Coding of signals in noise by amphibian auditory nerve fibers.

Rate-level (R-L) functions derived for pure-tones and pure-tones in broadband noise were obtained for auditory nerve fibers in the treefrog, Eleutherodactylus coqui. Normalized R-L functions for low-frequency, low-threshold fibers exhibit a horizontal rightward shift in the presence of broadband background noise. The magnitude of this shift is directly proportional to the noise spectrum level, and inversely proportional to the fiber's threshold. R-L functions for mid- and high-frequency fibers also show a horizontal shift, but to a lesser degree, consistent with their elevated thresholds relative to the low-frequency fibers. The implications of these findings for the processing of biologically significant sounds in the high levels of background noise in the animal's natural habitat are considered.