The goal of the mammalian psychophysical research is to describe quantitatively the performance of chinchillas in auditory detection and discrimination tasks. These studies serve as an important conceptual bridge between the human psychophysical research and the neurophysiological studies in the chinchilla. Operant conditioning using positive reinforcement is used to train chinchillas to make a behavioral response to a sound. Animals press down on a response lever to initiate a trial; following a random holdtime, a test stimulus may or may not be played through the loudspeaker. In order to receive a food pellet reward, chinchillas are trained to release the lever when the test stimulus is played or to continue holding the lever down if the test stimulus is not played. The parameters of the test stimulus are varied, and behavioral responses are categorized in terms of hits, misses, false alarms and correct rejections. Psychometric functions are generated, and signal detection theory is used to analyze behavioral performance. Previous studies from this facility have shown that although chinchillas are generally less sensitive than human subjects, behavorial performance as a function of a given stimulus variable is similar between chinchillas and human listeners. These studies suggest that the underlying neural mechanisms that process the sound are fundamentally the same in chinchillas and human subjects. Test stimuli in current experiments include complex sounds that produce the perception of pitch in human listeners as well as sounds having temporal variations in amplitude. These stimuli are identical to those used in the human psychophysical studies at Parmly.