The project proposes a program of studies in speech perception and auditory psychophysics to examine the hypothesis that many of the difficulties in speech understanding among elderly listeners can be attributed to underlying problems in auditory temporal processing. Research indicates that elderly listeners have particular difficulty understanding speech that is degraded by the presence of background noise, or by various forms of temporal waveform distortion (e.g., time compression, interruption, reverberation). The listeners' problems may be related to the effects of presbycusic hearing loss, as well as diminished processing capacity within central stages of the auditory system. The project investigates the problem with experiments that examine the relative contributions of age- related changes in peripheral hearing sensitivity, central auditory function, and selected cognitive abilities using speech and non-speech stimuli. The project comprises four stages of investigation, each consisting of a series of speech recognition experiments and psychoacoustic discrimination tasks. Stage 1. (mos. 1-16) examines relations between speech recognition with four types of temporally-altered speech and several psychoacoustic measures of temporal sensitivity derived with simple tonal stimuli; Stage 2. (mos 13-36) examines the influence of auditory central processing factors by varying the complexity of stimuli used in both the speech and psychoacoustic tasks; Stage 3. (mos. 32-48) evaluates the effects of task demands and selected cognitive factors on listeners' serial recall of speech sentences and non-speech sequential patterns; Stage 4. (mos. 49-60) applies discriminant analysis statistical techniques to formulate profiles of temporal processing abilities of young and elderly listeners. For each stage of the investigation, the independent effects of age and hearing loss on listener performance are evaluated by testing young and elderly subjects with normal hearing and matched degrees of sensorineural hearing loss. Subjects participating in the project will also be examined on educational and language background, physical and mental health, and otologic history.
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