Abstract: What do speakers do when they start to talk? This thesis concentrates
on the articulatory aspects of this problem, and offers methodological and experimental
results on tongue movement, captured using Ultrasound Tongue
Imaging (UTI).
Speech initiation occurs at the start of every utterance. An understanding
of the timing relationship between articulatory initiation (which occurs first)
and acoustic initiation (that is, the start of audible speech) has implications for
speech production theories, the methodological design and interpretation of
speech production experiments, and clinical studies of speech production.
Two novel automated techniques for detecting articulatory onsets in UTI
data were developed based on Euclidean distance. The methods are verified
against manually annotated data. The latter technique is based on a novel way
of identifying the region of the tongue that is first to initiate movement.
Data from three speech production experiments are analysed in this thesis.
The first experiment is picture naming recorded with UTI and is used to explore
behavioural variation at the beginning of an utterance, and to test and develop
analysis tools for articulatory data.
The second experiment also uses UTI recordings, but it is specifically designed
to exclude any pre-speech movements of the articulators which are not
directly related to the linguistic content of the utterance itself (that is, which
are not expected to be present in every full repetition of the utterance), in order
to study undisturbed speech initiation. The materials systematically varied the
phonetic onsets of the monosyllabic target words, and the vowel nucleus. They
also provided an acoustic measure of the duration of the syllable rhyme. Statistical
models analysed the timing relationships of articulatory onset, and acoustic
durations of the sound segments, and the acoustic duration of the rhyme.
Finally, to test a discrepancy between the results of the second UTI experiment
and findings in the literature, based on data recorded with Electromagnetic
Articulography (EMA), a third experiment measured a single speaker
using both methods and matched materials.
Using the global Pixel Difference and Scanline-based Pixel Difference analysis
methods developed and verified in the first half of the thesis, the main
experimental findings were as follows. First, pre-utterance silent articulation is
timed in inverse correlation with the acoustic duration of the onset consonant
and in positive correlation with the acoustic rhyme of the first word. Because
of the latter correlation, it should be considered part of the first word. Second,
comparison of UTI and EMA failed to replicate the discrepancy. Instead, EMA
was found to produce longer reaction times independent of utterance type.Keywords: Speech initiation, pre-speech articulation, delayed naming, ultrasound tongue imaging, electromagnetic articulography, automated methods
