Distortion product otoacoustic emissions in the tree frog Hyla cinerea

The frog inner ear contains two hearing organs: the amphibian and the basilar papilla. The amphibian papilla is sensitive to low- and mid-frequency stimuli (0.1-0.5 and 0.5-1.3 kHz, respectively, in Hyla cinerea), while the basilar papilla is sensitive to high-frequency stimuli (2.8-3.9 kHz in H. cinerea). Distortion product otoacoustic emissions (DPOAE) were recorded from the ear of the tree frog H. cinerea. In each of six ears investigated, a cubic distortion product (DP) at 2f₁-f₂ was present when the primary frequencies f₁ and f₂ and the DP frequency were close to either the mid- or the high-frequency range. At frequencies between the sensitive ranges of both papillae, no emissions were observed. For the basilar papilla, the dependence of DP level on the primary tone frequency ratio f₂/f₁ showed a pattern characteristic of the response of a single nonlinear resonator. Thus, in agreement with neural data, DPOAE from the basilar papilla reflect the contribution of a single auditory filter to emission generation.