Understanding speech in complex acoustic environments: the role of informational masking and auditory distance perception

One of the greatest challenges for the auditory system is communicating in environments where speech is degraded by multiple spatially distributed maskers and room reverberation. This "cocktail-party" situation and the related auditory mechanisms have been a topic for numerous studies. This thesis primarily investigated speech intelligibility in such environments— specifically considering the role of differences in distance between talkers and the contribution of informational masking (IM). The first two studies investigated the role of differences in distance between competing talkers on spatial release from masking (SRM) in normal hearing (NH) and subsequently, hearing impaired (HI) listeners. Intelligibility improved for both NH and HI listeners when moving the masker further away from the target. Contrastingly, when the target was moved further away and the maskers were kept near the listener, the results varied significantly across subjects. While intelligibility improved for some NH listeners, the HI listeners performed substantially worse. It was hypothesized that in this condition IM was caused by masker distraction rather than confusion. In the third study, the role of IM was investigated in a simulated cafeteria environment. Substantial IM effects were only observed when the target and masking talker were colocated and the same person. In conditions that resemble real life, no significant IM effects were found. This suggests that IM is of low relevance in real-life listening and is exaggerated by target-masker similarities and the colocated spatial configuration often used in previous listening tests. The final study investigated the effect of nearby masking talkers in a simulated cafeteria environment with NH and HI listeners. The study demonstrated that for realistic conditions, nearby distracters introduce a significant amount of IM in both NH and HI subjects. However, the observed IM was likely not due to target-masker confusions, but rather caused by the nearby masker distracting the listener. Overall, this work suggests that (i) NH and HI listeners use distance related cues in the cocktail-party environment, (ii) in such environments IM related to target-masker confusions is of little relevance, and (iii) nearby maskers introduce IM - likely due to distraction of attention. These findings contribute to our understanding of auditory processing and could potentially have implications on signal processing methods for hearing devices.