The Effect of Sensation Level upon Pitch Discrimination in a Continuous Thermal Noise Mask

Abstract

The intensity of a thermal noise was adjusted until it just masked a 1000∼ tone of 40-db sensation level. The pure tone was then increased either 3, 5, 7, 10, or 15 db in intensity, and differential pitch threshold obtained by the method of constant stimuli. The same procedure was followed for 1000∼ tones of 30, 20, and 10-db sensation level. For each sensation level a plot was drawn relating the differential threshold to the intensity of the pure tone above its detection threshold in the mask. For the lower sensation levels, sensitivity was relatively worse as a function of pure tone intensity above the mask. Control tests with no mask were run to determine whether this effect was the result of the relation of tone to mask or simply to the poorer sensitivity found with lower sensation levels in quiet. It was concluded that the effect was largely caused by the tone-mask intensity ratio. A previous experiment had suggested that pitch discrimination was under certain masking conditions a function of log loudness, in sones. The present experiment indicates that at the lower sensation levels, discriminability may change even more rapidly as a function of loudness. Within the limits of this experiment a gradual transition occurs in the discriminability-loudness relationship.