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Gap detection thresholds in old and young adults for speech and nonspeech stimuli differing in spectral properties Storzer, Edward


Older adults have more difficulty than younger adults understanding spoken language, especially in the presence of background noise and when the speech signal is degraded (e.g., CHABA, 1988). Such deficits exist even for older adults with audiometric hearing thresholds in the normal range (e.g., Pichora-Fuller, 1997). Temporal processing has been implicated as an important aspect of speech processing that is susceptible to age-related changes. Gap detection tasks measure one aspect of temporal processing by determining the smallest gap between two stimulus markers that can be detected by a listener. Characteristics of gap detection stimuli, including marker duration and spectral symmetry of markers, influence the degree to which a gap detection task approximates processing of phonetically important temporal speech cues. Manipulation of these features has been shown to affect listener performance (e.g., Phillips, Taylor, Hall, Carr, & Mosop, 1997). This thesis examines the influence of such stimulus characteristics on age-related effects in gap detection performance, and considers the implications of such interactions. Gap detection thresholds were measured for eight younger and eight older normal-hearing adult listeners. The stimuli were varied across three dimensions, which included (1) speech versus non-speech, (2) long duration markers versus short duration markers, and (3) symmetrical versus asymmetrical markers. Gap detection performance was measured for each participant in eight stimulus conditions, which included all possible combinations of the three varied stimulus characteristics. Results replicated past findings which indicate poorer gap detection performance in older adults compared to younger adults, independent of audiometric hearing loss (e.g., Schneider, Pichora-Fuller, Kowalchuk, & Lamb, 1994; Snell, 1997). This age difference was shown to be significantly greater when markers were asymmetrical, which is consistent with the view that older adults have particular difficulty in processing temporal cues which closely approximate those found in consonant-vowel combinations in real speech. In asymmetrical conditions, participants of all ages were shown to perform better in speech conditions, indicating the presence of processing cues intrinsic to real speech signals that are independent of the temporal and spectral characteristics matched between the speech and non-speech stimuli used in this study.

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