Vowel Acoustics in Individuals with Parkison's

Speech Science – Vowel Acoustics in People with Parkinson’s Parkinson’s disease is a neurodegenerative disease that contributes to the progressive decline of motor function because of loss of dopamine-creating brain cells. Given the progressive decline of motor function, this disease shows characteristics of hypokinetic dysarthria as well as major signs of rigidity, tremor, and bradykinesia. In light with these effects, vowel acoustics in people with Parkinson’s disease has attracted considerable attention in recent years. Actually, for many individuals with Parkinson’s disease, hypokinetic dysarthria is a common condition, which is an indicator of motor speech disorders. Numerous studies have been carried out to examine motor speech disorders in Parkinson’s disease, particularly in relation to hypokinetic dysarthria. This paper examines some studies that have been conducted to evaluate the issue of hypokinetic dysarthria in people with Parkinson’s disease with regards to vowel acoustics. The article provides a summary of the articles and critique of the methodological issues in the studies. Summary of Articles Skodda, Gronheit & Schlegel (2012) conducted a study in which they examined whether vowel articulation in people with Parkinson’s disease is an indicator of certain changes in the progression of the disease. The study was carried out on the premise that hypokinetic dysarthria in Parkinson’s disease is a multifaceted impairment that affects different aspects of an individual’s speech including articulation, respiration, prosody and phonation. These researchers utilized a quantitative research approach i.e. pre-test, post-test study through which research participants were divided into two groups i.e. experimental group and control group. Pre-test and post-test data was collected and analyzed from each of these two groups to help answer the research question. The researchers concluded that vowel articulation in patients suffering from Parkinson’s disease is an indicator of specific changes in the progression of the disease. Vowel articulation impairment was found to be independent from global motor function though linked to gait dysfunction, vowel articulation measurement may have a potential of acting as an indicator of progression of axial disease. Watson & Munson (2008) examine Parkinson’s disease and the impact of lexical components on vowel articulation. In this regard, lexical components are phonological neighborhood density and word frequency, which are considered significant in the perception and production of speech. The study employed a pre-test, post-test quantitative research methodology in which participants were grouped into two i.e. experimental groups and control groups. The experimental group comprised 10 men who are suffering from idiopathic Parkinson’s disease whereas the control group comprised 10 healthy individuals. Audio recording of individuals in the experimental group was carried out and data was measured using Mini-Mental-Scale-Examination. The study found that Parkinson’s disease significantly affects speech and generates a more complex interaction vowel production beyond what is established in existing literature. In concurrence with previous studies, individuals with Parkinson’s disease has vowel-space dispersion. While all participants in the experimental group suffered from hypokinetic dysarthria, speech impairment severity could not be established. Bang et al. (2013) conducted a research that examined acoustic attributes of vowel sounds in individuals suffering from Parkinson’s disease. The research was geared toward describing the acoustic speech and speech attributes of Parkinson’s disease patients. This research was conducted on the premise that hypokinetic dysarthria occurs in a significant portion of patients suffering from Parkinson’s disease. Similar to the other studies, Bang et al. (2013) employed a pre-test, post-test research methodology in which data was collected from the participants prior to and after being subjected to an experimental procedure. The experimental group included seven female Parkinson’s disease patients while the control group included seven normal healthy females. The experimental procedure involved requiring each participant in the two groups to vocalize extended /a/, /e/, /i/, and /u/ vowels three times for at least 5 seconds at a comfortable voice tones and loudness (Bang et al., 2013). Data collected from these participants was analyzed using statistical analysis and predictive analysis processes. The study found that Parkinson’s disease patients exhibit impairments in tongue movement and laryngeal function. Some of these laryngeal function variables include abnormal jitter, asymmetric centralization, and decreased vowel space area. Each of the three studies employed similar methodologies in exploring the issue of vowel acoustics in people with Parkinson’s disease. The use of a pre-test, post-test research design helped to effectively examining the vowel acoustics between people with Parkinson’s disease and healthy individuals. However, there were significant differences in the data analysis processes utilized by the authors and their data interpretation to arrive at the conclusions. For data collection, Skodda, Gronheit & Schlegel (2012) required each participant to perform a standardized reading task comprising four complex sentences. These participants were required to read the text twice in order to be familiar with it as the researchers digitally recorded the speech. On the contrary, Bang et al. (2013) required each participant to vocalize four extended vowels three times as they were recorded with a microphone and digital audio tape. Watson & Munson (2008) required study participants to read 32 CVC words with monophthongal vowels. Participants were given cards containing these words and required to read them aloud in a quasiransom order. Similar to the other studies, digital recording was used in this study as participants were required to read the cards three times, which contributed to 96 productions per study participant. Skodda, Gronheit & Schlegel (2012) analyzed data through the use of statistical analysis approaches just like the other researchers. However, these researchers employed ANOVA post-hoc t-test for independent and dependent samples and Pearson correlation for major correlations with p<0.01 as the adjusted level of significance. Watson & Munson (2008) used three-factor mixed-model ANOVA and carried out regression analyses of data obtained from the research participants. For Bang et al. (2013), data analysis involved the use of statistical analysis processes using SPSS Version 18.0 for Windows. Through this software, vowel sounds were compared using Mann-Whitney U-Test with statistically significant values of p<0.05. Critique of the Articles While each of these studies provide significant insights regarding the issue of vowel acoustics in people with Parkinson’s disease, there are some significant issues relating to interpretation of data and general conclusions. Skodda, Gronheit & Schlegel (2012) utilized a relatively large sample size that seemingly generated difficulties in data collection and interpretation. Even though the researchers also relied on some previous research findings, the inclusion of 67 patients in the study was relatively large and generated complexities in data collection and interpretation. Additionally, the recruitment of study participants for a long period of time i.e. from 2002 to 2011 could have impacted the findings with respect to the health of the participants. The prolonged period of time for recruitment had significant impacts on the findings through influencing how Parkinson’s disease affects the speech capabilities of the individual. The authors of this research do not provide a specific conclusion from the study, but simply discuss their research findings. It is relatively difficult for the reader to determine a specific, precise conclusion of the study in relation to the phenomenon under investigation. In their study, Watson & Munson (2008) did not review existing literature on the issue of Parkinson’s disease and the impact of lexical factors on vowel articulation. Even though pre-test, post-test research design was employed, the researchers did not provide a comparison of data collected before and after the experiment. This study would have benefited from a comparison of data from the experimental group prior to and after administering the experiment. This would have improved understanding of how Parkinson’s disease and lexical factors impart vowel articulation and other aspects of speech. A review of existing literature on the phenomenon under investigation would have provided a suitable foundation for examining the issue. In their study, Bang et al. (2013) used only four vowels as the premise for collecting data from the two groups of participants to help understand vowel acoustics in people with Parkinson’s disease. The four vowels used by these researchers were not complex enough to demonstrate the acoustic characteristics and speech difficulties experienced by patients suffering from this disease. This implies that the inclusion of more complex words, phrases or sentences could have an impact on the acoustic characteristics of vowel sounds by the participants. The potential impact would in turn generate different research findings as compared to those provided by these researchers in their study. In conclusion, the three studies provide significant insights on the issue of vowel acoustics in people suffering from Parkinson’s disease. These studies were carried out on the basis that hypokinetic dysarthria is a common condition among people with Parkinson’s disease. The researchers employed similar approaches i.e. pre-test, post-test research design in which study participants were grouped into two i.e. experimental group and control group. The study needs to collect more evidence on speech capabilities of patients with Parkinson’s disease and employ different research approaches. The use of different research approaches could help enhance understanding of the phenomenon under investigation through additional findings. References Bang, Y., Min K., Sohn, Y. H., Cho, S. (2013). Acoustic Characteristics of Vowel Sounds in Patients with Parkinson Disease. Journal NeuroRehabilitation, 32(3), 649-654. doi:10.3233/nre-130887 Skodda, S., Grönheit, W., & Schlegel, U. (2012). Impairment of Vowel Articulation as a Possible Marker of Disease Progression in Parkinsons Disease. PLoS ONE, 7(2). doi:10.1371/journal.pone.0032132 Watson, P. J., & Munson, B. (2008). Parkinson's disease and the effect of lexical factors on vowel articulation, Journal of the Acoustical Society of America, 124(5): EL291–EL295.doi:10.1121/1.2987464