Physiological Acoustics

a branch of acoustics that studies the structure and function of the sound-detecting and sound-forming organs of man and animals.

The methods of investigation used in physiological acoustics may be physical or psychophysiological. Physical methods are used in the instrumental analysis of sounds of biological origin and in the study of conduction of sounds from the environment to the receptor cells (for example, through the external and middle ear and then to the organ of Corti of the internal ear in terrestrial mammals) or from the sound-emitting organs to the surroundings (for example, from the larynx through the mouth into the air). Psychophysiological methods include the investigation of the response of man and animals to sounds and the recording of the corresponding bioelectrical potentials.

The study of a subject’s motor reactions as perceived by him (such study may make use of a verbal account by the subject) reveals the integral properties of human hearing and makes it possible to measure the differential absolute thresholds of hearing, to evaluate the subjective qualities of sound (such as loudness, pitch, and timbre), and to estimate man’s capacity for detecting (against background noise) and recognizing different acoustic signals. Of considerable importance is the investigation of conditioned reflex reactions to sound—for example, changes in the rates of respiration and pulse and in the electrical potential of the skin. Such investigation makes it possible to measure hearing thresholds and to determine the capacity of man and animals to detect and identify acoustic signals by their physical characteristics, such as intensity, spectral structure, and temporal structure.

The investigation of bioelectrical potentials reveals the capacity of individual auditory neurons and of the aggregates of neurons to process the information contained in acoustic signals—that is, the capacity to recode the parameters of sound waves into a sequence of nerve impulses, to identify characteristic recognition features of sounds, and to compare a given acoustic image with a standard stored in the memory. One of the major tasks of physiological acoustics is to ascertain the relationship between the responses of neurons and of the auditory system as a whole.

Physical analysis of the structure and function of the sound-emitting organs in man is important for solving problems of speech synthesis, for constructing devices facilitating communication between man and machine, and for developing automatic speech-recognition devices. The investigation of the sound-emitting structures in animals is essential for understanding the acoustic principles of echolocation, orientation, and communication in the animal world. In addition to studying the organs of sound reception and emission directly, physiological acoustics makes extensive use of mechanical, electrical, and mathematical modeling.