Masker interaural phase and the MLD: effects of conductive hearing loss.

Sensitivity to binaural signals that were interaurally antiphasic with respect to the masking noise was examined as a function of the interaural phase of the masking noise, for listeners with normal hearing, and listeners with conductive hearing losses. Some of the hearing-impaired listeners were tested both before and after middle ear surgery. In agreement with previous findings, the normal-hearing listeners showed the lowest thresholds when the masking noise had no interaural phase shift, with thresholds increasing monotonically as the interaural phase of the center frequency of the masker approached +/- 180 degrees. Although many of the masked threshold functions of the hearing-impaired listeners showed significant changes in thresholds as a function of masker interaural phase, most of the functions were abnormal in shape, and few showed peaks for the interaural masker phase of 0 degrees. Although functions often continued to be abnormal after middle ear surgery, a few subjects obtained postsurgery functions that were correlated with the average normal function. The results indicate that although normal-hearing listeners generally have the lowest antiphasic signal threshold for a masker with 0 degrees interaural phase, conductively-impaired listeners often do not show a clear minimum for antiphasic signal threshold at any particular masker interaural phase.