MULTIMICROPHONE MONAURAL AIDS FOR THE HEARING IMPAIRED

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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 hearing-impaired subjects function more effectively in complex environments containing interference and reverberation. The more immediate goal is the creation of multimicrophone systems that enhance monaural speech reception in such environments. This research, combined with research on binaural interaction in impaired listeners, will provide solid background for the development of multimicrophone aids to assist impaired listeners who have significant hearing in either one or two ears. To enhance monaural speech reception, we envision a microphone array that resolves the incoming signals into simultaneous directional channels, followed by a directional coding operation that transforms these signals in such a way that resolution is preserved at the perceptual level after the signals are summed for presentation to a single ear. Proposed work on the microphone array focuses on the creation of a single directional channel and reduction of interference from sources directionally distinct from the target source. The interference reduction schemes to be studied draw heavily from previous work on antenna theory and binaural hearing and include both fixed and adaptive, and linear and nonlinear, signal- processing algorithms. Based on positive results already obtained in this program, a subset of these schemes will be implemented in wearable devices for field testing. Proposed work on directional coding includes study of the coding effectiveness of differential filtering, variations in voice quality, and extrapolations of these variations by signal processing. Also, for use as a comparative reference, the coding effectiveness of variations in binaural lateralization (the natural coding method) will be examined. Many of our results on the reduction of interference will be applicable to cochlear-implant aids and sensory-substitution aids as well as conventional acoustic aids.