Why does Speech Understanding in Noise Decline with Age? The Contribuition of Age-related Differences in Auditory Priming, Stream Segregation, and Listening in Fluctuating Maskers

Competing speech seems to pose a greater challenge to spoken language comprehension than does competing noise, especially for older adults. The difficulties of older adults may be due to declines in auditory and cognitive processing. However, evidence suggests that the use of top-down information processing to overcome this interference may be preserved in aging. This research investigated the effect of speech- and noise masking on language comprehension, as well as age-related differences in the use of top-down processing to overcome masking. Topic I examined whether younger and older adults gain the same release from masking given a partial preview of a target sentence in quiet (auditory prime) prior to hearing the full sentence in noise, and investigated the auditory factors contributing to the advantage provided by the primes. Results showed that despite age-related declines in overall performance, younger and older listeners benefited similarly from priming. This benefit was not attributable to cues about the target talker’s voice or fluctuations in the amplitude envelope of the target sentences. Topics II and III examined the effect of speech- and noise masking on the time-course of stream segregation. The analyses revealed that stream segregation takes time to build up when a speech target is masked by other speech, but not when it is masked by noise. Subsequent analyses showed that in younger adults, the delay in segregation under speech masking was primarily due to the vocal similarities between the talkers, with interference from the semantic content of the masker playing a secondary role in impeding performance. The results also showed that older listeners were less efficient than younger listeners in segregating speech from speech-like maskers. Furthermore, older listeners benefited less than younger listeners when the amplitude envelope modulations of maskers were limited. Overall, the findings indicate that some of the language comprehension difficulties experienced by older listeners in noisy environments may be due to age-related declines in stream segregation and a decreased ability to benefit from fluctuations in the amplitude envelopes of maskers. However, benefit from priming may help offset some of these age-related declines in auditory scene analysis.Ph