1966 年 69 巻 3sup 号 p. 76-87
The author attempted to develop a new testing method to diagnose affected parts in perceptive deafness easily, quickly, and accurately in the course of daily clinic.
The author found, as a result, that the diagnosis affected parts is possible by combining three test methods, namely the conventional audiometry (air and bone-conduction threshold test), a threshold test using an interrupted tone and a continuaus tone which are self-recorded, and a threshold difference test based on the masking level difference phenomenon of pure tones.
This report describes the principles of diagnosis the scope of application of each test method.
1. The conventional audiometry; This method should be considered to be threshold test designed to screen perceptive deafness out of various hearing disturbances. It should be noted that this routine audiometry, when employed for screening purposes, in subject to the following three restrictions: 1) the limit of the out-put level of bone conduction, 2) cases where the measurement of bone conduction threshold is impossible, and 3) cases where some types of perceptiv deafness fail to be screened.
This problem can be solved by devising a test method which would enable screening of perceptive deafness without measuring bone conduction thresholds. As a method to suit this purpose, I have introduced - combination of an air conduction threshold test and an intensity difference limen using "superimposed pip" test developed by the author.
2. Diagnosis by self-recording method; This is a new testing method developed by the author and his collaborators with a view to classify perceptive deafness into inner ear disturbances and retro-cochlear disturbances.
In diagnosis, the author used the threshold difference between the threshold obtained by the interrupted tone (duration 200msec; rise and fall time 25msec ; repetition time 400 msec) ascending method and the threshold obtained through the continuous tone descending method (after exposing the ear to the level of 85dB on the hearing loss dial for thirty seconds). The case may be regarded as inner ear deafness, if this threshold difference is within 20dB, and as retro-cochlear deafness if the value is over 20dB.
3. Diagnosis by Masking Level Difference Test (MLD-Test, EBIHARA'S) ; This method is employed to classify retrocochlear disturbances into those located in peripheral region and those located in central region of the tertiary neuron in auditory passway.
This principle employs the difference in pure tone threshold caused when the sound images of a pure tone and of a noise are fused or separated artificially in binaural hearing. With the 1000cps, tone used for the MLD-Test, there is no distur. bance if this threshold difference is above 5dB, and if the value is under 4dB, the central region of the tertiary neurons in central auditory passway will be considered affected