[Probe to the bone-conduction phenomenon].

OBJECTIVE: To probe into the rule of bone-conduction measurement by testing a group of health young students with normal hearing and groups of case with different diseased ears, in order to provide some instructions for clinical audiometry. METHOD: Subjects included 20 health young students with normal hearing, 113 cases with different hearing loss. We tested all the subjects Weber Test and bone-conduction threshold by masking. RESULT: Weber Test lateralization dependented on the difference of binanural sensitivity when binaural had no conductive impairment. Different conductive impairment improved bone-conduction response at different frequencies. When monaural had conductive impairment and the other ear normal, there were 3-5 octaves WT lateralizated to the diseased ear. When there were binaural conductive impairments, bone-conduction response dependented on the nature and degree of the impairment, WT lost the rule. CONCLUSION: In order to avoid the negative effects of central masking and overmasking, our observations came to the conclusion that some conditions as follow need no masking: (1) There are no conductive impairment binaural, and the air-conduction pure tone threshold (PTT) gap between binaural higer than 40 dB, when we test bone-conduction PTT of better ear, we need no masking, as for the poor ear, it's bone conduction will come cross to the contralateral ear. (2) When one ear normal and the other is the conductive impairment,need no masking when testing the diseased ear. (3) There are conductive impairments binaural, bone-conduction PTT is normal, and air-conduction PTT is higher than interaural attenuation, we cannt get a true bone-conduction PTT by masking, but can determine the type of hearing loss and estimate the integrity of the sensory-neural system by other audiometry measurements.