DPOAE two-source separation in adult Japanese quail (Coturnix coturnix japonica)

The current study is the first to deconstruct the DPOAE into separate nonlinear and reflection source components in birds. We examined the isolated DPOAE generator components in 22 normal, adult Japanese quail using an IFFT analysis to quantify the resultant phase and component contributions to the distortion response as a function of input level. Fine structure (FS) analysis across a F2 range of 500-6,000Hz at 60dB SPL (L1=L 2) showed that approximately half of the quail displayed FS amplitude patterns highly influenced by the presence of multiple internal reflections while half showed relatively little amplitude variance with less interference by additional reflections. Similar to mammals, DPOAE phase patterns were independent of intensity with the nonlinear component frequency-independent and the reflection component frequency-dependent. At high input levels, the nonlinear component amplitude proved dominant over the reflection component, but at low input levels component amplitudes were similar. Our results imply that there is a common underlying physiological mechanism driving the DPOAE in the avian and mammalian inner ear and suggests that two component DPOAE analyses may be a sensitive tool for the evaluation of stereocilia resonance contributions to underlying nonlinear properties of the inner ear across species.