AUDITORY SUPPLEMENTS TO SPEECHREADING - COMBINING AMPLITUDE ENVELOPE CUES FROM DIFFERENT SPECTRAL REGIONS OF SPEECH

Many listeners with severe-to-profound hearing losses perceive only a narrow range of low-frequency sounds and must rely on speechreading to supplement the impoverished auditory signal in speech recognition. Pr evious research with normal-hearing subjects [Grant et al., J. Exp. Ps ychol. 43A, 621-645 (1991)] demonstrated that speechreading was signif icantly improved when supplemented by amplitude-envelope cues that wer e extracted from various spectral regions of speech and presented as a mplitude modulations of carriers with frequencies at or below the spee ch band from which the envelope was derived. This experiment assessed the benefit to speechreading provided by pairs of such envelope cues p resented simultaneously. In general, greater improvements in speechrea ding scores were observed for pairs than for single envelopes when the carrier signals were chosen appropriately. However, when pairs of env elope signals were transposed to low frequencies, the benefit to speec hreading was no better than-the most effective single-band envelope si gnal tested, or for a low-pass-filtered speech signal with the same ov erall bandwidth. Suggestions for improving the efficacy of frequency-l owered envelope cues for hearing-impaired listeners are discussed.