In order to evaluate the usefulness of tympanometry as a screening method of school children a pilot study was performed. With Madsen ZO-72, 187 children (39 in the second grade, 43 in the fourth, 25 in the sixth, and 80 in the seventh) were examined by nurse-teachers of their own schools before otoscopic examination. And 9.5% of them failed to pass tympanometric screening criteria. Of those who had undergone tympanometry, 7.0% were detected middle ear disorders by otoscopic examination, while without tympanometric screening, in only 0.7% of 1602 children pathological findings were observed with otoscope. Using tympanometry in screening programs is based on an assumption that a relationship exists between tympanogram types and the presence of middle ear effusion or other abnormalities of middle ear function. Present screening methods such as pure tone audiometry do not appear to be adequate and therefore we would say that in younger children, if only one method is available, impedance testing would be preferred for the following reasons: 1) it requires less time to complete measurement. 2) it is not greatly influenced by either environmental or motivational factors. 3) the rate of children who cannot be tested is lower. 4) it is quite effective in accurate identification of middle ear problems. 5) it is less affected by test techniques. Such problems as overreferral and inability to detect sensorineural hearing loss were also discussed.
The behavior of a masking transient which indicates that masking of a short signal pulse by a longer narrow-band noise burst is stronger at the beginning of the masker burst than later was investigated. The threshold of signal pulses masked by masker bursts as a function of different variables such as bandwidth, cutoff characteristics and rise time of the masker, and delay time between onset of masker and onset of signal was measured. The results were as follows: 1) There were some overshoots for the tonal signals with a frequency at the upper and lower masking slopes (4 kHz and 1 kHz) of a single narrow-band masker (centered at 2 kHz and bandwidth 1.7-2.4 kHz) and the overshoots increases up to 11 dB. 2) The present data showed that overshoot was increasing sharply as rise time of masker increased from 1 msec to 14 msec and then decreased gradually and exponentially as rise time of masker increased from 10 msec to 130 msec. 3) The results, especially those obtained when signal pulses were located at the upper and lower masking slopes, lead to equal overshoot above threshold. 4) When the frequency separation between main masker (centered at 2 kHz, f1) and the second masking tone (2.4 kHz, f2) was small, the amplitude of the combination band would be at its greatest, and overshoot at lower masking slope (1 kHz) would be masked by the combination band.
The behavior of a making transient which indicates that simultaneous masking of a short signal by a longer broad-band noise burst is larger at the onset of masker burst than later was investigated. The masked threshold of signal pulses as a function of different variables such as rise-fall time of signal and masker, cut-off frequency of masker, frequency of signal, delay time between onset of masker and onset of signal, and duration of signal and masker was measured. The results were as follows: 1) The overshoot depended on the masker components about three critical band away. As a consequence, the spectral effect was not responsible for most of the overshoots. 2) This overshoot increased up to 12dB when masker is white noise. 3) The same overshoot occured at the slopes of high-passed and low-passed noise as well as on the plateau. This means that the overshoot could not be interpreted as the development of the critical band. But the overshoot which can be measured on the center frequency of bandsuppressed noise masker increased. 4) The overshoot could not show any influence of signal duration on the shape of the threshold pattern for longer duration than 20msec. 5) The masked threshold rose up several decibels when the duration of the masker decreased until approximately 50msec. The same high threshold appeared even for 20msec duration. This indicated that the maximal excitation of the masker appeared almost instantaneously.
The middle latency response (MLR) was examined in cats under general anesthesia with nembutal. A longitudinal section from the frontal lobe to the superior colliculi and a transvers section from the mid-line passing the left superior colliculi to the right side, and the same procedure in the inferior colliculi were made. Uni- and bilateral medial geniculate bodies were destroyed by injection of Moljodol (contrast media) and by electrocoagulation. The changes of MLR were recorded immediately and seven days after medial geniculate body destruction, and the areas were histologically examined. The results were as follows: 1) The MLR was generated at the upper level of the superior colliculi. 2) Na component of MLR was mainly related to the contralateral medial geniculate body, and Pa component was suggested to be the compound response from a wide central area.