振幅変調脈音による聴覚異常順応現象

抄録

The present study was designed to elucidate the clinically significant four phenomena : threshold tone decay (TTD), temporary threshold shift in Bekesy fixed-frequency audiomety (TTS), wide separation between continuous and interrupted test signal tracings in Bekesy fixed-frequency audiometry, and reduced peak-to-peak amplitude of the Bekesy tracings. An amplitude modulated tone was introduced as a test signal in both the Bekesy audiometry and the self-recording TTD test, and comparisons between the continuous and interrupted tracings were made., The magnitude of amplitude fluctuation in the amplitude modulated tone was variable from 1db to 4db to in 1-db steps.
The results and conclusions were as follows :
(1) Both Bekesy and the TTD tracings were obtained with amplitude modulated tones for subjccts who showed marked TTD and TTS pheno mena for non-modulated pure tones. All the sublects showed gradual diminution in TTS and TTD with an increase in amplitude modulation of the test tones from 1db to 4db.
(2) Wide separation of the Bekesy tracings for a continuous tone and an interrupted tone was decreased with an increase in amplitude modulation of the test tone.
(3) For subjects who showed reduced peaktopeak amplitudes (less than 2.5), the reduced amplitude in their continuous tone tracings were increased and came to approximatel the amplitudes of the interrupted tracings in accordance with an increase in amplitude modulation of the test tones,
(4) Increase in amplitude modulation from 1db to 4db could seemly mask all fcur pathological phenomena. The degree of auditory adaptation at threshold levels can be seen to vary with the extent in db of amplitude modulation. The patterns of the amplitude modulated tracinge showed transitions between the most marked abnomal adaptation to the continuous tones and the normal (non-adaptation) findings to the linterrupted tones, according to the extent of db in the modulation.