Differential patterns of physiological masking in the anuran auditory nerve

Single fibers in eight nerve of anurans exhibit varying rates of short-term adaptation in response to long duration tonal stimuli. In this report, we show that the response of an anuran auditory nerve fiber to a short probe tone presented 10-1000 ms after a long duration adapting tone depends on the fiber's state of adaptation due to previous stimulation. These effects are most pronounced in fibers presumably originating from the amphibian papilla. Within this group of fibers, fast-adapting fibers, which are most sensitive to mid-frequency tones, showed greater response decrement than did slow-adapting fibers, which are most sensitive to low-frequency tones. Fibers tuned to higher frequency ranges, which presumably originate from the basilar papilla, showed response decrements similar to those shown by slow-adapting fibers from the amphibian papilla. These results indicate that anuran auditory nerve fibers, unlike mammalian auditory nerve fibers, are not homogeneous in their sensitivities to the effects of prior stimulation.