抄録
Stimulation deafness is characterized by a h earing loss limited to high frequencies. The maximum threshold shift of hearing due to intense tone stim ulation has been considered to occur at a higher frequency than the stimulating tone. In 1934, RAWDON-SMITH found that temporary deafness due to intense tones often involved tones an octave above the fatiguing tone. 1) PERLMAN also reported that, when acoustic trauma was produced, the maximum dip was usually an octave above the frequency of the fatiguing tone2). RUEDI and FURRER described that the exposure of the human ear to a very intense pure tone produced an increase of the auditory threshold at frequencies above this tone3). DAVIS and others reported that the greatest loss of auditory sensitivity regularly occurred at a frequency about half an octave above the exposure tone, and often occurred throughout a range of one to two octaves above the exposure tone. 41
KAWATA studied the auditory fatigue caused by 1000 cps, 2000 cps, 3000 cps and 4000 cps pure tones of 110 dB in young subjects with normal hearing. He found that the maximum threshold shift for 1000 cps tone stimulation occurred at 1500 cps, for 2000 cps tone at 3000-4000 cps, for 3000 cps tone at 4000 cps and for 4000 cps tone at 6000 cps. In the combined chart of these curves, he pointed out that the intersection of each auditory fatigue curve (audiogram after stimulation) was found on the ordinate of 4000 cps. And, he indicated that only the auditory fatigue curve for the 3000 cps tone crossed this ordinate below that intersection point. He also found the same phenomenon in bone conduction test. From these results, he deduced that any intense pure tone, regardless of frequency, would cause hearing loss of approximately the same degree at the c5 area of the cochlea. 5) 6) HOOD7) and NAKAMURA8) reported that the maximum threshold shift occurred at approximately the same frequency with a stimulating tone of relatively low intensity and that the frequency of the maximum threshold shift moved upward with an increase of intensity of the stimulating tone.
BÉKÉSY studied the vibration pattern of the cochlear partition in the human cadaver using a stroboscope. He reported that high frequency vibration of the cochlear partition caused the greatest movement of the basilar membrane at the lower turn and the maximum movement moved to the upper turn as the frequency was decreased. 9) Utilizing a model experiment of the cochlea, NAKAMURA reported that as the intensity of vibration increased the movement of the basilar membrane toward the basal portion of the cochlea was more affected than that of the apical portion. But, the maximum movement of the basilar membrane due to vibration at a fixed frequency stayed at the same point regardless of the intensity of stimulation. 8) HILDING pursued the auditory physiology on the basis of anatomical studies with measurement of the human cochlear section. He reported that the directional conversion of hydrodynamic force produced the maximum impact point in the area around 6 - 8 mm from the basal end of the cochlea. 10) Using electrophysiological methods, TASAKI reported that low fr equency tones produced a significant cochlear potential at all regions of the cochlea while high frequency tones produced the potential at only the lower turn. 11)
Despite these many studies, the reason why the maximum threshold shift in hearing occurs at a higher frequency than the stimulating tone is not satisfactorily explained. The authors will discuss this problem from the standpoint of electrophysiological methods and findings in the cochlea
