Enhanced speech perception at low signal-to-noise ratios with multichannel compression hearing aids

The effect of the signal-to-noise ratio (S/N) on speech discrimination was measured for two types of hearing-aid amplification, (1) full-range multichannel compression with eight independent frequency bands and (2) frequency-equalized linear amplification. Signal-to-noise ratios from -5 to 15 dB with speech-spectrum noise (at 70 dB SPL) and two voices (male and female) were used. The effect of S/N differed for the two aid types: As the S/N decreased, speech discrimination became relatively better with the multichannel compression hearing aid (MCCHA) in comparison to the linear amplification hearing aid (LAHA). Furthermore, this shift in MCCHA-LAHA performance occurred for every subject, independent of which aid produced better overall performance. Of 16 hearing-impaired subjects, 7 showed significantly better overall speech discrimination with the MCCHA than with the LAHA, 5 showed no difference, and 4 showed significantly better discrimination with the LAHA. Hearing-loss severity and MCCHA performance also were related: Subjects with less severe impairments showed greater improvement with the MCCHA. In a normal-hearing listener, the speech discrimination deficit produced by these MCCHAs was small and not statistically significant in most cases. Taken together, these results indicate that a full-range eight-channel MCCHA, for a mild to moderately severe hearing loss, causes little information degradation and can be of great benefit for speech discrimination in noise, particularly at low S/N.