Abstract
The type of apparatus employed in this series of observations has been previously described in this journal. We submit some very general conclusions based on the observations made on individuals with known sensitivity for air-transmitted sound. A continuous tone scale was employed and the threshold approached from below as in the air tests.
Sensitivity for tone-transmission of sound varies a great deal more than that for air-transmitted sound, and is not definitely related to it. The sensitivity at any given frequency is not a criterion of the sensitivities at other pitches. We found about 500 v. p. s. the least variable. Areas of marked decrease in air acuity are similarly registered through the bone.
In normal ears the hearing is most acute at normal pressure for both air and bone transmitted sound. The development of plus and minus pressures in the air of the external auditory canal decreases acuity for both series of tests, and leads to the conclusion that the cranio-tympanic conception of sound transmission is probably the correct one.
In comparing the acuity for bone-transmitted sound, with external canals open, as opposed to external canals occluded, some rather disconcerting findings were made. The individual with the greatest sensitivity through the bone with the ears open showed the least advantage on closing the external canals. It was also observed that the enhancement in bone transmission due to occlusion of canals becomes less pronounced as the pitch rises, and is most marked in the low part of the tone scale.
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