Evidence for active control of tongue lateralisation in Australian English /l/ and its acoustic consequences

Abstract

This thesis provided new insights into lateral production by addressing the following questions: (1) what are the primary production goals of /l/; and (2) how do the articulatory goals of /l/ production relate to their acoustic properties? To investigate the production goals of /l/ and the articulatory-acoustic relation, a three-dimensional (3D) electromagnetic articulography (EMA) study was conducted with simultaneous acoustic recording. Six speakers were recorded. Sensors were located at key points on the midline and sides of the tongue to track lateralisation. The analyses made use of both mid-sagittal and para-sagittal articulographic measures. Target /l/s were elicited in two vowel contexts {/æ/ and /?/} and in two contrastive syllable positions: onset /l/s in CVC.l?C frames and coda /l/s in CVl.C?C frames. Context vowels /æ/ and /?/ were chosen because of the different constraints that they place on the shape of the tongue preceding /l/.The thesis consists of two experimental chapters. Chapter 3 reports how known variations in the timing of mid-sagittal gesture movements are related to para-sagittal dynamics in /l/ formation in Australian English. The articulatory analyses show that: (1) the temporal lag between tongue tip and tongue dorsum gestures identified in the mid-sagittal plane changes across different syllable positions and vowel contexts; (2) relative to the temporal lag between gestures in the mid-sagittal plane, the duration of para-sagittal lateralisation is stable across syllable positions and vowel contexts; and (3) the lateral channel is largely formed by tilting the tongue laterally as opposed to curving the tongue within the coronal plane. Chapter 4 investigated the acoustic properties associated with para-sagittal lateralisation in Australian English /l/. Degree of lateralisation was tracked over time, by comparing parasagittal tongue height to mid-sagittal height at the tongue blade. Analysis of the relationship between formant frequencies and degree of tongue lateralisation revealed a positive correlation between F3 values and tongue lateralisation on the dominant side. This finding indicates that acoustic characterization can be directly related to articulatory data. Tongue lateralisation is a strong predictor of F3 frequency.The results are interpreted as evidence that the formation of the lateral channel is under active control. The maximum of tongue lateralisation follows the target of tongue middle lowering/tongue dorsum retraction consistently across vowel and syllable contexts. Whereas every other measure was context dependent, the interval of lateralisation shows stability across contexts despite variation in other articulatory and acoustic phonetic measures.

Date of Award	2019
Original language	English