Binaural Intelligibility level Differences in Normal and Hearing-Impaired Individuals

Introduction Release from masking, or the masking level difference (MLD), is a phenomenon in which the binaural auditory system can take advantage of interaural phase differences to improve the detection of signals in a background of noise. The MLDphenomenon can be observed for both tonal and speech signals at or near threshold levels. Similarly, intelligibility of speech presented at suprathreshold levels can be improved by manipulating interaural phase angles of the signal or the background noise. The improvement of supra threshold speech intelligibility has been referred to as the binaural intelligibility level difference (BILD) (Levitt & Rabiner, 1967). Although numerous studies have investigated MLDs for speech and pure tones (e.g., Gerber, Jaffe, & Alford, 1971), relatively little research has been directed toward the investigation of BILDs. Furthermore, investigation of release from masking has dealt primarily with young normal-hearing populations (Gerber, 1972). No evidence has been presented thus far to determine how the hearingimpaired elderly perform release-from-masking tasks at suprathreshold levels, that is, how they are affected by the BILD phenomenon.