Reverse Transfer Function Research Articles

Ear-canal cochlear otoacoustic emission acoustic distortion products (DPs) appear to provide a window into outer hair cell function and are becoming an important noninvasive cochlear evaluation research tool. If they are to become clinically useful, a better understanding of their production and measurement is needed. The magnitude of the DP depends on the acoustic load of the transducer as well as the cochlear input impedance. The ear-canal impedance and the ER-2 and ER-10B acoustic impedance have been measured and predictions of the reverse transfer function were made. Less well understood are observed standing waves in the ear canal at high frequencies. These may be controlled by insertion of the sound delivery tubes deep into the canal. Measurement of the DPs using an Ariel DSP-16 signal processing board is described in a portable PC-notebook configuration. DPs are approximately related to hearing level (HL) according to the formula DP=8−0.5 HL, where both DP and HL are in dB. Several different useful measurement paradigms that have been investigated will be described.