![]() The rationale being that this provides a consistent measurement point that is as temporally removed from adjacent consonants as possible. In the motor speech literature, formant measurements are almost universally taken from vowels' temporal midpoints. To accomplish this, we will evaluate the following techniques known to vary across studies: (a) the time point at which formant extraction occurs, (b) the method by which vowel centralization is calculated, and (c) the cues provided to listeners in their perceptual measurement of speech disorder.Time Point of Formant Extraction Second, to make recommendations for future studies, we will determine which set of procedures produces the strongest relationship between the acoustic and perceptual measurements. First, we will determine whether, and to what degree, changes in procedures affect the relationship between vowel centralization measurements and perceptual ratings. This article will compare procedures used to measure both vowel centralization and listeners' perceptions of dysarthric speech. Across studies, there are considerable differences in research methods used, and the contribution of these methods to results has thus far been overlooked. ![]() However, we hypothesize that this is not the only cause. Kim, Hasegawa-Johnson, & Perlman, 2011) of the variance in perceptual ratings of dysarthric speech (for a more detailed review, see Lansford & Liss, 2014a).Īs Lansford and Liss (2014a) speculate, much of this inconsistency may be due to differences in the perceptual characteristics of participants' dysarthria from one study to another (e.g., there have been large differences in the severity of dysarthria exhibited by participants across studies). Indeed, VSA has been reported to account for both between 6% to 8% ( Tjaden & Wilding, 2004) and 69% ( H. Unfortunately, VSA measurements have high interspeaker variability and have traditionally demonstrated variable success in distinguishing healthy and disordered speech ( Sapir, Ramig, Spielman, & Fox, 2010). ![]() Static vowel formant values can be extracted across a range of word tokens, enabling measurements to be taken from a variety of speech stimuli. In the motor speech literature, the most common way of measuring vowel centralization is through the calculation of vowel space area (VSA)-using the first and second formants of a dialect's corner vowels. Understanding causes of variation in the relationship between acoustic and perceptual data is a first step toward establishing stronger links between these variables.Ĭentralization of vowel formants has been associated with reduced intelligibility in both healthy speakers and those with motor speech disorders (e.g., Ferguson & Kewley-Port, 2007 Liu, Tsao, & Kuhl, 2005 Neel, 2008 Tjaden & Wilding, 2004). Linking measurements of the speech signal to perceptual outcomes is an important component of validating acoustic metrics for clinical use. Although studies have consistently reported an association between acoustic vowel centralization and perceptual measures, the strength of these relationships is highly variable ( Lansford & Liss, 2014a). However, there are significant limitations in using acoustic metrics to infer information about listeners' perceptions of the disorder. Acoustic analysis of vowel sounds offers an objective assessment tool for measuring speech production in people with dysarthria. ![]()
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