Auditory temporal processing & speech understanding

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My research has shown that reductions in the quality of sound input to the auditory system can reduce cognitive performance on measures of working memory and spoken language comprehension. These reductions are observed even when sounds are correctly identified. The timing properties of sound include fast changes in the fine structure of sound, as well as slow changes in the sound envelope. These changes in sound provide distinct cues required for understanding spoken language. My experiments have demonstrated that some older adults have problems using both fast and slow timing cues. The first goal of the proposed research will be to examine the inter-relationships between these different types of timing cues using non-speech and speech stimuli. Older adults with relatively good hearing have been interesting to study because their problems using sound timing cues may explain why they have trouble listening in noisy situations. However, similar results have been found when younger adults with normal hearing perform in conditions that simulate the auditory temporal processing problems of older adults. Because cognitive processing is reduced when the quality of the signal is reduced, even when it is still possible for listeners to accurately recognize words, the second goal of the research plan is to examine the time course of auditory/speech processing using on-line behavioural and physiological measures such as the measurement of brain responses so that the time course of listening can be measured. The third goal of the proposed research will be to model the temporal limits on the connections between the bottom-up (ear to brain) and the top-down (brain to ear) aspects of listening, especially in realistic, challenging listening conditions. For example, the speed of processing varies with the quality of the signal and the supportiveness of the context (e.g., sentence context for a word), but at some limit comprehension fails and the nature of such limits is not known. This topic is of great interest to engineers designing communication devices (e.g., hearing aids), as well as being of interest to psychologists, linguists and others who wish to understand how humans use sensory information during communication.