Studies on the generation mechanism of non-biological response in distortion product OTO-acoustic emission

We investigated the effect of non-biological artifacts on the measurement of distortion product oto-acoustic emission (DPOAE) using guinea pigs, and the generation mechanism of this phenomenon is discussed in the present paper. When a sound pressure of a stimulating tone was too large, an overtone was produced within the acoustic probe. When the difference in sound pressure between f1 and f2 was too large, artifacts appeared at frequencies of 2f1-f2 or 2f2-f1. Similar responses were generated when f1 and f2 were identical in sound pressure but exceeded a certain critical level. These non-biological responses could be easily differentiated from biological responses by subjecting the animal to anoxia. The input-output curve of DPOAE was biphasic and clearly showed this critical level in each animal. The results obtained in the present study suggest that the levels of f1 and f2 should be almost equal and should not exceed the observed critical level when measuring DPOAE.