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Speech perception by older listeners : contributions of auditory temporal processes Haubert, Natalie

Abstract

Auditory temporal processing is believed to be critical to speech perception; however, the exact nature of the contributing temporal processes and their psychophysical limits are as of yet undetermined. Furthermore, in light of the difficulties understanding spoken language that are common in older age, the resilience of these processes to normal aging warrants further investigation. Older adults, even with normal pure-tone hearing thresholds, often experience difficulty understanding spoken language when the message is presented in noise and/or when the rate of the message is increased. To further our understanding of these complaints, measures of temporal resolution and word identification were obtained from younger and older listeners. Eight younger and eight older normal-hearing listeners identified four word-pair continuums that varied from one word to another word as the duration of an inserted silent interval varied from short to long (i.e., 'cash' to 'catch'). These word-pairs were presented at both a slower and a faster speaking rate. The listeners identified these word-pair continuums, first, in a quiet listening condition; later they identified selected tokens from each continuum in three background noise conditions. These listeners also completed a gap detection task where five gap detection thresholds were obtained for a 2- kHz tone pip with gap-defining marker durations of 0.83, 5, 10, 80 and 400 ms. The present study replicates previous findings indicating that older adults are significantly poorer than younger adults at detecting gaps embedded in non-speech stimuli (2-kHz markers) when the surrounding material is short (Schneider & Hamstra, 1999; Schneider, Pichora-Fuller, Kowalchuk, & Lamb, 1994). Correspondingly, older adults were also shown to have greater difficulty identifying speech contrasts when a gap served to differentiate between two words, particularly for fast speech and in the context of background noise. Common to both these cases is the poorer performance evidenced by older listeners in the context of fast rates/ short duration stimuli. This pattern of findings is consistent with a hypothesis that proposes that recovery from neural adaptation occurs more slowly in the older compared to the younger auditory system (Schneider & Hamstra, 1999).

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