Cheng, C.; (2012) Mechanism of extreme phonetic reduction: evidence from Taiwan Mandarin. Doctoral thesis , UCL (University College London).

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Abstract

Extreme reduction refers to the phenomenon where intervocalic consonants are so severely reduced that two or more adjacent syllables appear to be merged into one. Such severe reduction is often considered a characteristic of natural speech and to be closely related to factors including lexical frequency, information load, social context and speaking style. This thesis takes a novel approach to investigating this phenomenon by testing the time pressure account of phonetic reduction, according to which time pressure is the direct cause of extreme reduction. The investigation was done with data from Taiwan Mandarin, a language where extreme reduction (referred to as contraction) has been reported to frequently occur. Three studies were conducted to test the main hypothesis. In Study 1, native Taiwan Mandarin speakers produced sentences containing nonsense disyllabic words with varying phonetic structures at differing speech rates. Spectral analysis showed that extreme reduction occurred frequently in nonsense words produced under high time pressure. In Study 2a, further examination of formant peak velocity as a function of formant movement amplitude in experimental data suggested that articulatory effort was not decreased during reduction, but in fact likely to be increased. Study 2b examined high frequency words from three spontaneous speech corpora for reduction variations. Results demonstrate that patterns of reduction in high frequency words in spontaneous speech (Study 2b) were similar to those in nonsense words spoken under experimental conditions (Study 2a). Study 3 investigated tonal reduction with varying tonal contexts and found that tonal reduction can also be explained in terms of time pressure. Analysis of F0 trajectories demonstrates that speakers attempt to reach the original underlying tonal targets even in the case of extreme reduction and that there was no weakening of articulatory effort despite the severe reduction. To further test the main hypothesis, two computational modelling experiments were conducted. The first applied the quantitative Target Approximation model (qTA) for tone and intonation and the second applied the Functional Linear Model (FLM). Results showed that severely reduced F0 trajectories in tone dyads can be regenerated to a high accuracy by qTA using generalized canonical tonal targets with only the syllable duration modified. Additionally, it was shown that using FLM and adjusting duration alone can give a fairly good representation of contracted F0 trajectory shapes. In summary, results suggest that target undershoot under time pressure is likely to be the direct mechanism of extreme reduction, and factors that have been commonly associated with reduction in previous research very likely have an impact on duration, which in turn determines the degree of target attainment through the time pressure mechanism.

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