title: Assessing Vowel Centralization in Dysarthria: A Comparison of Methods.
abstract: The strength of the relationship between vowel centralization measures and perceptual ratings of dysarthria severity has varied considerably across reports. This article evaluates methods of acoustic-perceptual analysis to determine whether procedural changes can strengthen the association between these measures.
  
  
  
  Sixty-one speakers (17 healthy individuals and 44 speakers with dysarthria) read a standard passage. To obtain acoustic data, 2 points of formant extraction (midpoint and articulatory point) and 2 frequency measures (Hz and Bark) were trialed. Both vowel space area and an adapted formant centralization ratio were calculated using first and second formants of speakers' corner vowels. Twenty-eight listeners rated speech samples using different prompts: one with a focus on intelligibility, the other on speech precision.
  
  
  
  Perceptually, listener ratings of speech precision provided the best index of acoustic change. Acoustically, the combined use of an articulatory-based formant extraction point, Bark frequency units, and the formant centralization ratio was most effective in explaining perceptual ratings. This combination of procedures resulted in an increase of 17% to 27% explained variance between measures.
  
  
  
  The procedures researchers use to assess articulatory impairment can significantly alter the strength of relationship between acoustic and perceptual measures. Procedures that maximize this relationship are recommended.
authors.affiliation: Department of Communication Disorders and New Zealand Institute of Language, Brain & Behaviour, University of Canterbury, Christchurch.
authors.forename: Annalise R
authors.initials: AR
authors.lastname: Fletcher
authors.affiliation: Department of Communication Disorders and New Zealand Institute of Language, Brain & Behaviour, University of Canterbury, Christchurch.
authors.forename: Megan J
authors.initials: MJ
authors.lastname: McAuliffe
authors.affiliation: School of Communication Science & Disorders, Florida State University, Tallahassee.
authors.forename: Kaitlin L
authors.initials: KL
authors.lastname: Lansford
authors.affiliation: Department of Speech and Hearing Science, Arizona State University, Tempe.
authors.forename: Julie M
authors.initials: JM
authors.lastname: Liss
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D004401:Dysarthria / Q000175:diagnosis* / Q000503:physiopathology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010700:Phonetics; D011932:Reading; D015203:Reproducibility of Results; D013018:Sound Spectrography; D013061:Speech Acoustics; D013065:Speech Intelligibility; D013068:Speech Production Measurement / Q000379:methods*