Voice Onset Time before and after STN-surgery
in patients with Parkinson’s disease
Joel Åkesson, Jonas Lindh, Emilia Carlsson, Lena Hartelius
Division of Speech and Language Pathology, Institute of Neuroscience and Physiology, University of Gothenburg, Sweden
Background
Purpose
Nearly 90% of individuals with Parkinson's disease (PD) develop
dysarthria during the course of their illness. The hypokinetic
dysarthria characteristic of PD has audible symptoms such as soft
breathy monotonous voice, imprecise consonant articulation and
variable speech rate.
Surgical treatments, including deep brain stimulation (DBS), most
commonly performed in the subthalamic nucleus (STN) are
becoming more frequent, and although its effect on gross motor
function is impressive, its effect on speech can be non-existent or
even detrimental.
In documenting dysarthria and hence evaluating treatment effects,
acoustic analysis is a precise, reliable instrumental method that
permits quantification of subtle signs of speech deviation. Acoustic
analysis has been described as a potential biomarker of early
disease progression.
The purpose of the present study was to measure Voice Onset
Time (VOT) in syllable repetition task performed before and
after STN surgery in 14 individuals with Parkinson’s disease.
Fig. 1 VOT measurement from the initial burst of the plosive /p/ to the onset of the
vocal fold vibration of the following vowel.
Results
A statistically significant increase in VOT mean was found for
/p/ and /k/ post surgery as well as a statistically significant
increase in the standard deviation of VOT in both AMR and
SMR syllable repetitions. Men had significantly longer mean
VOTs compared to women. In addition, there was a statistically
significant increase in percentage unmeasurable VOTs post
surgery in both AMR and SMR syllable repetitions.
Table 1. Significant differences (p-values) pre- compared to post surgery, n=14.
pa
0.0007***
0.0045**
VOT mean
VOT standard
deviation
Percentage
0.0006***
unmeasurable VOTs
ta
0.1686
<0.0001***
ka
0.0365*
0.0272*
0.0061**
0.0402*
Method
Participants
All patients subjected to bilateral STN-surgery at Sahlgrenska
University Hospital between 1999 and 2009 with consistent and
high-quality recordings including syllable repetition were selected
for analysis. The recorded group included 7 men and 7 women,
mean age was 68 years and ranged between 52 and 75 years.
Speech sample
Participants were digitally recorded performing a syllable repetition
task including both alternating motion rates (AMR, i.e. papapapa,
tatatata and kakakaka) and sequential motion rates (SMR, i.e.
patakapataka) before and at different set times after surgery (most
frequenty 6 and 12 months +- 1 month. One participant was
recorded 36 months after surgery.)
Statistical analysis
Multiple regression analysis was used to determine differences
between pre- and post data, as well as differences between the
three consonants and possible gender effects.
Acoustic analysis
VOT is an acoustic parameter which reflects timing control
between phonatory and articulatory aspects of speech production.
It is defined as the time between the initial burst of the release of a
plosive [p, t, k] and the first noticeable and regularly occurring
period relating to the vocal fold onset of vibration of the following
vowel [a] (see Figure). VOT was measures using the software
Praat (Boersma & Weenink, 2012).
For additional information, please contact:
Name: Lena Hartelius, professor
E-mail: [email protected]
Website: www.sahlgrenska.gu.se/logopedi
Conclusions
Although the investigated group with Parkinson’s
disease was small, there was a clear indication that
articulatory precision, as measured by VOT, was
significantly negatively affected as an effect of STN
surgery. VOT tended to increase after surgery,
being more variable and articulatory precision
decreased. This can be interpreted as slower
articulatory movements performed with less
precision and more variability which may result in
a VOT being a less reliable cue for listeners.