A frequent acoustic sign of speech motor delay (SMD).
Lawrence D Shriberg, Yvonne E Wren
PMID 30945568WHAT IT FOUND
Children and adults with speech motor delay had longer mid-vowel and diphthong durations in continuous speech than speech-delayed controls without motor speech disorder.
This sign was frequent in USA and complex neurodevelopmental disorder groups.
Key findings
01Over 50% of participants with speech motor delay in the three groups were positive for increased duration of mid-vowels and diphthongs, and it was the only acoustic sign meeting that frequent-sign criterion.
02In continuous speech, participants with speech motor delay had significantly longer average mid-vowel and diphthong durations than participants with no motor speech disorder in both the USA and complex neurodevelopmental disorder groups.
03In continuous speech, participants with speech motor delay averaged 39.6% longer duration on /ɪ/, 21.8% on /ɛ/, 25.6% on /ɝ/, and 28.6% on /oʊ/ than participants with no motor speech disorder.
STILL TO COME
How it was doneWhat they foundWhat it means for SLPs
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What it does not show
This was an initial acoustic study, not a diagnostic accuracy study or a treatment study. The frequent-sign rule was an arbitrary criterion set at over 50% of speakers with speech motor delay having scores more than 1.25 standard units from typical speakers. The ALSPAC group had only 9 participants classified as having speech motor delay, and the authors state this is not a prevalence estimate. The complex neurodevelopmental disorder word-imitation comparison had only 11 participants in each group. Dialect and transcription constraints meant ALSPAC classification used only acoustic signs, not the full Precision-Stability Index. The USA word-imitation comparison did not show a significant difference, so the finding was not consistent across every task.
Declared interests
Funded by the National Institute of Child Health and Human Development, University of Bristol, Medical Research Council, National Institute on Deafness and Other Communication Disorders, and Wellcome Trust. The supplied text does not report author conflicts of interest.
The easy way to misread this
Do not use longer vowel duration as a confirmed diagnostic marker or treatment target. This was an initial study with an arbitrary frequent-sign threshold, an ALSPAC subgroup of only 9 participants, and no test of whether the finding changes clinical decisions.