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Vowel targeting in apraxia of speech: Preliminary findings of a bite block study
Adam Jacks, Thomas P. Marquardt, and Sarah Key-Delyria

Vowel targeting was examined in two adults with acquired apraxia of speech in a normal speaking condition and two bite block conditions (small and large). The vowels [?], [?], and [æ] were produced in isolation and in VC context. Acoustic analysis was performed to determine formant frequency values at the first glottal pulse and the vowel nucleus. Perceptual vowel goodness ratings for each token were obtained using direct magnitude estimation, and ideal formant “targets” determined for each vowel on the basis of actual formant measures weighted by vowel goodness ratings. Vowel targeting was assessed by calculating Euclidean distances in F1 x F2 space between each vowel token and the perceptually-weighted vowel formant target. Acoustic distinctiveness of adjacent vowels was assessed using an acoustic distance ratio, i.e. the distance between formant values of two vowels divided by the variance within the vowels. Differences between participants were noted and appear to be related to apraxia severity. Findings indicate greatest accuracy of vowel targeting in the normal speaking condition, followed by the small bite block condition, with poorest accuracy for the large block condition. Distinctiveness of adjacent vowel pairs followed a similar pattern.

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