The multiple contributions of interaural differences to improved speech intelligibility in multitalker scenarios.

Spatial separation of talkers is known to improve speech intelligibility in a multitalker scenario. A contribution of binaural unmasking, in addition to a better-ear effect, is usually considered to account for this advantage. Binaural unmasking is assumed to result from the spectro-temporally simultaneous presence of target and masker energy with different interaural properties. However, in the case of speech targets and speech interference, the spectro-temporal signal-to-noise ratio (SNR) fluctuates strongly, resulting in audible and localizable glimpses of target speech even at adverse global SNRs. The disparate interaural properties of target and masker may thus lead to improved segregation without requiring simultaneity. This study addresses the binaural contribution to spatial release from masking due to simultaneous disparities in interaural cues between target and interferers. For that purpose stimuli were designed that lacked simultaneously occurring disparities, but yielded a percept of spatially separated speech nearly indistinguishable from that of non-modified stimuli. A phoneme recognition experiment with either three collocated or spatially separated talkers showed a substantial spatial release from masking for the modified stimuli. The results suggest that binaural unmasking made a minor contribution to spatial release from masking, and that rather the interaural cues mediated by dominant speech components were essential.