The study of specific responses that take place in the ear or in the associated central (neural) auditory pathways. The ear is the receptor organ of mechanoacoustic energy, which occurs in the form of sound pressure waves. The responses are elicited by appropriate stimuli of well-defined parameters presented at any level of the auditory system. Such responses may be registered with the aid of various, usually invasive, recording techniques which make use of mechanical, electrical, optical, radiological, or biochemical phenomena, or their combinations. The approach employed by physiological acoustics therefore is purely analytical. This is in contrast to the noninvasive, holistic approach employed by psychoacoustics, which lends itself well to experiments on human subjects. Systematic physiological experiments can be performed only in animals.