Vowel formant dispersion reflects severity of Apraxia of Speech
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1
University of South Carolina, Department of Communication Sciences and Disorders, United States
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2
University of South Carolina, Department of Communication Sciences and Disorders, United States
Introduction
Apraxia of Speech (AOS) is difficult to differentiate from aphasic production problems and from dysarthria. Diagnostically, it would be an improvement if AOS were more clearly characterized in objectively measurable phonetic-acoustic terms. Deviations in consonantal voice-onset-time (VOT) have been associated with AOS, though without clear specificity, and a common assumption is that vowel production is spared. However, if control over the speech apparatus is inconsistently impaired, this should be reflected in increased variance of vowel formant production, different formants reflecting different aspects of vocal-tract shape. Previous studies investigating vowel production have been inconclusive. We measured formants in vowels produced during spontaneous speech by speakers with and without AOS, and assessed to what extent their dispersion was predictive of AOS severity, based on the Apraxia of Speech Rating Scale (ASRS; Strand et al., 2014).
Method
Connected-speech samples were taken from 19 stroke survivors (7 female, mean age 59 (38-77); mean WAB-R AQ 76.5 (23.6-99.2)). 16 Participants had aphasia, 8 were clinically diagnosed with AOS (7 concommitant with aphasia, and 4 were diagnosed with dysarthria (3 concommitant with AOS). We identified the following American-English vowels bearing main stress in open-class words: /æ, ɜ, ɑ, ɛ, i, ɪ, ɔ, ɒ, u, ʊ, ʌ/, extracted the first three formants in PRAAT (Boersma, 2001), and calculated standard deviations around the means of these formants. Average VOTs for voiced and unvoiced consonants were also measured, and standard deviations around their means calculated. Correlations were assessed between these variables and aphasia severity (WAB-R AQ), AOS severity (ASRS) and the presence of dysarthria, for all vowels separately, to identify potential phonetic-acoustic predictors of AOS.
Results
Results vary per vowel, with formant dispersion of some vowels not correlating with AOS severity at all. However, AOS severity positively correlated (p<.05) with F1 dispersion in /æ/ (r=.470), with F2 dispersion in /ɑ/ (r=.647) and /u/ (r=.660), and with F3 dispersion in /u/ (r=.638). By contrast, VOT dispersion of voiced and voiceless consonants did not correlate with AOS severity (r=.336 and .266), nor did these measures generally correlate with formant dispersions, except for voiced VOT and the F3s of /ɜ/ (r=.646) and /ɔ/ (r=-.482; negative), and the F2 of /ɒ/ (r=.545). The latter was also predictive of dysarthria (r=.532), as was F3 dispersion of /u/ (r=.682).
Discussion and Conclusion
Given these preliminary results, it seems that the dispersion of F1 in /æ/ and F2 in /ɑ/ and /u/ are the best predictors of AOS severity among the variables tested, even in isolation. These phonetic-acoustic measures correlate with AOS severity, without correlating with aphasia severity or dysarthria, and can be obtained objectively, reducing the clinical subjectivity of AOS diagnosis. In addition, these results suggest that speakers with AOS do have problems with articulatory control over vowels. Further analyses will focus on optimizing the predictive quality of these measures by clustering formant and VOT dispersion values, with the ultimate goal of providing a maximally automatized analysis tool for spontaneous speech, to be used in aid of the differential diagnosis of AOS.
References
Boersma, Paul (2001). Praat, a system for doing phonetics by computer. Glot International, 5:9/10, 341-345.
Strand, E.A., Duffy, J.R., Clark, H.M. & Josephs, K (2014) The Apraxia of Speech Rating Scale: a tool for diagnosis and description of apraxia of speech. Journal of Communication Disorders, 51, 43-50.
Keywords:
apraxia of speech,
Vowel formants,
voice onset time,
Speech,
phonetic variance
Conference:
54th Annual Academy of Aphasia Meeting, Llandudno, United Kingdom, 16 Oct - 18 Oct, 2016.
Presentation Type:
Poster Sessions
Topic:
Academy of Aphasia
Citation:
Den Ouden
DB,
Galkina
E,
Basilakos
A and
Fridriksson
J
(2016). Vowel formant dispersion reflects severity of Apraxia of Speech.
Front. Psychol.
Conference Abstract:
54th Annual Academy of Aphasia Meeting.
doi: 10.3389/conf.fpsyg.2016.68.00130
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Received:
01 May 2016;
Published Online:
15 Aug 2016.
*
Correspondence:
PhD. Dirk B Den Ouden, University of South Carolina, Department of Communication Sciences and Disorders, Columbia, South Carolina, 29208, United States, denouden@chapman.edu