Detection of sinusoidally amplitude modulated noise by the chinchilla

Amplitude modulation thresholds for sinusoidally amplitude modulated noise were obtained from four monaural chinchillas using shock-avoidance conditioning procedures. The noise was band limited at either 10 or 20 kHz, amplitude modulated at frequencies between 2 and 4096 Hz and presented at levels between 52 and 73 dB SPL. The modulation thresholds of the chinchilla were approximately 9% (— 20 dB) at modulation frequencies below 32 Hz. At higher modulation frequencies, thresholds increased at the rate of 1.9 dB/octave. Modulation thresholds were also measured in human listeners using the same experimental apparatus. Amplitude modulation functions for both subject groups exhibited low-pass characteristics; however, the thresholds for humans were better than those of the chinchilla at modulation frequencies below 64 Hz.