The Perception of Short Bursts of Noise

Abstract

Short bursts of random noise were used to study the perceptual growth and decay of the noise experience. Noise, unlike sinusoidal tones, does not change materially in spectrum as the duration of the sound is varied. A short burst of noise must be more intense in order to be equal in effectiveness to a longer noise. Thus the threshold of hearing is lowered by increasing the duration of the noise up to durations at least as long as 1 sec. The loudness of an intense noise, however, depends upon its duration up to durations of only 65 msec. Judgments of the slowest rate of decay of a noise which sounded indistinguishable from an abrupt termination also led to the concept of a critical time of approximately 65 msec. for the sensation to decay to threshold from any steady magnitude of stimulation. From these data it is inferred that the auditory system acts as if the growth and decay periods of the noise perception depend upon differences in latencies among the various neural paths in transmitting the cochlear activity to the higher centers in the brain. According to this hypothesis, the activity in the slowest pathways arrives at the higher center 65 msec. after the activity of the fastest pathways. By means of this hypothesis it was possible to predict the judgments of time of termination of noises in the two ears when the intensity of the noise differed between the ears.