Localization of Aural Harmonics along the Basilar Membrane of Guinea Pigs

Abstract

Harmonic distortion has been shown to originate hydrodynamically in cochlear models, its essential manifestation being Bekesy''s "eddies" and their sequelae. One of the major postulates derived from this study was that the distortion be resolved along the cochlear partition in accordance with the place principle of frequency localization. Experiments on guinea pigs were conducted in an effort to support this latter postulate. A method of recording cochlear microphonics by means of differential electrodes was chosen. This method had been previously used by Tasaki, Davis, and Legouix (J. Acoustical Soc. Amer., 24: 502. 1952) for mapping amplitude and phase alteration along the basilar membrane. The results of the present study indicate (1) that distortion within the cochlea occurs at a lower intensity level than it does in the middle ear (confirming results of earlier investigators), and (2) that each newly created harmonic forms a traveling-wave pattern of its own along the basilar membrane in accordance with the place principle. These results support the hydrodynamic hypothesis of the origin of intra-cochlear distortion.