Much of what is now known about hearing mechanisms in vertebrates has come from studies using behavioral and psychophysical techniques to ask questions regarding auditory detection and processing. These studies have included determination of detection capabilities for a variety of signals presented in a quiet environment and in the presence of other signals. Such studies are valuable in determining the resolving and analysis capabilities of the auditory system. Other investigations have been directed at determining an animal’s ability to discriminate between signals that differ in a variety of parameters, including intensity, frequency, spectral components, position in space, or temporal relationships. Such studies provide insight into detection capabilities of an animal, as well as provide information on mechanisms of acoustic processing at different levels of the auditory system.