Spatial release from masking in listeners with asymmetric hearing thresholds

Abstract

Spatial release from masking was evaluated as a function of target-masker spatial separation in listeners with normal hearing and with chronic asymmetric hearing loss. The target was one of 20 vocoded words spoken by a female talker. The masker was a stream of vocoded nonsense sentences spoken by two other female talkers. Subjects listened in an anechoic chamber with loudspeakers at 1.9 m distance. The target was always presented from directly in front while the masker was presented from the front or from left or right at varying angular separations. In some conditions a copy of the masker with a delay of 4 ms was introduced at the front loudspeaker, simulating a reflection. Subjects detected the target in an adaptive 4AFC task. Results showed strong indications of informational masking in the co-located condition and spatial release that increased with masker angular separation, reaching almost 27 dB at wide separations in normal hearing listeners, and 22 dB even with the reflection. Listeners with asymmetric thresholds showed high across-listener variability in the spatial conditions but often smaller and strongly asymmetric release, presumably due to head shadow. The reflection reduced this head shadow advantage, and in one subject almost completely obliterated spatial release.