UBC Theses and Dissertations
The effect of acoustic cue redundancy on the perception of stop consonants by older and younger adults Carter, Nathaniel Ryan
Speech recognition is known to become more difficult as aging progresses. Though age-related hearing loss accounts for a significant portion of this difficulty, changes in cognitive processing and in the central auditory nervous system are also thought to contribute. Age-related speech recognition declines become most apparent for complex speech signals in which acoustic cues may be degraded, missing, or misaligned temporally. Each phoneme normally contains multiple, redundant acoustic cues signaling its presence and identity. The redundancy hypothesis suggests that older listeners require this natural redundancy of acoustic cues to a greater extent than do younger listeners, and it is the paucity of redundant cues within complex signals that makes them especially difficult for older listeners. The main purpose of the present study was to determine whether age-related redundancy effects existed when only single or dual acoustic cues signaled the presence of a stop consonant. Closure gap and release burst amplitude were varied for two phoneme contrast pairs (/p/ in speed/seed and /t/ in steam/seam) constructed from natural recordings. Six older and 6 younger participants with normal hearing (better than 25 dB HL from 250-4000 Hz) were tested. Using a 2-alternative forced choice (AFC) paradigm, participants indicated whether they heard the word as containing the stop consonant or not. ANOVA of the results revealed a main effect of burst amplitude and inconsistent effects of age but no interaction between burst amplitude and age, p = .803 for /p/ and .232 for /t/. For those steam/seam contrast stimuli in which closure gap was the only cue to stop presence, older listeners reached threshold perception of /t/ as gap duration increased but younger listeners did not. Because they do not show an interaction between age and the presence of redundant acoustic cues, these combined patterns of results do not support the redundancy hypothesis. They suggest rather that older and younger listeners with comparable hearing make similar use of the redundant presence of stop closure gap and consonant release bursts.
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