STUDIES ON BONE CONDUCTION AUDIOMETRIC MEASUREMENT

Abstract

Author studied the logics of masking bone conduction, and the phenomenon with regard to Weber test, especially from experimental and clinical stand point. Results obtained are as follows :1) In order to mask the ear not to be tested, it is necessary to bear in mind the limitation of effectiveness of masking the ear dependent on the noise level, especially the limitation to the maximum noise level of the audiometer concerning on the three types of cases, i. e. binauraly perceptive. conductive deafness and one ear conductive the other perceptive. These limitation is able to be demonstrated by fomulation.2) Bone conduction measurement under deficiency of masking represents shadow hearing curves which coincide with some limitation curves of masking.3) Over masking cosists of peripheral and central elements, the former is masking opposite ear by the crossed air and bone conduction, the later through the crossed auditory nervous pathways.a) The central masking shows some frequency characteristics which are not remarkable as peripheral masking.b) The degree of effectiveness of the central masking is in proportion to the intensity of noise.c) Peripheral over masking tends to rise in the tested ear suffered from conducrive deafness, central over masking tends to rise at the case of which difference by bone conduction between both ears is large.4) In Weber test a questionable point is that sometimes bone conduction may not be heard in the better ear by bone conduction. To study the etiology of this paradoxical phenomen, placing air conduction receivers on the both ears, either ear was heard tones near the threshold level, and the existence of false judgement on the audible side was proved.5) In the both ears the least differenc between the intensity of two tones from which the feeling to hear in either ear arises is larger at higher intensity level than at lower, then Weber test is reasonable to be made at lower intensity level.6) In one ear, the least intensity differences between two tones being able to differ are larger at the higher intensity level than the lower, and this relation also quantitatively coincides with the former experiment in the both ears.