Frequency discrimination in noise: comparison of cat performances with auditory-nerve models.

Pure-tone frequency discrimination (delta F) performances were measured in cats and compared to neural models of these delta F performances based on auditory-nerve data in cats. Animal psychophysical techniques were used to train cats to discriminate frequency changes for pulsed pure tones in background noise at both 1.0 and 3.0 kHz. A go-left, go-right procedure was employed, and delta F's were measured in noise as a function of signal level at a constant signal-to-noise ratio. In contrast to human listeners, cats showed increases in delta F at 1.0 kHz with increasing signal level. Model estimates of delta F's based on rate responses in the cat auditory nerve predict increasing delta F with increasing signal level, the trend observed in the cat psychophysical data. Model estimates of delta F's based on temporal (phase-locking) properties in cat auditory nerve, on the other hand, predict decreases in delta F that have been observed in previous data from human listeners [Dye and Hafter, J. Acoust. Soc. Am. 67, 1746-1753 (1980)]. These results suggest that for cats, average rate, rather than phase-locking, may be used by the central nervous system in performing frequency discrimination in background noise at 1.0 kHz. At 3.0 kHz cats showed little change in delta F as a function of signal level, a result similar to the trend for human listeners to show no change or slight increases in delta F with increases in signal level for tones in the 2- to 3-kHz range.