Nonsense-syllable recognition in noise using monaural and binaural listening strategies

Using a binaurally equipped KEMAR manikin, syllables of the CUNY Nonsense Syllable Test were recorded in sound field at 0-degree azimuth against a background of cafeteria noise at 270-degrees azimuth, at several signal-to-noise (S/N) ratios. The combination of inputs recorded at each ear was delivered to ten normal-hearing (NH) and eight sensorineurally hearing impaired (HI) listeners through insert ear phones to produce five experimental listening conditions: (1) binaural head shadow (HS), in which ear presentation was analogous to the original stimulus recording, (2) binaural favorable (BF), in which the noise-shadowed (right-ear) recording was presented to both ears, (3) monaural favorable (MF), in which the noise-shadowed recording was presented only to the right ear, (4) monoaural unfavorable (MU), in which the noise-unshadowed (left ear) recording was presented only to the left ear, and (5) simulated monoaural aided (SMA), in which the noise-shadowed recording was presented to the right ear and the noise-unshadowed recording--attenuated by 20 dB relative to the HS condition--was presented to the left ear. All main effects (subject type, listening condition, and S/N ratio) were statistically significant. Normal listeners showed 3.3- and 3.2-dB advantages, respectively, due to head-shadow and binaural squelch, over hearing-impaired listeners. Some hearing-impaired listeners performed better under the SMA or BF conditions than under the HS condition. Potential digital signal processing strategies designed to optimize speech understanding under binaurally aided listening conditions are discussed.