. 3) Choosing picture test were suitable over 3 years old. Clapping hands test were adequate to children 5 years old.