Use of temporal envelope cues in speech recognition by normal and hearing-impaired listeners

The temporal acuity of listeners with sensorineural hearing loss is currently a matter of some controversy. In this study, the ability of normal-hearing and hearing-impaired listeners to utilize temporal cues of speech was measured directly. In addition to natural (unprocessed) nonsense syllables, several processed-speech conditions were employed. Nonsense syllables were digitally processed to remove the original spectral information, resulting in a time-varying speech envelope amplitude modulating a noise carrier. The processed-speech conditions were the envelope of a broadband speech signal modulating a broadband noise, a low-pass speech signal modulating a low-pass noise, a high-pass speech signal modulating a high-pass noise, and a two-channel signal comprised of the low- and high-pass modulated signals combined. Recognition of the envelope stimuli in quiet and also in modulated and steady noise backgrounds was tested. Listeners were tested at presentation levels yielding their maximum performance on a syllable recognition task. The hearing-impaired listeners performed more poorly on a recognition task than the normal-hearing listeners for unprocessed speech signals. However, for listeners with hearing losses of either flat or sloping configuration, there was no significant deficit in their ability to use temporal cues in speech, even in frequency regions of hearing loss up to 70 dB HL. These results demonstrate that moderate to severe sensorineural hearing loss does not impair the temporal (nonspectral) acuity of listeners in terms of speech recognition, when audibility of the stimuli is compensated for.