NEW HEARING TEST ABOVE THRESHOLD AND ITS CLINICAL SIGNIFICANCE

Abstract

Hearing test above the threshold has been experimented in various ways for differential diagnosis for so-called perceptive deafness. However, all the methods experimented so far have certain advantages as well as disadvantages. Therefore, a new method was experimented in the test above the threshold of hearing on one ear, clarifying the significance and fundamentals of the test. Method of the test:1. The hearing-loss curve was prepared.2. A sound of 20db. above the threshold was applied to a subject, the loudness being kept in his mind.3. A point was seeked where the sound of the same frequency reached the same loudness of the sound mentioned in 2 above by increasing the former from 0db.4. A point was seeked where the sound of the same frequency reached the same loudness of the sound mentioned in 2 above by decreasing the former from 90db.It was found, then, that some difference between the first point and the second point appeared for sounds of various frequencies. The distance between these points was taken as the result, Although modulations were carried out not only at 20db. above threshold but also at 40 db. and 60db above threshold, the results obtained at 20db. above threshold will be mainly explained in the following.Results of the test:The difference between the two points (hereafter referred to as the range of sensibility) was about 8 to 15db. for those whose hearing organ was ordinary as well as fot those of conduction deafness, while it was different for those of perceptive deafness. For instance, in Meniere's disease, the range was naraower. In central deafness, the range was wider. Most cases having positive recruitment phenomenon showed narrower range. These results indicated that the test had certain relations to the recruitment phenomenon.Following that indication, the test was experimented on animals with lesions of Corti's organs by giving a sound of various intensity to them only to ascertain the occurrence of recruitment phenomenon. Furthermore, in parallel to the test that sound stimulation caused the shift in the threshold of those with normal hearing ability, it was found that the range of sensibility of those with normal hearing ability got narrower after immediately after sound stimulation as the tone of sound became higher. The fact seemed to indicate that the test could be applied to ascertain a lesion in Corti's organ and the existence of recruitment.From the results mentioned above, it can be assumed that:(1) Cases showing narrower ranges indicate a lesion in Corti's orgarn.(2) Cases showing normal ranges have either a lesion in acoustic nerve, in variation of labyrinthine fluid, or lesions both in the acoustic center and. Corti's orgarn.(3) Cases showing wider ranges have lesions in the acoustic center.(4) This test above threshold is canbe applied to one ear in order to diagnosis of possible localization of lesions in percetive deafness.