The Effect of the Positioning of an Individual on Perturbation Measures and Durations of Prolonged Vowels in Female Scottish Speakers
Killips, E. (2014) The Effect of the Positioning of an Individual on Perturbation Measures and Durations of Prolonged Vowels in Female Scottish Speakers, no. 54.
Aim: Maximum Phonation Time (MPT) and measures of perturbation are clinically important as they are used as part of voice assessment in order to diagnose and plan management for clients (Mathieson, 2001). This study aimed to investigate whether the positioning of an individual (standing or sitting) during a vowel prolongation assessment had an effect on an individual's MPT and the associated measurements of perturbation (jitter and shimmer). This is of particular clinical interest as many factors have been shown to affect perturbation measures and MPT, however there is very little discussion about the effect of positioning within the literature. The researcher hypothesised that MPT would be longer when standing as the participants' vital capacity would be greater (Mathieson, 2001), and that there would be changes to the perturbation measures as the participants' head positioning would not be consistent for each repetition. Method: Eighteen Scottish speaking female participants aged between 20 and 40 years of age took part in this study. The participants were told to prolong /a/ at a comfortable pitch and loudness level, three times in each position after being randomly allocated to two groups; Group A, who did this first standing then sitting, and Group B, who did this first sitting then standing. The researcher then timed the prolongations with a stopwatch and with the computer programme Praat. The longest time was then used for the participants' MPT and to measure the level of perturbation (jitter (local, %) and shimmer (local, dB)). Results: The results of this study showed no statistically significant positioning effect on MPT and shimmer (local, dB), however the results showed a small difference in the jitter (local, %) values for standing and sitting which approached the criterion for indicating a significant value. Conclusion: The study showed that there was no effect on the MPT of an individual and the level of shimmer (local, dB) that was obtained if the participants stood or sat. The results were a positive and encouraging clinical finding, as it indicates that either position may be used in clinic without affecting the results of a client's assessment and consequent decisions about diagnosis or management. However, the study did show that the level of jitter (local, %) measured may be affected by the positioning, but this needs to be confirmed by future research.