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Title: Factors affecting the perception of noise-vocoded speech : stimulus properties and listener variability
Author: McGettigan, Carolyn
ISNI:       0000 0004 2673 423X
Awarding Body: University of London
Current Institution: University College London (University of London)
Date of Award: 2008
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This thesis presents an investigation of two general factors affecting speech perception in normal-hearing adults. Two sets of experiments are described, in which speakers of English are presented with degraded (noise-vocoded) speech. The first set of studies investigates the importance of linguistic rhythm as a cue for perceptual adaptation to noise-vocoded sentences. Results indicate that the presence of native English rhythmic patterns benefits speech recognition and adaptation, but not when higher-level linguistic information is absent (i.e. when the sentences are in a foreign language). It is proposed that rhythm may help in the perceptual encoding of degraded speech in phonological working memory. Experiments in this strand also present evidence against a critical role for indexical characteristics of the speaker in the adaptation process. The second set of studies concerns the issue of individual differences in speech perception. A psychometric curve-fitting approach is selected as the preferred method of quantifying variability in noise-vocoded sentence recognition. Measures of working memory and verbal IQ are identified as candidate correlates of performance with noise-vocoded sentences. When the listener is exposed to noise-vocoded stimuli from different linguistic categories (consonants and vowels, isolated words, sentences), there is evidence for the interplay of two initial listening 'modes' in response to the degraded speech signal, representing 'top-down' cognitive-linguistic processing and 'bottom-up' acoustic-phonetic analysis. Detailed analysis of segment recognition presents a perceptual role for temporal information across all the linguistic categories, and suggests that performance could be improved through training regimes that direct attention to the most informative acoustic properties of the stimulus. Across several experiments, the results also demonstrate long-term aspects of perceptual learning. In sum, this thesis demonstrates that consideration of both stimulus-based and listener-based factors forms a promising approach to the characterization of speech perception processes in the healthy adult listener.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available