The ultimate goal of this research is the development of sensory aids that sample the acoustic environment at more than one point in space (multimicrophone aids) to help people with hearing impairments function more effectively in complex environments containing interference and reverberation. In particular, the proposed work is aimed at the development of multimicrophone systems that enhance the reception of a target speech source by reducing interference from sources directionally distinct from that of the target. The interference-reduction schemes to be studied are outgrowths of past work on both fixed directional, and adaptive noise-cancelling, microphone arrays. Much of the proposed work involves further algorithmic development of these interference-reduction systems, leading to robust, maximally-directive head-worn fixed arrays and to improved performance of adaptive arrays in reverberant and dynamically-changing environments. The multimicrophone systems under development are also being designed to allow user control of the 'look' direction, as well s to convey information about the background, i.e., the presence and location of non- target sources. Proposed methods for incorporating this background information include beam scanning and source selection. binaural, as well as monaural, output systems are under study for improved displays of target and background signals. Past evaluations of the physical performance of these systems, and prospects for further improvement, are promising. Little is known, however, about the use and benefit of directional and source-cancelling systems in everyday environments. Therefore, the proposed work is aimed at adapting algorithms for implementation in flexible real-time processors operating in conjunction with microphone arrays. These prototype hearing aids will be worn and evaluated in realistic acoustic conditions that incorporate reverberation and multiple interference sources, with natural temporal variations. Both speech intelligibility and the ability to monitor the acoustic environment will be assessed. Progress in this work will be directly applicable to similar problems of interference reduction for cochlear implants, sensory-substitution aids, and speech-input devices for the handicapped.
