Two-tone forward masking patterns and tinnitus.

Forward masking is the masking of a signal by a preceding masker. For normal observers, if two tones are employed as the forward masker, the addition of the second tone (which increases the masker energy) may make the signal easier to hear. This decrease in the masking effect (or unmasking) has been interpreted as evidence for lateral suppression in hearing. For five subjects with tinnitus, all of whom have a sensorineural loss caused by noise trauma or noise exposure, there is no unmasking for (at least) one signal frequency in the region of the tinnitus. However, unmasking does occur for (at least) one signal frequency in the region without tinnitus. The frequency region of the tinnitus is inferred from pitch matches and from determination of the frequency region of the noise needed to mask it. For comparison, data from three normal subjects also are included. For the subjects with tinnitus, two-tone forward masking patterns are decidedly different in the normal and the tinnitus regions.