Speech recognition in amplitude-modulated noise of listeners with normal and listeners with impaired hearing

The effect of amplitude-modulated (AM) noise on speech recognition in listeners with normal and impaired hearing was investigated in two experiments. In the first experiment nonsense syllables were presented in high-pass steady-state or AM noise to determine whether the release from masking in AM noise relative to steady-state noise was significantly different between normal-hearing and hearing-impaired subjects when the two groups listened under equivalent masker conditions. The normal-hearing subjects were tested in the experimental noise under two conditions: (a) in a spectrally shaped broadband noise that produced pure tone thresholds equivalent to those of the hearing-impaired subjects, and (b) without the spectrally shaped broadband noise. The release from masking in AM noise was significantly greater for the normal-hearing group than for either the hearing-impaired or masked normal-hearing groups. In the second experiment, normal-hearing and hearing-impaired subjects identified nonsense syllables in isolation and target words in sentences in steady-state or AM noise adjusted to approximate the spectral shape and gain of a hearing aid prescription. The release from masking was significantly less for the subjects with impaired hearing. These data suggest that hearing-impaired listeners obtain less release from masking in AM noise than do normal-hearing listeners even when both the speech and noise are presented at levels that are above threshold over much of the speech frequency range.