Compressional Bone Conduction in Cochlear Models

Abstract

Animal experiments have suggested the possibility that the compressional mode of bone conduction might produce a displacement of the cochlear partition, even when the cochlear windows and all other potential pressure outlets are closed. This assumption was found correct for the case of a cochlear model. It executed so-called "distortional" vibrations, i.e., while its walls in one place moved inward, those in the other moved outward and vice versa. This mode of motion tends to keep constant the total volume of the enclosed incompressible fluids. The two perilymphatic spaces are known to differ in volume. Distortional motion causes the volume difference to alternate, thus producing compensatory displacements of the partition. This is in contrast with the effect upon the partition of the translatory and antiphasic movements of the cochlear windows in response to air-conducted sound. When both windows are open, or only one is occluded, the displacement of the partition, due to bone-conducted sound, represents the combined results of distortional and translatory motion. The generation of traveling waves, when input and output are distributed over the entire cochlear shell, as in boae conduction, is discussed in terms of general cochlear mechanics.