THE RELATIONSHIP OF MIDDLE EAR PRESSURE TO HEARING IN AVIATION,

A study of normal ears during relatively slight increases in ambient pressure has revealed that unless the middle ear is properly ventilated significant loss of hearing acuity occurs. The tests, made in the low pressure chamber, indicate that a descent from 5000 to 3000 feet without compensation of middle ear pressure reduces hearing acuity from 25 to 30 decibels in the low frequency range 128 to 2048 c.p.s. and a descent from 2000 to 1000 feet reduces hearing 15 to 20 decibels. In addition there occurs the illusion of fading of a constant intensity stimulus. Since the loss in hearing acuity occurs in the frequency range utilized for both the radio range beacon signal and the voice signal, auditory orientation may become faulty if middle ear pressures are not equalized properly. The fact that such relatively slight changes in pressure may have large effects should be brought to the attention of all personnel concerned with instrument and radio orientation in aircraft. Author