Peripheral basis of sound localization in anurans. Acoustic properties of the frog's ear.

Directional responses of single auditory fibers in the eighth nerve of northern leopard frogs (Rana pipiens) were studied in order to gain some insights into the acoustical properties of the frog's ear. In addition to the actual directional response of a fiber, a theoretical directional-response curve to the intensity-rate function of the unit. The difference in the two responses provided a measure of the directional characteristics of the frog's ear at the stimulating frequency which can be plotted in a polar diagram to show the directivity pattern of the frog's acoustic receiver. Directivity patterns were obtained from three groups of experimental animals under the following conditions: (I) mouth filled with moistened cotton; (II) contralateral ear coated with silicone rubber cement; (III) open mouth. Changes in the directivity patterns were observed with experimental manipulations and these were compared to those obtained from normal animals (Feng, A.S. (1980) J. Acoust. Soc. AM. 68, 1107-1114). The results suggest that the frog's ear behaves as a combination pressure-pressure gradient receiver.