Diagnostic values of bilateral ABR recording were studied from the test results of 69 patients with endocranial lesions. Compared with unilateral ABR recording, the predominant incidence of abnormality by bilateral ABR recording was shown in all cases except for the cases of acoustic tumor which showed an equal incidence in the both methods. From the above mentioned results, it was considered that bilateral ABR recording was more useful for diagnosis of brainstem disorder than unilateral ABR recording.
Serial changes of the auditory brainstem response (ABR) which finally exhibited no response were studied. The ABRs were recorded repeatedly from patients who were in deep coma. The wave became disappeared from the later components of the ABR, and only wave I remained before all components were abolished. The latency prolongation and amplitude reduction of wave I were often observed in a short period of time, then wave I abruptly disappeared. Before abolishment of ABR waves, occasionally there was a new wave in which the latency was shorter than wave I. Then electrocochleogram (ECoG) was recorded in patients who showed only wave I response in order to identify the origin of this new wave. The latency and behavior of the new wave to the anoxic state of the cochlea were similar to those of summating potential (SP) in ECoG. Thus the new wave in ABR was thought to be SP.
The effects of the electric stimulation of crossed olivocochlear bundle (COCB) on the ultrasonic (98.8kHz) evoked cochlear nerve action potential (UAP) were investigated and the results were compared with its effects on the AP evoked by 12kHz tone bursts (burst AP) in 5 guinea pigs. As COCB stimulation, the rectangular pulse trains were repeatedly applied to the animals before each tone stimulus at the floor of the fourth ventricle with an isolated bipolar electrode was delivered. The responses were obtained from the round window and analysed after averaging. With COCB stimulation, the burst AP amplitude showed a significant decrease, and its latency was slightly elongated, especially in the responses near threshold. On the other hand, no effect of COCB stimulation was detected in the amplitude and the latency of UAP. According to the results of our previous experiments, the receptors of ultrasonic sound were thought to have rather wide distribution in the basal turn of cochlea, which should have the greatest efferent projection density and consequently should effectively be suppressed by COCB stimulation. The result of this study will become one of the circumstantial evidences in favor of the hypothesis that the transduction of ultrasonic sound is performed by IHC of the basal turn of cochlea without any modulation or enhancement by normal OHC function.
Detectability and latencies of ABR components were studied. The influences of the slow component of ABR on wave II and IV were also studied on unilaterally deaf subjects. The results were as follows: 1) Detectability of the wave II was high and its stability was almost the same with those of wave I, III and V with the click stimuli of intensity of 70dBnHL. 2) The wave IV was greatly influenced by the slow component of ABR with the same stimuli. Therefore, when the low cut of the filter. was fixed about 100-200Hz and the slow component of ABR was neglected, the wave IV was also the very stable and reliable component.
Phase spectral analysis of the auditory brainstem responses (ABRs) to click stimuli for different intensity levels and under non-stimulus condition were performed in cats. In each stimulus level, an ensemble 10 patterns of ABRs in each animal, each consisting of 200 sweeps, were collected for calculating phase variance using fast Fourier transform. The phase variance for selected frequency components making up the ABRs was compared to the ABR morphology, in order to discuss the significance of phase spectral analysis for the automatic detection of response threshold. It was found that the phase variance was a good predictor of ABR signals. From the result, this procedure was expected to apply to the automatic ABR threshold detection.
A series of studies on human auditory laterality suggested the presence of a switching mechanism in human brainstem that automatically transmits auditory signals to either the right or the left hemisphere, depending upon the physical properties of the sound. The purpose of this study was to identify physical parameters that determine this laterality. Some environmental and artificial sounds for which the hemispheric dominance had been previously clarified by both Tsunoda's method and the auditory evoked potential method, were analyzed by analog and digital signal processing techniques. As the results, in normal Japanese, the right hemisphere was found to be dominant for the sounds with the following physical characteristics: (1) single formant (or formant-like structure) or simple (logarithmic) attenuation in higher frequency ranges. (2) two or more formants (or formant-like structures) in harmonic relations. (3) small pitch fluctuations and rich harmonic structures, particularly, when sounds consist only of harmonic tones.
The auditory brain stem response (ABR) is a composite of several sequential fast wavelets and a positive slow wave. Relationships between both of each component and cochlear function are not completely clearified. There have been two principal suggestions for specific origin of the click response. One view is that most parts of the cochlea are important for generation of the evoked response. The other view is that evoked response reflects mainly the activity of the most basal part of the cochlea. So, thresholds and waveforms of the ABRs evoked by clicks were examined in hearing-impaired subjects. The results were as follows. 1) The threshold of the click evoked ABR reflected the cochlear function of the most sensitive area from 1kHz to 8kHz. 2) The fast waves were evoked only in the limited part of the cochlea covering high frequencies, whereas, the positive slow wave was evoked in the more expanded part of the cochlea covering both low and high frequencies.
Effects of analog filtering on the auditory middle latency responses (MLR) in young children synthesized by a complex waveform synthesizer were studied. For obtaining analog-filtered responses, a Butterworth filter was used with a passband from 20 or 25Hz to 175Hz and a roll-off slope of 24dB/octave. Analysis of the analog-filtered responses revealed that the first negative peak (Na) and the second positive peak (Pa) in the filtered response were resulted from the filter-produced damped oscillations of the preceeding peaks of ABR (Po) and Na in the unfiltered responses, respectively. Likewise, the second negative peak (Nb) and the third positive peak (Pb) in the filtered responses were composed of the filter-generated oscillations triggered by Na and the later components of the unfiltered responses. The results showed that the MLR waveforms in young children were radically distorted by analog high-pass filtering at 20-25Hz with a roll-off slope of 24dB/octave. It can be meaningless to compare directly these filtered responses with the unfiltered ones.