Tone-derived vs. tone-in-noise-derived filter functions of frog auditory nerve fibers: a comparison

Intracellular recordings were made from 112 auditory nerve fibers of Rana pipiens pipiens. For each fiber, we determined its frequency-threshold curve (FTC), and its threshold to CF-tones simultaneously masked by either cosinusoidal or inverted comb-filtered noise (CFN). From the difference between the masked thresholds using cosinusoidal and inverted CFN, the filter function of the auditory fiber was calculated based on a constant signal-to-noise algorithm (Pick, 1980). The calculated filter functions and FTCs were then compared. Of the 63 comparisons made, 42 were statistically indiscriminable, 15 fibers produced a calculated filter function that differed significantly in shape from the FTC, and six fibers produced a flat filter function. We conclude by evaluating our methods, especially for the experimental conditions found in the frog, and compare and contrast our results with those observed in mammalian systems.