Abstract
In an attempt to study the normal fluctuation of hearing threshold, the author tested hearing acuity of normal subjects every other hour within one day or at the same hour every second week. The results were as follows;
1. In the every other hour test within a day, normal ears showed 19 dB fluctuation of the threshold at maximum.
The fluctuation was greater in low and high frequencies, while it was lesser in the middle frequency range.
2. In about two thirds of the subjects tested there was a tendency for the threshold to elevate at about 1 to 3 p. m. and also at 6 to 8 p. m., which appeared to be related to meals.
3. The Fourier analysis of the results revealed a relative cycle of 2.33 3.50 and 4.67 hours.
4. The fluctuation within a day was greater than that of every second week.
5. Using a JIS standard audiometer and receivers the author found it difficult to determine the real threshold in a subject, for normal ears often showed -10 dB value in 3000 to 6000 Hz. range.
