Binaural hearing after middle ear surgery. Masking-level difference for interaural time and amplitude cues.

Previous investigations have shown that binaural hearing is often abnormal in patients having conductive hearing losses, and even in patients who have had hearing thresholds corrected by middle ear surgery. The present study assessed further the masking-level difference (MLD) in patients who had previously undergone middle ear surgery. The stimuli were chosen such that the sensitivity to interaural time difference cues and to interaural amplitude difference cues could be assessed independently. Results indicated that the MLD is abnormal in more than a third of 15 patients, even after surgery has restored normal hearing at the frequency of the test. The MLD is more likely to be reduced for the cue of interaural time difference than for interaural amplitude difference. Subjects who had lesions of long duration, early onset, and large asymmetry were particularly likely to have reduced MLDs.