Cross-Rate Variation in the Intelligibility of Dual-Rate Gated Speech in Older Listeners

Intelligibility of sentences gated with a single primary rate (0.5-8 Hz, 25-75% duty cycle) or gated with an additional concurrent rate of 24 Hz and a 50% duty cycle was examined in older normal-hearing and hearing-impaired listeners. With a stronger effect of age than hearing loss, intelligibility tended to increase with primary rate and duty cycle, but varied for dual-rate gating. Reduction in the total amount of speech due to concurrent 24 Hz gating had little effect on the intelligibility for the lowest and highest primary rates, but was detrimental for rates between 2 to 4 Hz, mimicking the pattern previously obtained from young normal-hearing listeners. The dual-rate intelligibility decrement with a 2 Hz primary rate significantly correlated with speech intelligibility in multi-talker babble, suggesting overlap of perceptual processes. Overall, findings reflect interaction of central and peripheral processing of speech occurring on different time scales.