The Perception of Repeated Bursts of Noise

Abstract

Noise interrupted at a steady rate has essentially the same spectrum over the range of frequencies transduced by the ear-phone as does continuous noise. The frequency corresponding to the rate of interruption is not intensified in the spectrum. Consequently, the ability of listeners to respond differentially to the rate of interruption cannot be explained on the basis of a simple resonance theory of hearing. The point at which an interrupted noise becomes indistinguishable from a continuous noise depends on the rate of interruption, the sound-time fraction, and the intensity of the noise. For a sound-time fraction of 0.5, the presence of interruptions can be detected at rates well above 1000 per sec. Differential sensitivity to changes in the rate of interruption (with a sound-time fraction of 0.5) is poor above 250 interruptions per sec. Also at these high rates the listener loses his ability to match the frequency of a pure tone to the rate of interruption. Presumably the ability to perceive interruptions in a random noise depends upon the synchronous firing of the fibers in the auditory nerve. This hypothesis is supported by the correspondence between auditory sensitiveity to changes in the rate of interruption of a noise and the tactual sensitivity to changes in the frequency of a vibrating pressure applied to the skin.