This book reviews recent research on the ability of human listeners to discern changes in the shape of complex acoustic spectra--what is known as auditory profile analysis. It also discusses in a systematic way issues surrounding the discrimination of a change in acoustic intensity and the physiological mechanisms responsible for these discrimination processes. The author concludes with two new theories that provide a way of understanding more complex auditory skills, such as those involved in listening to music and speech. This book will be of interest to psychoacousticians, psychophysicists, physiological psychologists, and experimental psychologists.