ASA 127th Meeting M.I.T. 1994 June 6-10

5aPP11. Spectral enhancement using a two-filter model of impaired frequency selectivity.

Michael A. Stone

Brian C. J. Moore

Dept. of Exptl. Psychol., Univ. of Cambridge, Downing St., Cambridge CB2 3EB, UK

Neural tuning curves can be described as comprising two shapes: a narrow ``tip'' filter with high sensitivity, and a wider ``tail'' filter with lower sensitivity. When cochlear function is impaired, the sensitivity of the tip filter decreases. The tail filter characteristics are difficult to measure in normal-hearing subjects using psychophysical techniques such as the notched-noise method. However, with mild to severe cochlear hearing loss, the tail filter has a greater influence on the results, and becomes easier to measure. Auditory filter shapes were estimated using the notched-noise method over a wide range of center frequencies for subjects with differing degrees of hearing loss. These data were used to construct a model that predicts typical filter shapes as a function of frequency and hearing loss. The model is being used to improve the accuracy of a spectral contrast enhancement method intended to compensate for the effects of reduced frequency selectivity. The method is similar to one also being developed in this laboratory [T. Baer and B. C. J. Moore, this meeting], but uses a filter bank rather than overlap-add FFTs. Results of intelligibility tests using speech in speech-shaped noise, enhanced by this method and tested on hearing-impaired subjects, will be described. [Work supported by the MRC.]