Page 258 - DENG504_LINGUISTICS

Linguistics

Notes section consists of the single segment /ð/. The first vocalic element, however, consists of the
vowel at the end of 'the' and the vowel at the start of 'elephant'. The pattern then alternates with
one vowel and one consonant in each successive interval until the sequence of three consonants
from the coda of 'elephant' and the onset of 'ran', which is treated as a single intervocalic interval.
In essence the raw intervocalic PVI (rInt) compares the duration of each intervocalic interval to the
duration of the next occurring intervocalic interval. The absolute difference, in milliseconds,
between the members of each pair is added, and the resulting figure is divided by the number of
pairs minus one. A normalised measure (nVoc) is used for vowels to take account of differences
in speech rate as described above. This normalised measure is essentially the same as the raw
calculation for intervocalic intervals except that the absolute difference between each pair is
expressed as a proportion of the mean duration of that pair. These proportions are added and
then the result is divided by the total number of pairs minus one. The resulting number is
fractional so is multiplied by 100 for easier comparison with the non-normalised figure for
intervocalic intervals. The equations for both the rInt PVI and nVoc PVI are given in the appendix.
For each participant 115 vocalic and 115 intervocalic intervals were measured (Grabe and Low
used between 118 and 205 intervals for each language studied. These measurements were taken
from around 90 seconds of speech in each case, which resulted in approximately fourteen hours of
acoustic analysis. The acoustic analysis was undertaken by the first author with reference to the
waveform and spectrogram using standard procedures for measuring duration (Fischer-Jørgensen
and Hutters, 1981; Peterson and Lehiste, 1960). The original PVI measure by Low et al. and Grabe
and Low was applied to read speech that had been recorded in a speech laboratory. Therefore,
because data for the current paper was conversation data recorded in non-laboratory situations, it
was necessary to make some decisions about how best to analyse the recorded material. Firstly,
because the recordings are of structured conversation, there are a number of pauses. These pauses
were not included in the analysis. When a speaker paused, the relevant segment's end point was
estimated as closely as possible. The duration of that consonant was then compared to the next
occurring intervocalic interval after the pause. Likewise, there is an occasional dysfluency. In
most instances it was possible to divide even these dysfluencies into sequences of vowels and
consonants whose durations are measured and treated in the same way as all the other durations.
Also, because the signal to noise ratio was lower than for laboratory speech, the visual displays
were sometimes difficult to interpret. In these cases more reliance was placed on listening in order
to mark the interval boundaries.
Results
The results of the analysis show that the control participant had higher overall PVI scores for both
vocalic and intervocalic measures than the speaker with RHD. The lower PVI values suggest
initially that the speaker with RHD spoke with more syllable-timed rhythm.
Discussion
This paper has compared the rhythm of a speaker with RHD to that of a neurologically normal
control using the pairwise variability index (PVI). The results show that the speaker with RHD
spoke with a more syllable-timed rhythm than the control, and that this result is significant for the
durations of intervocalic intervals.
18.6 Relationship of Control Participant's Results to Measures of
British English

The control participant had high PVI values for both nVoc and rInt, which suggests an extremely
stress-timed rhythm. Because this speaker is Australian, there is no other material available for
comparison (although the collection of this data is planned by the current authors). However, it
is enlightening to compare the results of the control participant to results available in the literature
for British English.

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