Delayed auditory feedback effect (DAF-effect) on speech and acoustic reflex were examined in 40 normal subjects and 45 patients with brain damage of the left and right hemisphere or the brain stem. The results were as follows: 1) There were two types of DAF-effect, that is, positive and negative in normal subjects. The acoustic reflex in the positive DAF-effect subjects revealed the lower threshold and the larger amplitude than those of the negative DAF-effect ones who showed poor acoustic reflex. 2) There was the tendency that the patients with brain stem damages showed negative DAF-effect and poor acoustic reflex, and the patients with damage in the right hemisphere showed the positive DAF-effect and better acoustic reflex. 3) It was concluded that there was the correlation between the DAF-effect and acoustic reflex.
Power spectral analysis and digital filtration of the auditory middle responses (AMR) to click stimuli in six adult subjects with normal hearing were performed. The spectral analysis revealed that the dominant frequency components of the AMR were located at 30 to 50Hz. Frequency ranges below 30Hz in the spectrograms probably resulted from the spontaneous activities of the brain. These frequencies often disturbed the detection of the main peaks of AMR, especially Pa and Nb. A small peak at 100-140Hz in the spectrograms was supposedly due to the auditory brain stem responses (ABR) and the earliest part of the AMR, that is, a negative-positive deflection which followed the ABR. After the low frequency brain activities were completely eliminated with high pass digital filtration at 30Hz, Na-Pa-Nb components and a positive peak with latency of 60-70msec were constantly recognized. On the other hand, when high pass filter was set at 40Hz, the positive peak at 60-70msec disappeared and Nb was followed by two successive positive peaks appearing at 50-55msec and 80-85msec after the onset of stimulus.
Stability and reversibility of each component of middle latency response (MLR) were studied at the stimulus intensities just above the behavioral hearing thresholds. MLR was recorded at the intensity of 30dB, 20dB, 10dB, and 0dB above the hearing thresholds, and 5 test-retest trials were carried out at every stimulus level in 8 normal hearing human subjects. The results were as follows; 1) The early components of MLR, namely, Po, Na, Pa components were fairly stable at 20dB above the hearing thresholds 2) However complete reversibility of their components could not be obtained even at 30dB above the hearing thresholds. 3) When MLR is used as one of the neurological examinations and the patterns of MLR components are discussed, the intensity of acoustic stimuli should not be lower than 30dB above the behavioral hearing thresholds. However, it is reasonable to mention that the response threshold should be approximately 20dB above the hearing level when MLR is used for audiological examination.
Detectability and latencies of ABR components were studied at several intensities of click stimuli above psycho-acoustical hearing thrershold. And successively the response thresholds of waves 1 to 4 were compared with the wave 5 response threshold (ABR response threshold) in normal hearing human subjects. The results were as follows: Comparing the delectability of the ABR components at the several intensities above the psycho-acoustical hearing threshold, 1) Stability of the response threshold between wave 3 and wave 5 seemed remarkable. And wave 3 appeared at approximately to to 20dB above the wave 5 response threshold. 2) However each response threshold of wave 1, 2 and 4 showed remarkable discrepancy. Conclusion: In those patients whose acoustical hearing threshold was not obtained, the detectability of wave 1 to 4 above the wave 5 response threshold should be taken into consideration carefully when ABR patterns were discussed.