Response of Cochlear Models to Aperiodic Signals and to Random Noises

Abstract

Traveling bulges along cochlear partition models were recorded in response to gradual step-function signals (the simplest form of a transient). Such a bulge resembles a train of waves decaying both in time and in space. Since each half-wave grows longer in duration with its rank order, it forms its own individual envelope, including the location of maximal displacement. The latter location depends upon the time constant in essentially the same manner as that in response to steady-state signals upon inverse frequency. The point of over-all maximal displacement (usually due to the first half-wave) varies with the time constant of the applied signal but also with the signal shape. At any given point along the partition, the propagation velocity of each half-wave varies with the initial amplitude and its inverse time constant while its deceleration with distance depends upon the inverse time constant only. This is signified by the fact that the velocity-distance curves of various portions of each bulge tend to approach a common point which is frequently located beyond the helicotrema. The response to random noise (and to bands thereof) is a superposition, in time and in space, of responses to single transients in random distribution.