Place mechanism underlying frequency analysis in the toad's inner ear

Abstract

The inner ear of toads has two distinct auditory organs. One of these, the amphibian papilla, gives rise to fibers which have a distribution of best excitatory frequencies (BEF's) while the fibers from the other organ, the basilar papilla, all have very similar BEF's. We recorded responses from single fibers from each of these organs in response to paired clicks in which in the interclick interval was varied systematically. Each fiber showed a firing probability which varied cyclically with interclick interval, indicating that the system impluse response within each organ is a damped oscillation. Furthermore the period of the firing probability curve of each fiber was equal to the reciprocal of its BEF. These results demonstrate that in the amphibian papilla frequency analysis is based on a place mechanism whereas the basilar papilla is a simply tuned resonant structure. [Supported by NIH.]