The Bases of Difficulties in Spatial Hearing for Speech: Investigations using Psychoacoustic Techniques and Magneto-encephalography

The experiments reported in this thesis investigated the bases of the difficulties that older adults report when trying to listen to what one person is saying when many other people are speaking at the same time. Experiments 1–4 examined the roles of voluntary and involuntary attention in a spatial listening task for speech among young normally-hearing listeners. When talkers started speaking one at a time, listeners could hear out a target phrase that was less intense than overlapping masker phrases. When talkers started speaking in pairs, listeners could attend to a less intense target phrase only when told in advance who to listen for, where they would speak from, or when they would speak. The distracting effect of the onset of a competing talker was effective over a broad time window. Experiment 5 investigated the relationships between performance on the spatial listening task and several predictors of performance among young and older normally-hearing adults. Poorer performance was related to self-reported difficulties with listening in everyday situations, poorer hearing sensitivity, and poorer performance on visual and auditory tasks of attention requiring fast speed of processing. Experiment 6 examined brain activity associated with successful performance on the spatial listening task using magneto-encephalography. Differences in cortical activity were identified at moments when attention had to be sustained on the target phrase, or when listeners had to resist distraction from the onset of a new masker phrase. Amplitudes, and/or latencies, of differences in brain activity arising in regions associated with attentional processes were related to performance. The results suggest that skills in attention contribute to the ability to listen successfully in multi-talker environments. Age-related difficulties with listening in those environments may arise due to a specific reduction in the ability to resist distraction or a general reduction in the speed at which information can be processed.