Multiple components in distortion product otoacoustic emissions from the amphibian ear

Abstract

Distortion product otoacoustic emissions (DPOAEs) are weak intermodulation distortions generated in the inner ear in response to two stimulus tones. Both the amphibian papilla and the basilar papilla in the inner of the frog may generate DPOAEs [Van Dijk and Manley, Hear. Res. 153, 14–22 (2001)]. Here, we measured the level and phase of DPOAEs in the Leopard frog, Rana pipiens, in response to stimulus tones between 40- and 90-dB SPL. Results show that for stimulus tones in the amphibian papilla frequency range, two components contribute to DPOAEs. One component dominates for stimulus levels below about 70-dB SPL, while the other is most prominent at higher levels. The transition between both components is accompanied by a conspicuous phase change, and sometimes by a notch in the amplitude response curve. Similar results were obtained in the basilar papilla frequency range, but in addition a third component was present for stimuli below about 55-dB SPL. With the exception of this third component, our findings are remarkably similar to those in mammals, despite the structural differences between the mammalian and amphibian inner ear. [Work supported by NWO.]