DL testの検討—変調法及び二音比較法

　I．緒言

　現在日常の臨床に振幅変調によるDL testがよく用いられている。然しこのTestはFowlerのalternate binaural loudness balance testとは違つた意味を持つている。即ち振幅変調は音の強さの連続的変化による検査で，強さの異る2つの音を比較して，二音の強さの差を検査することとはことなつている。従つてこの検査の相違は結局，音が連続的に変化するか，断続的に変化するかにある。今迄DL testは色々と工夫され，多くの変法が出来たが，連続的に変化する音を用いるという点では変らないので，Balance testと違つた結果が出るのは当然とも云える。然し現状ではDL testの成績をBalance testと同じとみなし，誤つた結論を下すことも起り得る。そこでDL testとBalance testの相違について一応の検討が必要なわけである。一方市販のオージオメータはDL測定装置が統一されておらず，時に複雑な装置のものもあり，検者をまどわすばかりか，経済的にも無駄が多い。そこでDL testの中で如何なる変調法がBalance testに近い結果となるか検討するとともに，Balance testと原理的に同じと考えられる二音比較法によるrecruitment測定法を検討し，これが変調DL測定法とどのように異るかしらべてみたところ新しい知見を得たので報告する。

The DL test was carried out in normal persons by amplitude modulation. The pure tone was modulated as follows: the one by square and the other by sine wave, the mo-dulated frequency maintained at 6,3, and 0.5 c/s. In the results of these test no remarkable difference was observed.

In modulated tone tests persons tested discriminated beats. The discrimination of beats seemed to be easier at 30 db above threshold than at 10, and furthermore persons affected with nerve deafness better than those who were normal.

The modulated DL test was carried out in 6 cases who showed recruitment pheromenon by binaural loudness balance test. The DL was found to be normal in 2 of these cases.

The value of DL discrimination in normal ears proved to be greater in two-tone com-parison test than that obtained by modulated DL test: this value when expressed in terms of dB became larger proportionally to the increase in the intensity of test tones, while the same value under modulated test became inversely proportional, i. e., the greater the tone the smaller the value.

There appeared to be a general tendency that the DL value obtained by two-tone comparison test to be smaller in persons with nerve deafness than in whom the hearing were normal.