Discrimination of Filtered-Clipped Speech by Sensorineural Hearing-Impaired Subjects

Abstract

A form of preprocessed speech known to be highly intelligible to normal listeners was heard by a group of subjects with sensorineural hearing losses. The preprocessing technique involves high-pass filtering (cutoff 1100 Hz, slope 12 dB/oct) and infinite amplitude clipping. Tests with normal listeners in this laboratory have shown that the resulting speech has an intelligibility of 97% under noise-free conditions and an intelligibility of 90% at a signal-to-noise level of 0 dB for PB words after training. Subjects with sensorineural hearing losses and average bilateral SRTs of 65 dB were tested using CID W-22 PB word lists. The subjects heard unmodified speech and then filtered-clipped speech, both at 15-dB sensation level. Discrimination scores for one group of subjects averaged 46% for unmodified and 61% for filtered-clipped speech. For the remaining subjects, presbycusis cases, scores were so variable as to defy analysis. Errors for unmodified speech were due mainly to misrecognition of stops, fricatives, and affiricates; errors for filtered-clipped speech were more frequently due to vowel substitutions and distortions. [Work supported by NIH and NASA.]