Observations On Hearing-Acuity For Bone-Transmitted Sound.

The writers have demonstrated that bone-transmitted sound follows at least part of the pathway to the labyrinth taken by air-transmitted sound. It has also been determined that the acuity for air-transmitted sound is not necessarily a criterion for the bone-sensitivity, or vice versa. The writers have reported elsewhere 1 the quantitative findings in two cases of deafened individuals who claim to hear better in a noise. While these two individuals belong to the paracousis Willisi type, they were found not to have unusual bone-sensitivity. Deafened people do not really hear better in a noisy place; rather it is the normal individuals who do not hear so well.

Acuity for Air-Transmitted Sounds. Figures 1 and 2 show the acuity for air-transmitted sound of the two subjects included in this report. The acuity is given in terms of the logarithm of the reciprocal of the necessary intensity for hearing, and a difference of one unit in sensitivity corresponds to an intensity ratio of 10, two units to 100, etc. The average sensitivity of normal hearing people is also shown.

The sensitivities of the two ears of subject A are about alike and average about 3.0, while the average normal curve has a height of about 8.5, giving a difference of 5.5. This would indicate that it takes about 10^5.5, or about 300,000 times normal intensity for subject A to hear. Similarly subject B requires about 100,000,000 times normal intensity for the right ear, and 3,000,000 times normal intensity for the left ear. Qualitatively, subject A by paying attention, experiences no marked difficulty in conversing with normal people. On the other hand, normal people must speak very loudly in order to make subject E understand them.