JCPSLP vol 14 no 3 2012

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Technology
JCPSLP Volume 14, Number 3 2012 129
Christine Taylor
(top), Vanessa
Aird (centre) and
Emma Power
This article
has been
peer-
reviewed
Keywords
ACOUSTIC
ANALYSIS
ASSESSMENT
DYSARTHRIA
TECHNOLOGY
TRAUMATIC
BRAIN INJURY
Weisiger, 1987). Kent (1996) provided a comprehensive
review of factors that undermine reliability of perceptual
judgements within and across clinicians. For example, our
accuracy of judgements is vulnerable to effects of drift over
time, as one becomes more familiar with a client’s speech,
as well as our level of expertise and familiarity with the
possible range of severity.
Several researchers have developed objective measure­
ment protocols to address problems with perceptual
judgements but, generally, these have not made their way
into routine clinical practice (Kent & Kim, 2003; Ludlow &
Bassich, 1984; Murdoch, 2011). Barriers may include
perceived or real difficulties with access to technical
equipment, reduced expertise, entrenched clinical practices,
and lack of time to collect and analyse objective measures.
Also, it has been argued that some objective measures
(e.g., vocal jitter or shimmer) may not correlate well with
perceptual features (e.g., vocal roughness or harshness)
(Bhuta, Patrick, & Garnett, 2004). One possible reason for a
low relationship for some measures may be the use of
nonspeech or quasi-speech tasks or simple word-level tasks
to avoid the highly varied nature of connected speech.
In the contemporary delivery of health care, where
accountability is paramount, the use of objective
measurements can strengthen our assessment methods
and tracking of improvement. Understanding which
measures have a strong relationship to perceptual
features at all levels of speech production is critical to this
endeavour. A comprehensive review of such measures
is beyond the scope of this paper and several excellent
overviews are already available (e.g., Kent, Weismer, Kent,
Vorperian, & Duffy, 1999; Thompson-Ward & Theodoros,
1998). Instead, we will provide a brief overview of some
acoustic measures developed for measuring vocal quality
and prosody, features commonly affected in dysarthria.
When evaluating vocal quality, one usually measures
fundamental frequency (f0) and intensity, and signal to
noise ratios in a stable production task (e.g., sustained ah )
to capture features such as habitual pitch, hoarseness,
and breathiness. Frequency measures quantify the rate,
range, and variability of vocal fold vibration. Jitter and
shimmer measure cycle-to-cycle change in frequency and
amplitude, respectively, with elevated values thought to
indicate pathology (Kent et al., 1999). High jitter values
may correlate with perceived roughness (Colton, Casper, &
Leonard, 2006; but see Bhuta et al., 2004). Harmonics-to-
noise ratio (HNR) reflects abnormal vibratory characteristics
of the folds and correlates with perceived hoarseness (e.g.,
Speech pathologists typically use perceptual
features and clusters of features to diagnose
dysarthria type. Although ecologically valid,
perceptual assessment remains largely
subjective. This paper describes a sample of
readily available acoustic measures and their
perceptual correlates that can be applied in
the clinical setting in order to objectively
evaluate the degree of impairment and
outcomes of intervention. The speech of
three individuals with acquired dysarthria
secondary to traumatic brain injury was
perceptually rated for diagnosis. The samples
were then analysed acoustically using
measures that potentially quantify these
perceptual features. Results indicated that
most features were well quantified by an
acoustic measure(s), while others were less
clear. Some acoustic measures may be less
sensitive to mild impairments while more
extensive normative data are required for
other measures. However, the acoustic
measures used here provide a starting point
to objectively describe dysarthric features,
document treatment outcomes, and support
accountability in service provision.
Dysarthria is a disorder of speech motor control that
affects one-third of individuals with traumatic brain
injury (TBI) (Duffy, 2005). Dysarthria has a significant
and sustained effect on quality of life. People with dysarthria
have a reduced ability to communicate effectively in
everyday activities, which can lead to social, vocational and
life participation restrictions (WHO, 2001). The current gold
standard for clinical diagnosis of dysarthria is subjective
perceptual judgement of speech behaviours across a range
of tasks. Perceptual measures are considered of highest
value in terms of ecological validity (Duffy 2005). However,
characterising dysarthria types can present challenges
due to the inherent variability seen both within and across
speakers. In addition, inter-rater agreement among non-
expert clinicians on presence and severity of perceptual
speech dimensions can be as low as 50–60% (Zyski &
Objective measurement of
dysarthric speech following
traumatic brain injury
Clinical application of acoustic analysis
Christine Taylor, Vanessa Aird, Emma Power, Emma Davies, Claire Madelaine, Audrey McCarry, and Kirrie
J. Ballard