This dissertation looks at motor control in speech production. Two specific questions
emerging from the speech motor control literature are studied: the question
of articulatory versus acoustic motor control targets, and the question of whether
prosodic linguistic variables are controlled in the same way as segmental linguistic
variables.
In the first study, I test the utility of whispered speech as a tool for addressing
the question of articulatory or acoustic motor control targets. Research has been
done probing both sides of this question. The case for articulatory specifications
is developed in depth in the Articulatory Phonology framework of Haskins researchers
(eg. Browman & Goldstein 2000), based on the task-dynamic model
of control presented by Saltzman & Kelso (1987). The case for acoustic specifications
is developed in the work of Perkell and others (eg Perkell, Matthies,
Svirsky & Jordan 1993, Guenther, Espy-Wilson, Boyce, Matthies, Zandipour &
Perkell 1999, Perkell, Guenther, Lane, Matthies, Perrier, Vick,Wilhelms-Tricarico
& Zandipour 2000). It has also been suggested that some productions are governed
by articulatory targets while others are governed by acoustic targets (Ladefoged
2005).
This study involves two experiments. In the first, I make endoscopic video
recordings of the larynx during the production of phonological voicing contrasts
in normal and whispered speech. I discovered that the glottal aperture differences
between voiced obstruents (ie, /d) and voiceless obstruents (ie, /t) in
normal speech was preserved in whispered speech. Of particular interest was the
observation that phonologically voiced obstruents tended to exhibit a narrower
glottal aperture in whisper than vowels, which are also phonologically voiced.
This suggests that the motor control targets of voicing is different for vowels than
for voiced obstruents. A perceptual experiment on the speech material elicited in the endoscopic recordings elicited judgements to see whether listeners could
discriminate phonological voicing in whisper, in the absence of non-laryngeal
cues such as duration. I found that perceptual discrimination in whisper, while
lower than that for normal speech, was significantly above chance. Together, the
perceptual and the production data suggest that whispered speech removes neither
the acoustic nor the articulatory distinction between phonologically voiced
and voiceless segments. Whisper is therefore not a useful tool for probing the
question of articulatory versus acoustic motor control targets.
In the second study, I look at the multiple parameters contributing to relative
prominence, to see whether they are controlled in a qualitatively similar way to
the parameters observed in bite block studies to contribute to labial closure or
vowel height. I vary prominence by eliciting nuclear accents with a contrastive
and a non-contrastive reading. Prominence in this manipulation is found to be
signalled by f0 peak, accented syllable duration, and peak amplitude, but not
by vowel de-centralization or spectral tilt. I manipulate the contribution of f0 in
two ways. The first is by eliciting the contrastive and non-contrastive readings in
questions rather than statements. This reduces the f0 difference between the two
readings. The second is by eliciting the contrastive and non-contrastive readings
in whispered speech, thus removing the acoustic f0 information entirely. In the
first manipulation, I find that the contributions of both duration and amplitude
to signalling contrast are reduced in parallel with the f0 contribution. This is a
qualitatively different behaviour from all other motor control studies; generally,
when one variable is manipulated, others either act to compensate or do not react
at all. It would seem, then, that this prosodic variable is controlled in a different
manner from other speech motor targets that have been examined. In the
whisper manipulation, I find no response in duration or amplitude to the manipulation
of f0. This result suggests that, like in the endoscopy study, perhaps
whisper is not an effective means of perturbing laryngeal articulations
