Influences of various parameters of stimulus sounds on evoked otoacoustic emission (e-OAE) were investigated in 10 normal hearing ears with type A tympanogram. The stimulus sounds were tone-bursts with the frequency at 1.5kHz and the intensity of 35dB (nHL). It was examined whether changes in the polarity, inter-stimulus interval and duration of stimulus sound might affect e-OAE wave form. The results obtained were as follows; 1) The polarity of e-OAE wave form coresponded to that of the stimulus sound. However, the change in the polarity of stimulus sound did not affect the amplitude, latency or duration of e-OAE. 2) The change in the inter-stimulus interval did not affect any parameter of e-OAE. 3) The change in the duration of stimulus sound did not affect e-OAE amplitude. 4) The e-OAE latency became longer as the total duration of stimulus sound became longer. However, the degree of elongation in the e-OAE latency was less than that in the total duration of stimulus sound. 5) The duration of e-OAE could depend on the total duration of stimulus sound.
Two metal acoustic probes with a different length and diameter were made to investigate the effect of the probe-shape upon the acoustic properties in the evoked oto-acoustic emission (OAF). The acoustic distortion was more prominent in the longer probe with a smaller diameter than the shorter one with a longer diameter. The higher frequency stimulus was not so distorted as the lower one in both probes. It is clear from our present observation that the shape of the ear probe is closely related to the presence or absence of the artefacts. Further studies are necessary to determine what shape of the probe is ideal to minimize the artefacts in recording OAE
After recording evoked otoacoustic emissions (eOAE) to click in 154 ears of 90 patients with cochlear deafness by using ILO88 which was made by Kemp and Bray for recording and analysing eOAE easily, the relationship between eOAE and severity of cochlear deafness was studied. The results obtained were as follows. (1) The severity of hearing loss and eOAE detection. If we judge the presence of eOAE with two criteria, the detection of eOAE wave and the reproducibility more than 40%, eOAE was detected with the reliability of 94% in 81 ears with the mean hearing loss at the 4 frequencies from 500Hz to 4000Hz less than 35dBHL. eOAE was not detected with the reliability of 89% and 92% in 73 and 63 ears with the mean hearing loss at the 4 frequencies more than 35dBHL and 44dBHL, respectively. eOAE was not found with the reliability of 94% in 64 ears with the mean hearing loss at the 2 frequencies 1000Hz and 2000Hz more than 40dBHL. (2) The severity of hearing loss and eOAE power. In 84 ears with eOAE detection, negative correlation (r=-0.44) between the severity of hearing loss and eOAE power was found when total echo power and highest peak power at the frequencies from 1000Hz to 2000Hz in FFT pictures were used as an indicator of eOAE power. From the results mentioned above, we concluded that ILO88 was useful for screening of cochlear deafness with the mean hearing loss more than 35 or 40dBHL at the frequencies from 500Hz to 4000Hz.
Evoked otoacoustic emission (e-OAE) was investigated in 24 cases of surgically proven unilateral acoustic nenroma and 24 normal hearing subjects. The e-OAE was elicited by the stimulation of tone bursts with the duration of 3ms at 1kHz and 2kHz. The responses were averaged 512 times with the analysis time of 20ms. The results obtained were as follows; 1) The e-OAE pseudothreshold was within the normal range in a few tumor-bearing ears, but elevated beyond that of normal hearing ears in the other tumor-bearing ears. 2) The interaural difference of e-OAE pseudothreshold was within 5dB in about 70% of the recordings of normal hearing subjects but it was within 5dB in only 30% of the recordings of acoustic neuromas. 3) The e-OAE pseudothreshold in tumor-bearing ears was significantly higher than that in normal hearing ears (p<0.05). 4) The correlation coefficient between the e-OAE pseudothreshold at 1kHz and that at 2kHz was estimated. There was a high positive correlation between them in normal hearing ears and unimpaired ears of acoustic neuroma cases, but the correlation coefficient deteriorated in tumor-bearing ears. 5) In tumor-bearing ears, there was a slight positive correlation between the e-OAE pseudothreshold at 1kHz and the pure tone hearing level at 1kHz. However, no clear correlation was found between the e-OAE pseudothreshold at 2kHz and the pure tone hearing level at 2kHz. 6) There was no clear correlation between the e-OAE pseudothreshold and the maximum speech discrimination score in tumor-bearing ears. 7) There was no clear correlation between the tumor size and the pure tone hearing level in tumor-bearing ears. 8) There was a slight positive correlation between the tumor size and the e-OAE pseudothreshold at 2kHz in tumor-bearing ears. while no clear correlation was found between the tumor size and the e-OAE pseudothreshold at 1kHz. 9) Based upon these results, it was suggested that the pathophysiology of hearing impairment could be so intricated in acoustic neuromas. 10) The e-OAE recording could be one of the supplemental diagnostic tools to detect acoustic neuromas, especially in cases with profound hearing loss in which the ABR conld not be applicable, because the e-OAE could be obtained in some of these cases in spite of the profound hearing loss.
The threshold of the evoked otoacoustic emissions (EOAE) of normal hearing subjects was measured by using otodynamic analyzer ILO88. The subjects consisted of normal hearing individuals, tinnitus without hearing loss, low tone deafness and hyperacusis. The hearing level of them was within normal limit at the measurement. The results obtained were as follows. 1. There was no difference in threshold of the EOAE between normal individual group and other subjects. But significant difference existed among the individuals. 2. The interaural difference of the threshold of EOAE might be more appropriate for the clinical use than the threshold itself. 3. Because of the phase lock effect to the spontaneous otoacoustic emissions (SOAE) by the stimulative tones, the threshold of the ears with SOAE was smaller than that of the ears without SOAE. (54.6 vs 65.3 dB SPL) 4. The further informations of the inner ear might be obtained by the analysis of frequency spectra of EOAE.
Generation mechanism of evoked otoacoustic emissions (e-OAE) is considered as follows: A sound produced by a probe earphone is transmitted through the external auditory meatus, eardrum ossicular chain and cavities, and excites some portion of a cochlear; amplified basilar membrane vibrations achieved by an active electromechanical involvement of the organ of Gorti are transmitted reversely to the external auditory meatus, and detected by a probe microphone as small amplitude sound pressure vibrations. Therefore, the effect of middle ear upon e-OAE seems to be very large. In this paper, applying e-OAE measuring system and Middle Ear Analyser which we have developed, e-OAE and middle ear dynamic characteristics of normal subjects were measured, and an attempt was made to clarify the correlation between the input sound frequency where e-OAE was the most distinctly detected and the middle ear dynamic characteristics. The following conclusions were obtained. (1) The input sound frequency where e-OEA is the most distinctly detected is nearly coincident with the resonant frequency of the middle ear where a volume displacement of the eardrum is maximum. (2) The dominant component of e-OAE frequency almost coincides with the input sound frequency.
The delay time of evoked otoacoustic emissions (e-OAE) is not twice as long as the travelling time along the basilar membrane as expected by reflections. But the long delay of e-OAE can be explained by assuming Bragg's reflections in the one-dimentional model of the basilar membrane. The computer simulation provided a reasonable explanation for the following features of e-OAE: (1) the relation between the width of the exciting tone burst and the delay time of e-OAE; (2) the frequency dependent delay time (about inversely proportional to frequency); (3) the input-output level dependence; (4) the multiple echo.
Latency of evoked otoacoustic emissions was measured in 20 ears using tone burst stimuli. The latency was calculated from the first local peak of autocorrelation function, which is one of possible definitions of the latency. It was shown that the higher the central frequency of the stimuli, the shorter the latency of the emissions. This result was in agreement with some previous reports by other researchers. It was also noted that variation of the latencies among the ears was relatively large and ±1SD range was 3msec for 1kHz stimuli.
Evoked otoacoustic emissions (e-OAEs) elicited by 4 kinds of 1kHz sinusoidal stimuli with the total duration time varied from 2 ms to 6 ms, were recorded from 21 normal hearing ears. The e-OAE waveform variation caused by change in the stimulus duration was investigated. There was a tendency that the peak latency represented the time after stimulus onset when the e-OAE amplitude was maximum, was delayed with elongation of the stimulus duration in most of ears. And, judging from this peak latency delay and the whole response wsveform, the changes of the waveforms with those of the stimulus duration were divided into two different types. One type was that it changed as if the e-OAEs were offset responses and another type was not so. However, the study using compound waveforms made by the technique superimposing waveforms, revealed that the e-OAEs were not offset responses even if they seemed to be such responses. Namely, it was considered that the e-OAE waveform recorded actually was produced as a result of reciprocal interference of responses elicited by each cycle of the stimulus sound.
A 10-month-old baby with a continuous high-pitched tone, in the left ear, which was objectively audible was examined. The tone was not pulsative. The baby had a sensorineural high tone loss, which was found by conditioned orientation reflex audiometry and auditory brainstem response audiometry. A single spontaneous otoacoustic emission (35dBSPL) was noted at 11250Hz in power-spectrum. The emission was similar in frequency to the tone simulated by his mother and examiners as a high-pitched objective tinnitus.
The emission cochlegram was investigated in 11 cases of surgically proven unilateral acoustic neuroma. Stimulus sounds were tone-bursts with the duration of 3ms at 5 frequencies between 1kHz and 4kHz. The results obtained were as follows; 1) The emission cochleograms showed similar configurations in the unaffected ears, but showed various configurations in the tumor-bearing ears. 2) The averaged emission cochleogram of the unaffected ears showed the high-tone abrupt loss type of configuration, while that of the tumor-bearing ears showed the high-tone gradual loss type due to the elevation of pseudothreshold between 1kHz and 2kHz. 3) The comparison between pure tone audiogram and emission cochleogram could enable to speculate the pathophysiology of hearing loss in each case of acoustic neuromas. 4) The pathophysiology of hearing loss might differ on the different cochlear partitions in some tumor-bearing ears.
100Hz narrow-band evoked oto-acoustic emissions (EOAEs), band-pass filtered by a 100Hz of bandwidth in frequency regions from 1.0 to 2.0KHz, were recorded from 5 cases of sudden deafness. 100Hz narrow-band EOAEs could be elicited even from ears with the hearing threshold greater than 40dB HL. Echoes with the short latency within 10msec following the stimulus onset and the frequency content 1.0 to 1.6KHz have a tendency to persist in ears with severe hearing loss. In general, the recovery of EOAEs occurred from echoes with the lower frequency content and the shorter latency, and thereafter echoes with the higher frequency content of 1.6 to 2.0KHz or the longer latency above 10 msec appeared with the improvement of hearing hearing loss. The EOAEs amplitude also increased with improving loss. The hearing loss in all five cases with definite EOAEs recovered to normal level within 20 dB HL, at least, in the frequency range between 0.125 to 0.5KHz.
The FFT analysis of spontaneous otoacoustic emissions (s-OAEs) and evoked otoacoustic emissions (e-OAEs) were studied in 12 ears of 6 normal hearing subjects. The s-OAEs were recognized in 4 ears, and the frequencies of s-OAEs were almost corresponded with the frequencies at which the e-OAE could be recorded most apparently. And also, the e-OAEs in these 4 ears were continual. The results of the analyses of the e-OAE sound pressure curve under the same stimulus sound pressure level indicated that the e-OAEs tend to appear at the frequencies of s-OAEs. And also, the comparison between expected e-OAE power spectrums and actually measured power spectrums, and the FFT analysis of e-OAE showed the same result. From the results of averaging data along the time axisunder no stimulus sound, the phase of s-OAE could not be synchronized under this e-OAE recording conditions. When the phase of the stimulus sound was changed, e-OAEs at the frecuencies of s-OAEs also appeared as the phase follwing responses. Therefore, in the ears with s-OAE, the s-OAE might be synchronized with the stimulus sound as the trigger, and as a result, e-OAE was recorded to be continual.