Tuning in the spatial dimension: evidence from a masked speech identification task.

Spatial release from masking was studied in a three-talker soundfield listening experiment. The target talker was presented at 0 degrees azimuth and the maskers were either colocated or symmetrically positioned around the target, with a different masker talker on each side. The symmetric placement greatly reduced any "better ear" listening advantage. When the maskers were separated from the target by +/-15 degrees , the average spatial release from masking was 8 dB. Wider separations increased the release to more than 12 dB. This large effect was eliminated when binaural cues and perceived spatial separation were degraded by covering one ear with an earplug and earmuff. Increasing reverberation in the room increased the target-to-masker ratio (TM) for the separated, but not colocated, conditions reducing the release from masking, although a significant advantage of spatial separation remained. Time reversing the masker speech improved performance in both the colocated and spatially separated cases but lowered TM the most for the colocated condition, also resulting in a reduction in the spatial release from masking. Overall, the spatial tuning observed appears to depend on the presence of interaural differences that improve the perceptual segregation of sources and facilitate the focus of attention at a point in space.