Directional characteristics of the acoustic receiver of the leopard frog (Rana pipiens): a study of eighth nerve auditory responses.

The directional characteristics of the peripheral auditory system were assessed from studying the effects of sound direction on the responses of single auditory fibers in the eighth nerve of leopard frogs (Rana pipiens). Two types of directional response characteristics were observed which are correlated with the best excitatory frequency of the afferent fiber. Low-frequency sensitive neurons possessed V-shaped directional-response curves with a null at the frontal sound field. High-frequency sensitive neurons, on the other hand, showed a strong response to sound coming from the ipsilateral field with a progressively weaker response as the sound source was rotated to the frontal and contralateral field. Two directional cues were revealed: pressure variation at the eardrum and the directionality of the acoustic receiver system. The relative weight contributed by each factor also varies with frequency.