Auditory brainstem response elicited by tone bursts were recorded from the scalp of human subjects. Response alternations produced by changes in the duration time were evaluated. The latency and the amplitude of wave V and VI were increased with increase of tone bursts duration, whereas latencies of wave I to III (and IV) were less increased, and the amplitude of them tended to decrease. These changes were not caused by the decreasing interstimulus interval, but by the increasing stimulus duration. Although, there was no distinct explanation for the changes of ABR recording of slow component had suggest that the changes in the slow component may play an important roll.
The auditory brainstem responses (ABRs) obtained from 28 normal healthy adults were studied using the ipsilateral and contralateral recordings from the positions of the vertex and the mastoid to monaural stimulation. The results were as follows: Each wave of ABRs recorded by ipsilateral and contralateral derivations to stimulation site showed slightly significant differences. Comparing the ipsilateral and contralateral data, the latencies of waves II and V showed a slightly small reduction in the ipsilateral recording, while these of waves III and IV showed a small increase. Next, the distributions of potentials and latencies of waves II to V were investigated from ABRs with different electrodes in the mid-coronal array of the scalp and non-cephalic reference electrode on the seventh cervical vertebra (C VII). The results of latencies showed the reverse relation to the data obtained from the ipsilateral and contralateral recordings using the reference electrodes on each mastoid. These facts suggest that the comparable differences of latencies in the bilaterally recorded ABRs are explained by the pseudo-phenomena of differential recordings, which the phase delayed or advanced potential propagated to each mastoid being reference electrode position.
Both components of the ABR, sequential fast wavelets and positive slow wave, originate from different anatomical structures with different electrophysiological mechanisms. Origins of the positive slow wave were studied using some destructive methods in rats. After the mechanical destruction of the right cochlea, lesions were made in several parts of the auditory brain stem structures. The wave forms of the positive slow wave and the fast wavelets were observed before and after the destructions. The lesions were examined by serial sections for microscopic examination. Considering the results, the following conclusions were obtained: 1) The positive slow wave might have its generators in the several parts of the brain stem auditory pathway, that is, ipsilateral cochlear uncleus, contralateral superior olivary complex, contralateral nucli of the lateral lemniscus and contralateral inferior colliculus. 2) On the contrary, cochlea, ipsilateral lateral lemniscus and ipsilateral inferior colliculus are not essential to generate the positive slow wave. It is presumed that the positive slow wave is likely to be generated by the gray matter in the brain stem structures and that the sequential fast wavelets are generated primarily by the white matter.
Power spectra of normal and abnormal ABRs were evaluated. In the normal ABRs, the spectrograms were composed mainly with three major peaks at around 100-300Hz (A peak), 500-700Hz (B peak) and 1000-1100Hz (C peak), (A peak>B peak>C Peak). In the abnormal ABRs, their power spectra revealed the different distribution from the normal ones, a shift of the each peak toward lower or higher frequencies, and the changes in power balance of the peaks. And the morphological abnormalities of ABR were classified by the distinctive feature of their spectrograms. Power spectral analysis could be expected to be able to apply for clinical diagnosis in the neurological field.
Slow vertex response (SVR) has been applied for the objective audiological examination of infants. However, there are unsolved problems concerning the modality of SVR. Especially the generator of SVR has not clearly been defined. The purpose of this study is to investigate the generator of so called “auditory evoked cortical response” in animal experiments. Evoked potentials were recorded between the vertex and the ear lobe. The conclusions were as follows: 1. SVR in cats revealed similar modality to that of human subjects. 2. P2 and N2 components were greatly influenced by anesthetics. 3. Bilateral primary auditory cortex were closely related to the generator of P2 and N2 components. 4. P1 and N1 components were mainly produced at the subcortical area including the brain stem.
In order to investigate the cause of the changes of the cochlear potentials in vitamin D deficiency rats, namely prolongation of N1 latency, depression of CM amplitude and elevation of CM threshold, Ca2+ concentration in perilymph was measured by Ca2+ selective microelectrode. The result was that Ca2+ concentration in perilymph showed 3.3×10-4M (n=4) in vitamin D deficiency rats and 7.4×10-4M (n=4) in controls and its ratio to serum Ca2+ concentration exhibited 63% and 57%, respectively. The cause of the decrease in perilymphatic Ca2+ concentration in vitamin D deficiency rats was thought to be due to the secondary effect of the decrease in serum Cas2+ concentration. But the gradient of Ca2+ concentration between perilymph and serum was maintained to be normal in vitamin D deficiency rats. It is postulated that this secondary decrease of Ca2+ concentration in perilymph and possibly in endolymph had an effect on the acoustic transduction and the synaptic transmission, by which the alternations of N1 and CM were induced.
The auditory response in which the eyes were opened slowly when the sound stimuli were presented to the subjects soon after they are going to fall into sleep was called as the auditory eye opening responses at falling into asleep (AEOR: Suzuki & Notoya, 1980). AEOR was analyzed by electrophysiological techniques. Subjects were two women with normal hearing. AEOR was evoked by warble tone (1kHz, 3kHz 55dB (A)). The results obtained were as follows: 1) AEOR was evoked in the later part of stage wakefulness and the earlier part of sleep stage 1. 2) The latency of AEOR recorded by EMG of eyelid is about 600ms. 3) The latency of AEOR recorded by EEG is about 400ms. 4) The change of EEG were α-blocking and presenting α waves. These results suggest that AEOR is a kind of arousal or searching responses which were controlled by higher levels, and distinguishable from auditory other reflexes such as startle reflex.
In order to obtain the basic data on effects of noise on speech hearing, the following experiment was performed. With the several combinations of sound pressure level, mixing of 57-S word list and broad band noise were examined. The results were as follows. Data of articulation score by 57 word list was same as that of 57-S word list under several dB of speech level of 57 word list. On the condition of signal vs noise ratio being 10dB in the 57-S word list, articulation score was 10% higher than that of 57 word list.
Dichotic listening tasks, in which competing signals were presented to both ears, were used to study the higher central auditory function and dysfunction. Dichotic speech listening technique revealed the hemispheric lateralization of the brain. The right ear advantage (REA) for speech perception is the index of left-hemispheric language dominance. The study was to elucidate emergence of the dichotic REA for Japanese stop consonants and vowels presented simultaneously to the left and right ears. The competing task I (CV versus CV) and task II (CV, CV versus V, V) were performed for twenty right-handed listeners with normal hearing sensitivity. The results were as follows: 1) The identification score of Japanese stop consonants that the ending of CV monosyllables were cut off into 192.0ms in the duration, were 95.3% at the left ear and 95.4% at the right ear. 2) In dichotic listening of paired stop consonants, the proportion of REA was significantly larger in short duration group than in long duration group. 3) The advantage for the right ear was larger for voiceless stop consonant in simultaneous competing situation. 4) The identification of vowels presented to the right ear was 78.0% in dichotic listening of stop consonant versus vowel. In the listening situation, it was showed that Japanese vowel signals travel the path from the right ear to the left hemisphere and could be identificated and recognized.