Simultaneous cancellation of air and bone conduction tones at two frequencies: Extension of the famous experiment by von Békésy

Cancellation experiments between air conduction (AC) and bone conduction (BC) tones were conducted at two frequencies (0.7 and 1.1 kHz) and three levels (40, 50, and 60 dB HL) in three subjects. The tests were divided into three categories: (1) single tone cancellation, (2) simultaneous cancellation of two tones, and (3) cancellation of one tone while a disturbing tone was present. In total, each subject performed twelve cancellation tasks. The hypothesis is that the AC and BC sound transmission behaves as linear systems and they both excite the basilar membrane in the cochlea similarly. The cancellation results are presented as the deviations from this hypothesis; except for a few larger deviations, the intrasubject deviations were generally less than 0.5 dB and 5°. The results from all three test categories indicate that the hypothesis of linear transmission systems and similarity of cochlear stimulation by AC and BC holds. However, due to the subjects' limited ability to conduct optimal cancellation and to imperfect methodology and equipment, the small deviations from perfectly linear cancellation that were observed do neither conclusively prove nor refute the possibility of small differences in the cochlear processing of AC and BC sound. Nonetheless, it is clear that if such differences in the processing of the two stimuli exist, they are small in magnitude.