1 research outputs found
The form and auditory control of downward trends in intonation
Of all the areas of intonational research, study of the tendency of the
frequency of vocal fold vibration to decline during the course of an utterance
- F0 declination - is likely initially to be the most fruitful in determining the
interaction between perceptual and productive processes. A general
introduction to the phenomenon is augmented by analysis of different
methods of determining declination lines; theoretical treatments are then
introduced. One particular local factor contributing to the downward trend,
downstep, is discussed, and its pivotal role in the intonational phonology
developed by Janet Pierrehumbert critically examined. In the light of the
theoretical discussion, two competing hypotheses are presented as to the
mediation of the declination effect, which is the effect that of two accented
syllables in an utterance, the second has to have a lower peak F0 value than
the first for them to be judged to have equal prominence. The Global
Declination Hypothesis attributes this to the use by speakers and hearers of
one or two abstract reference lines declining through the course of a tone-unit.
The Local Declination Hypothesis attributes it to the disposition of F0
excursions surrounding the two accents as well as to the respective peak
values.
The Global Declination Hypothesis is tested by presenting listeners with
pairs of dual-peak accented utterances with the two peaks identical in F0,
without any physically present local declination, and asking them to rate the
prominence of the second peak of each such utterance. No significant
differences are found in the prominence ratings, so the Local Declination
Hypothesis appears to be favoured. That hypothesis is itself tested through
the development of a model of individual accent prominence, which
incorporates terms for surrounding unaccented context. This is then used
as the basis of a model of the perceptual constraints on the production of
intonation in the scaling of target peaks. The model predicts that local slope
between accents and slope of the context after the target accent, as well as
other local variables, jointly determine the F0 value of a peak with a
particular targetted prominence relationship with its predecessor. If the
interaccentual stretch is declining, the declination effect is predicted to
occur, ceteris paribus. The model is found to be initially acceptable. In
addition, a global interpretation of downstep is made within the model.
The mechanisms the model is suggested to represent are auditory feedback
control loops of a variety of possible degrees of complexity. An experiment
is devised to test for the basic existence of a feedback loop which is used to
prevent local slope exceeding an arbitrary threshold value. Auditory
feedback In subjects was disrupted by headphone-administration of low-pass
filtered masking noise during their utterance of a sustained vowel, and a
short and a long dual peak-accented sentence. The disruption was sufficient
to alter the apparent mechanism controlling the production of the sustained
vowel, but the Lombard effect, whereby subjects automatically raise the level
of their voice in ambient noise, was found to be a vitiating factor.
General conclusions are drawn on the nature of the declination phenomenon
In intonation, and proposals made for future research