(The) study of reference hearing levels in Koreans
Accuracy in determing auditory thresholds is crucial for identifying persons with decreased hearing acuity, particularly in view of the ever-expanding growth of hearing conservation programs, diagnostic clinics and the increased use of industrial audiometry.
The results of hearing tests are important in deterring the necessity for medical treatment, educational placement, acceptability for employment and the advisibility of a hearing aid.
The accuracy of hearing tests is directly related to a number of factors, such as the training and experience of the operator, environmental noise and the cooperation, and attention of the subject. Of equal importance is the state of calibration of the audiometer.
Individuals differ from one another, and normal hearing for the clinician turns out to be a range, not a single value, even for subjects of the same age and sex.
So it is required to have standardized reference hearing threshold for normal person, audiometric equipment and procedures. Although American Standards Association (1951) and International Standards Organization (1964) levels have been universally adopted, various world countries have the reference hearing levees of their own. But there are no documents about any standards for reference hearing levels in Koreans with well-calibrated audiometer.
The purpose of the present study is an attempt to determine the reference hearing levels in Koreans, and accordingly to contribute to be a fundamental data for the otological research in Korea. In accordance to this study, it is also examined to study about the threshold changes by means of various psychoacoustic audiometric procedures.
Test subjects were well-motivated 300 persons from 18 to 24 aged group whose medical history showed no evidence of otologic diseases and other abnormality. The studies were all carried out under carefully controlled conditions of ambient noise and employed up-to-date psychoacoustic method (Hughson-Westlake method). All subjects were tested on 11 frequencies with Maico Model MA-10 audiometer which was calibrated with Bruel & Kjaer Sound Level Meter, artificial ear and mastoid using 3 crosses testing.
The results were summarized as follows:
1. Threshold measurements using a descending technique yielded lower (better) threshold by average 1.2 dB than those obtained with an ascending technique. 2. Comparing on the basis of the first and second test, threshold measurements show poorer threshold for the second test at low frequencies below 1000 Hz by
average 1.2 dB than those obtained for the first test, bet conversely at high frequencies it shows lower (better) threshold by average 1.8 dB.
3. Generally average 1.5 dB of better threshold through all frequencies was obtained by giving enough instruction for the test.
4. There was no significant difference for threshold measurements between useful finger observation method and button method as a hearing response.
5. The reference hearing threshold in Koreans revealed average 6.7 dB of better threshold than American Standards Association levels, but average 5.2 dB of poorer one than International Standards Organization reference levels. So Korean reference
hearing threshold is known to be approximately in median value between ASA and ISO levels.