Temporal envelope expansion of speech in noise for normal-hearing and hearing-impaired listeners: effects on identification performance and response times.

The effects of expanding the temporal envelope of speech sounds on speech identification in noise were investigated in normal-hearing and hearing-impaired listeners. Expansion was performed by applying a power-law transformation to the low-frequency temporal modulations (<500 Hz) of vowel-consonant-vowel logatomes presented against a background noise. Stimuli were spectrally degraded, allowing a direct examination of the perceptual effects induced by the modification of the temporal envelope alone on speech reception. This study extended a previous study conducted by Lorenzi et al. [1999. Hear. Res. 136, 131--138] by measuring the effects of envelope expansion on both identification performance and response times in normal-hearing and hearing-impaired listeners. Overall, the results show that temporal expansion yields only small improvements in identification scores (approximately 5%) in normal-hearing listeners. No effect of expansion on identification scores was observed in hearing-impaired listeners. On the other hand, the results show that expansion led to a significant decrease in response times in both normal-hearing and hearing-impaired listeners. The average benefit from expansion was about 65 ms in both groups. These results suggest that expanding the temporal envelope of speech sounds presented in noise may improve 'ease of listening' in both normal-hearing and hearing-impaired listeners.