Current progress in the programming and customization of assistive listening devices is limited due to an inadequate understanding of the context-dependent weighting of acoustic cues, the interference of these cues under adverse listening conditions, and the processing limitations imposed on these cues by aging and hearing impairment. This proposal targets this gap by identifying how older normal-hearing and hearing-impaired listeners use auditory cues during aided presentations for understanding speech in noise. The primary objectives of this project are to identify (1) the auditory cues that maximize speech understanding under adverse listening conditions, (2) how older listeners perceptually weight those cues, and (3) what auditory properties of the masking speech limit speech understanding the most. The central aim is to examine and identify the most informative auditory cues when only partial speech information is available in noisy environments for older listeners when audibility is restored. The central hypothesis is that in quiet, temporal envelope cues contribute most to speech intelligibility and are available for older listeners with aided hearing. However, in noise and competing speech the contribution of these acoustic cues are more limited, with the contribution of other cues becoming more important, such as the temporal fine structure, the processing of which may be limited by age or cochlear pathology.
Specific Aim #1 addresses speech in continuous, interrupting, and speech-babble noise. Different listener groups enable the investigation of age, cochlear pathology, and amplification contributions to auditory perceptual weights. Correlational analysis will explore the relationship between perceptual weights, speech in noise performance, and cognitive abilities.
Specific Aim #2 investigates temporal properties of the target and competing speech and how they interact. These experiments explore how temporal properties of the target talker facilitate speech understanding and properties of the competing talker interfere. Informational masking is also explored via time-reversed competition. The long-term goal of this project is to define acoustic parameters for enhanced programming of assistive hearing technology and identify individual weighting strategies to assist in future customization of these devices to capitalize on existing capabilities of the device and the listener. The significant contribution of this project is in identifying the speech cues that will be most informative for these listeners in different noisy conditions. The approach of this project is innovative. It uses novel signal processing strategies to independently vary complex temporal properties of speech via noisy signal extraction. Furthermore, it extends the 'glimpsing'theory of automatic speech recognition to the human understanding of speech from partial information. These innovations allow for the direct investigation of auditory temporal cue use during a competing talker paradigm, quite arguably the most difficult listening condition for older listeners.
The proposed research is relevant to public health because it identifies how older listeners use specific acoustic properties and defines the limit to which those properties are available to contribute to speech understanding during competing speech contexts. This research step is essential in the design of more cost effective hearing devices that improve speech understanding abilities of older listeners in adverse listening conditions. Thus, the proposed research is relevant to NIH's mission to develop fundamental knowledge that will reduce the burdens of human disability.
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