Page 260 - DENG504_LINGUISTICS

Linguistics

Notes here suggests that some element of rhythm production is based in the right hemisphere, although
further studies, including those considering LHD patients are necessary to further strengthen this
conclusion.

Relationship of RHD speaker's rhythm to that found in other neurological conditions
It is interesting to note that the speech of individuals with Foreign Accent Syndrome (FAS) and
ataxic dysarthria have both been described as more syllable-timed than that of normal controls.
Speakers with Foreign Accent Syndrome appear to speak with a foreign accent after a stroke. In
the majority of cases damage is to the left hemisphere, and in these cases, prosody is the feature
of speech most usually described as contributing towards the perceived foreign accent. In particular,
rhythm is often described as being more syllable-timed when English speakers develop FAS.
Dankovi?ová et al. summarise a number of features which may lead to the impression of syllable
timing. These features include: more equal syllable durations, non reduction of unstressed vowels,
insertion of vowels, misplacement of lexical stress and reduced intensity of stressed syllables.
Interestingly, however, when Dankovi?ová et al. investigated the speech of a patient with FAS
arising from RHD they found little prosodic disturbance, a point that will be returned to shortly.
Speakers with ataxic dysarthria have also been described as having a more syllable-timed rhythm on
the basis of impressionistic analyses. Using an early forerunner of the PVI, Ackerman and Hertrich
and Kent, found little evidence of syllable timing for this population. However, the metric used
appears to be overly sensitive to the durations of individual syllables. By contrast Stuntebeck used
the PVI and found lower values for a group of speakers with ataxic dysarthria than for a similar
group of healthy control participants, thus supporting the perceptual impressions of syllable timing.
It is somewhat of a puzzle why three different neurological conditions should all lead to impairment
in rhythm. Whilst the focus in this study is on RHD, the cases of FAS have usually involved LHD,
and ataxic dysarthria is usually attributed to damage of the cerebellum. Furthermore the case of
FAS in a person with RHD reported by Dankovi?ová et al. showed little prosodic disturbance of
any kind. It is possible that these different findings demonstrate that rhythm cannot be strictly
lateralised to one hemisphere, or, as many different factors may lead to syllable timing, that these
different factors are differently lateralised. It is also interesting that the same type of disturbance,
that is more syllable-timed rhythm, is found in each case. This may simply be because English is
so strongly stress-timed that any disruption tends in the opposite direction. It would, therefore,
be interesting to examine these neurological conditions in speakers of strongly syllable-timed
languages to see if their rhythm becomes more stress-timed. The answers to these questions are
beyond the scope of this paper and await further work to apply the PVI to different populations,
and to clients with different native languages.
It is possible that speakers with ataxic dysarthria and FAS also have a 'less stress-timed' rather
than a syllable timed rhythm per se, although further evidence is needed in the form of PVI
measures compared to those of normal participants in several languages.

Issues in analysis
These results are interesting and suggest a number of conclusions about prosody production in
speakers with RHD. However, they must be treated with sufficient caution for a number of
reasons. Firstly, only one speaker and one control participant were analysed, and there is always
the possibility that these speakers are not representative of their respective populations. However,
the control participant's results fit well with those found for British English, and the speech of the
speaker with RHD presents similarly to other brain damaged populations that have been associated
with syllable-timing. Secondly, the nature of the speech task is somewhat uncontrolled which is
rather different to previous applications of the PVI which have been conducted on carefully
controlled speech. Although the speakers in the present study are asked the same questions they
necessarily give different answers, meaning that the data analysed is not lexically identical.

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