In normal cochleas of cats and chinchillas, nonlinear interactions between the primary components of two-tone stimuli lead to the generation and propagation of distortion products (f2-f1) and (2f1-f2) and to two-tone suppression as we have observed in responses of populations of cochlear nerve fibers. Spatial patterns of two-tone suppression show that the f1 response component is suppressed around the f2 place by the simultaneous presence of the f2 response component, and vice versa. Spatiotemporal characteristics of each of the distortion products (f2-f1) and (2f1-f2) in responses of cochlear nerve fibers are quite similar to those of the responses to a single-tone stimulus with frequency equal to the distortion frequency in fibers innervating regions near and apical to the distortion-frequency place. Such a similarity strongly supports the conclusion that the distortion products are mechanically propagated along the basilar membrane in the same manner as the travelling-wave response to externally-applied single-tone stimuli. Models for basilar-membrane motion with nonlinear damping (Kim, Molnar and Pfeiffer, 1973; Hall, 1974, 1977; Matthews, 1977) exhibit propagated distortion products and two-tone suppression phenomena which are qualitatively similar to these experimental observations. These similarities suggest that these nonlinear phenomena in cochlear responses to two-tone stimuli may result from a common mechanism that produces nonlinear damping of basilar-membrane motion. Our data show that the propagated distortion products (f2-f1) and (2f1-f2) are affected by alterations of the organ of Corti in the region of primary-frequency places. This supports the conclusion that the propagated distortion products are generated in the cochlear region of the primary-frequency places and suggests that the nonlinear mechanism which generates them is physiologically vulnerable and that the functional state of the organ of Corti may significantly affect basilar-membrane motion.
|Original language||English (US)|
|Number of pages||19|
|Issue number||Suppl. 9|
|State||Published - Jan 1 1979|
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