Short-term and long-term effects on the masking level difference following middle ear surgery.

The masking-level difference (MLD) was measured in a group of adult listeners having unilateral otosclerosis before stapedectomy surgery, 1 month following surgery, and 1 year following surgery. The results indicated that the MLD in this group improved significantly over each of the sequential tests. In contrast, for a group of normal-hearing listeners, the MLD did not change significantly over sequential testing. The results support an interpretation that a period of exposure to abnormal binaural auditory input (as occurs in a unilateral conductive loss) can blunt sensitivity to binaural cues after normal binaural input has been restored in most adult listeners, however, there appears to be a relatively long-term readjustment or adaptation, such that the sensitivity to binaural cues recovers to a normal or near-normal level at the 1-year postsurgery retest. Two of eight listeners did not show recovery to a normal MLD value over this time period. The efficiency and rate of readjustment may differ among individuals.