Bone-conducted ABRs and air-conducted ABRs with a vibrator on the forehead and the mastoid were obtained from 10 subjects with normal hearing. Click stimulation (one cycle of 2kHz, 3kHz, and 4kHz) was introduced through a bone vibrator and an earphone. The wave V latencies of recorded ABRs were compared respectively. Wave V latency of bone-conducted ABR on the forehead was more prolonged than that the air-conducted ABR for stimulation of the same frequency. Also, the latency of bone-conducted ABR on the forehead proved to be longer than that on the mastoid. However, there was no latency difference between the air-conducted ABR and bone-conducted. ABR on the mastoid. Furthermore, the tendency of latency difference was independent from frequency of click stimulation. We concluded that the prolongation of latency in the bone-conducted ABR on the forehead, comparing to the one in the air-conducted ABR, was mainly caused by conduction time from the forehead to the inner ear in the skull. In addition, another contributory factor was a poorer high frequency response of a bone vibrator than an ear-phone.
The unilateral recording of ABRs required masking of the contralateral ear in order to eliminate shadow responses in those whose hearing levels on both ears show a certain discrepancy. The effects of masking of the contralateral ear on ABRs were investigated in 35 patients with confirmed unilateral deafness. In the first portion of this study, the shadow responses were recorded from the deaf ear with clicks of 110dBnHL or 80dBnHL, and masking with a narrow band noise of various intensity levels were applied to the healthy ear. Secondly, ABRs were recorded from the healthy ear with clicks of 60dBnHL or 30dBnHL, and a narrow band noise of various intensity levels was applied to the deaf ear. Results were as follows: 1) The latencies of fast and slow components of shadow responses were prolonged, and their amplitudes were decreased, when the intensity of the narrow band noise for the un-tested (healthy) ear increased. 2) The effective masking may be achieved when the narrow band noise is applied for the un-tested ear with the intensity at around ⌈stimulus intensity for the test ear-interaural attenuation (approximately 50dB)+10dB⌋.
A tone on tone simultaneous masking paradigm was used to determine tuning curves of ABR in rats. Probe stimuli were 0.5, 0.8, 1.0, 2.0, 4.0-kHz short tone bursts. ABR tuning curves were constructed to define masker intensity that resulted in a 50% reduction in probe-elicited wave-V amplitude. The frequency specificity of each probe stimulus was evaluated by Q10 and the maximum masker frequency (MMF) calculated for the tuning curves. Q10's were gradually increased with the increase in rise time. However, a prolongation of the rise time beyond 2 cycles of probe frequency yielded little improvement in Q10. Maximum masker frequencies (MMF) of the tuning curves were not necessarily equal to the frequency of probe without the 2.0-kHz. For the 0.5, 0.8, 1.0-kHz probe, the MMF of the tuning curves showed higher values than the frequency of probe. For the 4.0-kHz probe, the MMF of the tuning curves showed lower values than the frequency of probe. These rusults indicate that the short tone burst stimuli may enable to assess certain auditory function at different frequencies, and they have wider frequencies' spread of the cochlear area around stimulus frequencies.
Four different procedures, Jerger formula, Niemeyer-Sesterhenn formula, Baker-Lilly formula and bivariate plotting method (Silmon et al.), used in predicting hearing level from the stapedial refrex threshold data were compared from 63 normal hearing and 66 hearing impaired ears. With each method, hearing level was correctly predicted in more than one half of all ears, and predictive errors occured in only 2% of them. However, these methods showed a low rate (23-35%) in accuracy predicting a mild or moderate loss. Among these methods, the Jerger method suggested to be adequate to predict the severity of hearing impairment for younger children.
α2-plasmin inhibitor was measured in 36 cases of sudden deafness within 1 week after the onset. As a result, α2-plasmin inhibitor was recognized to be low in cases of poor prognosis regardless to methods of the treatment and hearing level at the first visit. In contrast, the α2-plasmin inhibitor was recognized to be normal in cases of good prognosis. According to these data, the influence of the circulatory disturbance in case of sudden deafness was suggested.
NITTS of the otological by normal young adults was measured under the following conditions in order to obtain the data with which one can predict the occurrence of NITTS in a subject. Method: The exposing noise was a narrow band noine (center frequency at 3kHz) and TTS was measured at 4kHz. Results: 1. It was found to be appropriate to measure TTS2 by every 2dB step of the test sound after the sound of 96dB (SPL) was given for 3 minutes. 2. The exposure of 101dB (SPL) for 3 minutes was found to be inappropriate as a measuring condition because the load was too strong for this study. 3. The exposure of 96dB (SPL) for 1 minute was found to be inappropreate as loading condition, because the load was too weak for this study. The exposure of the save noise for 3 minutes was suitable for this study. 4. After the loading of 3 minute 96dB (SPL) noise, the modal value of TTS2 lay between 4dB inclusive and 6dB exclusive. 5. There was no noticable trend about the test time zone and the subject's sex.